Restoring & Modifying 1971 OIF TR120

[NM Bonny]

First question you should ask is, "define "very good"" - the conical hub is a drum brake made over fifty years ago; then, many of the vehicles around the bikes had the same* or similar drum brakes even on the front wheels of the vehicles; today, you will struggle to find any common vehicle with drums on the rear wheels, never mind on the fronts.

Second and third questions you should maybe ask yourself are, "Why have "longer levers" been available commercially for decades just for this BSA/Triumph front brake?" and "Why do I need "longer levers" on a "very good" brake?" ...

Then remember:-

. The conical hub was such a "very good" front brake, BSA/Triumph only fitted it for two model years, before swapping to front discs.

. Nevertheless, during just those two years, it earned epithets, "comical hub", "chronic hub", etc.

. Whoever at BSA/Triumph decided the same front brake would work on 250 singles and 750 triples weighing twice as much and producing three times the power was imho insane; e.g. contemporary Suzuki GT750 and GT550 were fitted with 4LS front drums ...

. Meriden started the 73 model year building around 500 650 twins; about two-thirds were fitted with the 'pre conical' 8" TLS drum in the conical forks, many at the specific request of the Australian Triumph importer that took the bikes.

. Emergency braking in the 21st century with a front disc brake, if you hit the object you were trying to avoid, you were going to hit the object braking with a conical hub. However, emergency braking in the 21st century with a front conical hub, if you hit the object you were trying to avoid, you do not get a re-run with a front disc to see if you would have missed the object ...

My long term experience of drum front brakes is limited to a T150 with the pre-conical. I do not use that bike for long-distance touring or two-up riding because the T160 with twin front discs simply has far better brakes. The T150's front pre-conical is ok when using the bike's performance away from busy traffic. However, a possible indication of how close the pre-conical is to its limit is, if I use the T150 for a classic track day, the front brake starts to fade about two-thirds of the way through a usually half hour session ... Afaik, no one has ever tried to say the conical front drum is better than the Triumph pre-conical TLS ...

*The BSA/Triumph conical hub brake is based on a design used earlier on British cars and small vans, there the design was praised for good (contemporary) performance and easy maintenance. However, they were made of steel and operated hydraulically. Otoh, BSA/Triumph decided to make their conical hubs in aluminium alloy and operate them with a cable that both pulled one shoe lever and pushed the other ... all good theoretical ideas individually but, having built them into one brake, afaict no one thought the brake should actually be tested in all intended fittings (e.g. 250 single and 750 triple) before committing to selling it to Joe Public ...

I'm sure you're right about all of this - which is why I was leaning toward just putting together my DIY 11.5" front disc conversion discussed earlier. But then I get influenced in by the 'but it looks so cool!' and 'shouldn't I give it a chance?' impulses and I find myself waffling.

Reality is, I did have (and still vividly remember) the fact-based, gray hair-producing experiences with the TLS front brake on my '71 Yamaha XS1B--the Japanese clone of the bike I now own--which resemble your above experiences. I was riding in the mountains just east of San Diego, and they were good for a few hard pulls, thereafter fading into fright-inducing mush. I should just make up the nifty conversion I've already got the slides, axle, and hub to complete. And, heck, it'll look very tidy as well as performing far better.

But, man, that aluminum air scoop...

 

[speedrattle]

Question: my tach, like yours, has no redline indicated. What is a safe figure for an internally stock Unit 650? And what about if I were to install a 750 kit later on? Any difference from the slight additional mass of the larger pistons?

assuming that your valve train has decent springs and your camshafts are reasonable, the two things to pay attention to with rpm are mean piston speed and ring flutter. around 3500 feet per second is said to be a more or less safe piston speed. approaching 4000 is pushing the envelope. the last time i calculated it, 3500 worked out to be around 6700, iirc? the calculated ring flutter rpm was also somewhere near that. peak torque for these things is around 6800, so above that level you can get more horsepower but with diminishing returns.

now im curious so ill go calculate the numbers again. i have a 1972 750 morgo that i run without rebalancing, and it will easily spin to 7000, but i keep it lower than that because im still running the original aluminum rods. when i next take it down ill replace them with steel.

if you build the motors to take it you can get much more than 7000, but realistically you ought to have a reason to be going there. my morgo goes 117mph with only 150psi cranking compression, and thats only around 6600? id have to look at my notes. thats fast enough for a street legal machine for me.

 

[NM Bonny]

assuming that your valve train has decent springs and your camshafts are reasonable, the two things to pay attention to with rpm are mean piston speed and ring flutter. around 3500 feet per second is said to be a more or less safe piston speed. approaching 4000 is pushing the envelope. the last time i calculated it, 3500 worked out to be around 6700, iirc? the calculated ring flutter rpm was also somewhere near that. peak torque for these things is around 6800, so above that level you can get more horsepower but with diminishing returns.

now im curious so ill go calculate the numbers again. i have a 1972 750 morgo that i run without rebalancing, and it will easily spin to 7000, but i keep it lower than that because im still running the original aluminum rods. when i next take it down ill replace them with steel.

if you build the motors to take it you can get much more than 7000, but realistically you ought to have a reason to be going there. my morgo goes 117mph with only 150psi cranking compression, and thats only around 6600? id have to look at my notes. thats fast enough for a street legal machine for me.

Thanks for this.

So, it's looking like for my purposes--that is, an extra layer of safety until I get around to rebuilding the engine (I've merely resealed the rocker cover, as the compression was good enough to ride around on for a while)--I'll just default to 6,500 rpms as an 'at-a-glance' redline. Perhaps at some point I'll add a redline to the gauge--but for now having a 'go/no-go' figure is helpful.

And, yes - over a ton is very fast on a motorcycle--any motorcycle. I have gotten off at ~60 mph on the Ocean Beach Freeway--the stretch of I-8 that extends west from I-25 to the ocean in San Diego--astride a 1938 Harley flathead with 8" over tubes, and that was way faster than I ever want to get off again. Ouch.

Interestingly, I saw in the specs in the workshop manual that my carbide cutters for the A-Series head might work for the valve seats in this bike. Very nice, as I prefer to do my own three-angle valve jobs and R&R my own guides. In my experience, many machine shops ream the guides too far down on the spec range, and in air-cooled engines that can lead to seized exhaust valves--as it did in the brand-new 'ready to run' S&S Shovelheads I fitted to my '51 FL. Luckily, no piston damage, so I just installed new Kibblewhites, recut the seats (lousy job with a too-thin sealing angle), adjusted the guide I.D., and have not had another issue since...

Thanks, too, for introducing me to Morgo, Inc. I was unaware of them and now am excited about converting my bike with their 750 kit, upgraded oil pump, etc., when the original engine wears out. Very cool! I enjoy the '51 FL but am increasingly thinking it'll get sold when this bike is set up the way I want it...

 

[speedrattle]

ive run the morgo for over 30 years. bolt-on kit. standard compression ratio is 9.5 to 1, i think, but you can go to 10.5. i have a four plug head, so i run 87 octane in it.

aerco makes another kit, which is apparently high quality as well.

the kits dont give you much more top end without head work, but theres more low and midrange. with porting and carb modifications they are a really sweet improvement.

theres a bit more vibration, but shoot, its a 360 crank.

btw, if you run very high rpm on a stock crank routinely, it will eventually fail. i dont know where the boundaries are, but you can exceed them.

 

[NM Bonny]

ive run the morgo for over 30 years. bolt-on kit. standard compression ratio is 9.5 to 1, i think, but you can go to 10.5. i have a four plug head, so i run 87 octane in it.

aerco makes another kit, which is apparently high quality as well.

the kits dont give you much more top end without head work, but theres more low and midrange. with porting and carb modifications they are a really sweet improvement.

theres a bit more vibration, but shoot, its a 360 crank.

btw, if you run very high rpm on a stock crank routinely, it will eventually fail. i dont know where the boundaries are, but you can exceed them.

Sounds like a really nice kit. I'll check out the Aerco version, too.

I'm eager to see how cruising at 70 mph feels astride the 650 Unit compared to the '51 FL, which I call The Paint Shaker (I like HWY 313 and 550, which are 55 and 70 mph limits, respectively). The FL is fine at 65~70 but the vibration of that 74 CID engine with its whacky single-pin crank is fairly pronounced as you near 70 per. She'll run all day in that range, mind you, but there's a reason the footboards have a half-dozen rubber pucks isolating the upper and lower steel panels...

I have a feeling, and I hope it's right, that the vibration I've heard people describe coming from the 40 CID 650 Unit is nothing compared to The Paint Shaker.

Wow... that's a lot of compression. The premium gas around here is 91 octane, if memory serves, so I don't think I'd want to go anywhere near 10.5:1.

 

[NM Bonny]

Kevin,

Did you go for Morgo's rotary or upgraded plunger-style oil pump when you increased to 750cc? They claim "an increase in performance over the standard oil pump" for the plunger-style, but that their "Super Rotary pump is capable of delivering approximately twice the oil of a standard plunger pump even when the oil is very hot."

It should, as it's twice as much. What's your experience if any with the rotary pump?

Joel

 

[NM Bonny]

I forgot to re-pose this question: "anyone know where on the engine a second breather is added?" I ask because I've seen mention of it in threads dedicated to hot-rodded Unit 650s and 750 conversions.

My only potential qualm would be whether adding one might reduce oil spray/mist from crank L/H end shown in shop manual's diagram of oiling system--and which would seem to be beneficial to primary chain. Is that an issue?

 

[NM Bonny]

Regarding the bolt-on finned aluminum manifolds like these to which I'd linked earlier (see pic), if I'm understanding the drawings of 'early' and 'later model' heads in the above catalogue, I can't fit such spacers because I've got the 'early' style screw-in manifolds.

So, if I want finned pieces, I'd have to turn my own from 6061-T6 aluminum round stock, with: (i) threaded holes to receive appropriate-length carb studs--rather than through holes; (ii) large threads cut into the O.D. of the piece to screw into my heads and receive the OEM thin locking nuts; and (iii) threaded holes in an appropriate location to receive the OEM (or aftermarket aluminum) nipples for the crossover tube.

I might make some of those up if vapor lock becomes an issue. If I do, and if anyone watching this thread would be interested in a pair of such manifolds, please let me know, as the cost of making up a one-off pair is virtually the same as making a short run of parts vis-a-vis time on the big CNC lathe and mill. I can likely get a remnant of the aluminum stock for a one-off pair, but it isn't extraordinarily expensive to buy a 6' length of round 6061-T6, so the material cost per part would be the minority portion of the cost.

If I were to make up such a part, is there an existing Trump stud part no. that would work to affix Amal 900 Series concentric carbs and leave room for the OEM thick O-rings and mounting cups, small rubber O-rings, and nuts?

 

[Rudie]

Regarding the bolt-on finned aluminum manifolds like these to which I'd linked earlier (see pic), if I'm understanding the drawings of 'early' and 'later model' heads in the above catalogue, I can't fit such spacers because I've got the 'early' style screw-in manifolds.

Correct.

existing Trump stud part no. that would work to affix Amal 900 Series concentric carbs and leave room for the OEM thick O-rings and mounting cups, small rubber O-rings, and nuts?

Tap a good long time Triumph parts dealer? The 69-72 studs probably are available separately from the manifold now, you need a current dealer's knowledge of the part number.

That said, you will be at the mercy of current Far Eastern accuracy. Access to a lathe, I would be inclined to turn them myself, I would be able to spend time tweaking the 'step' position accurately, I would probably add a little extra length to the 1/4" o.d. part to ensure a thread or two was definitely visible after the self locking nuts were tight.

 

[NM Bonny]

Correct.


Tap a good long time Triumph parts dealer? The 69-72 studs probably are available separately from the manifold now, you need a current dealer's knowledge of the part number.

That said, you will be at the mercy of current Far Eastern accuracy. Access to a lathe, I would be inclined to turn them myself, I would be able to spend time tweaking the 'step' position accurately, I would probably add a little extra length to the 1/4" o.d. part to ensure a thread or two was definitely visible after the self locking nuts were tight.

On the studs:

Sounds good, thanks. I mean, I can always try McMaster Carr et al. if there aren't good options from Brit motorcycle vendors. It's just nice to be able to take advantage of the economy of scale savings from existing manufacturers if possible.

On the bespoke manifolds:

I don't avail myself of overseas machining. All my parts are made here in NM by one of two family-owned shops, or by me working in the smaller one down the block from my place, where I'm an informal apprentice.

You're absolutely right that it's vital during R&D to be able to try a part out on the vehicle before investing in a production run--and quality control is a cinch right next door. Check out the difference between (for instance) the runout on my A-Series serpentine belt crank pulley and the one that Moss Motors has made overseas, in the videos linked from this page. The little blip in the needle on mine is lint or a cookie crumb from the foreman's fingers...

Agreed on the number of threads to play it safe--good idea.

Due to the nature of attachment of the old-style manifolds, which requires rotation of the part to screw into the head, the length of the fins would be quite limited--at least for the green portion indicated in this photo.

Now, I could have longer fins for the orange portion--and of course the manifolds could be longer overall, thus making room for a few more fins. I'll have to take measurements but at least with my style of side covers, I believe there's room for a big more length--so long as one uses the K&N filters I opted for. And the aluminum would dissipate heat far better than the steel pipes do, even if there were no fins at all...

Huh... Might be a fun project--after I get the front brake sort, that is!

BTW - My new Trademark, Red River Hogs, finally got approved by the PTO (it's a circuitous DIY application process but not too terrible: most people don't know that the PTO staff attorneys do the search for you, so you don't have to pay a lawyer to do that up front). So, if I decided to make this sort of motorcycle-related part, it would be vended under that moniker, rather than the A-Series-related stuff under Creative Spridgets.

 

[Rudie]

On the studs:

I can always try McMaster Carr et al.

Mmmm ... even if stepped 5/16"-1/4" studs are available, the length of the 5/16" o.d. part between the manifold and the step has to be very accurate, so the E9711 and E9554 rings are compressed a little by the nuts and E9555 washers to isolate carbs from vibration, but the rings are not so compressed they cannot isolate the carbs.

I don't avail myself of overseas machining. All my parts are made here in NM

you will be at the mercy of current Far Eastern accuracy

... was referring to buying studs from a Triumph parts dealer.

Due to the nature of attachment of the old-style manifolds, which requires rotation of the part to screw into the head, the length of the fins would be quite limited

the manifolds could be longer overall

You know inlet tract length affects cylinder filling differently at different rpm? Changing inlet tract length could improve cylinder filling at the rpm you will want to use most, but could also affect cylinder filling adversely at that same rpm?

My new Trademark, Red River Hogs, finally got approved by the PTO

 

[NM Bonny]

Mmmm ... even if stepped 5/16"-1/4" studs are available, the length of the 5/16" o.d. part between the manifold and the step has to be very accurate, so the E9711 and E9554 rings are compressed a little by the nuts and E9555 washers to isolate carbs from vibration, but the rings are not so compressed they cannot isolate the carbs.


To be clear, "you will be at the mercy of current Far Eastern accuracy" in my previous post was referring to buying studs from a Triumph parts dealer.


You know inlet tract length affects cylinder filling differently at different rpm? Changing inlet tract length could improve cylinder filling at the rpm you will want to use most, but could also affect cylinder filling adversely at that same rpm?

Understood on the length and design of the studs - thank you. Indeed, it may turn out that with the simple addition of the thick O-rings, I don't experience any significant vapor lock. Honestly, even when that phenomenon rears its head with the '51 FL, I just hold the throttle open, kick her a few times (wary of a nasty, ankle-spraining kick-back), and off I go. With a 40 CID engine as compared to the FL's 74 CID, we're ultimately talking a matter of convenience. I've never been stranded--and that's running a carb with an accelerator pump. I wouldn't think flooding/vapor lock is quite as much of an issue with the Amals--or am I wrong about that?

The vapor lock issue aside, on the intake tract length, yes I'm aware of that factor affecting flow dynamics inside the combustion chamber. However, in my experience tuning carbureted, side-draft engines, a difference of 1/2~1" on a straight manifold runner should have a relatively small effect, if it's measurable at all on a street bike without a dyno and deep pockets (I'm retired and not wealthy).

In general, a longer tract tends to increase torque in the low to mid range--but we're talking significantly longer. Also, there are so many factors involved, like whether you're initiating, maintaining, eliminating, or increasing/decreasing a vortex or turbulence (which can be functional or dysfunctional), that one either does a lot of math and flow-testing or just makes up a part and tries it out.

I gave the flow bench I made years ago in CA to a community college auto shop, so am limited to the latter approach, informed by some educated guesses (which worked very well with the HIF44 ram pipe/snorkel adapter I designed, in both standard and 'tunable' blow-through versions - re: the latter, check out Doug's car in the second video, which has a forced-induction cam and really scoots).

But luckily, the outer limits of the part I had in mind are defined by the side covers and air cleaner clearance, so I don't think we'd get long enough to make a big difference. I could j-u-s-t fit taller K&Ns like Kevin's now, but if I make up a slightly extended manifold in order to add a few fins, may be limited to the shorty filters I now use.

And, then, most people buy side covers rather than bending up their own as I did. So, ultimately I could end up making one pair of something only I would use. And that's okay, too, as I'm just looking to have some fun.

 

[speedrattle]

Kevin,

Did you go for Morgo's rotary or upgraded plunger-style oil pump when you increased to 750cc? They claim "an increase in performance over the standard oil pump" for the plunger-style, but that their "Super Rotary pump is capable of delivering approximately twice the oil of a standard plunger pump even when the oil is very hot."

It should, as it's twice as much. What's your experience if any with the rotary pump?

Joel

the stock oil pump is quite good enough, if its in good condition and ykure not trying to pump sludge. ive had the same stock 1972 pump.in the morgo engine for the 46 years ive had it, and it still spurts and squirts just fine. i take it apart every now and then to check for scoring and wear, but the pistons snap back every time. i use a morgo pump in a race bike just for the nominal extra pumping capacity, and because they are made so well. but i think a stock pump would have worked there too. the pump i took out had been destroyed by someone starting the machine without the aluminum slider block. they dont last very long when you do that.

i dont know much about the rotary pump, except that it must be primed before you run it. the stock piston pumps are self priming, and failing anything else i always look for fewer things to go wrong. maybe someone else here can offer some information about them.

triumph switched to a better oval port pump in 1970, i am told, which would be E9421 (70-9421). thats the one im familiar with. later on you can get the oval port pump with four check balls, which is supposed to be the best of the bunch. that number is 71-7317, i think.

whatever you do, take it apart and check for grit before you install it, and make sure the plungers (if you use one of those) snap back sharply when you pull against a finger closing the piston port. the pump should have zero detectable leakage around the pistons. also trim the pump gasket to make sure none of it is blocking any of the ports.

 

[NM Bonny]

the stock oil pump is quite good enough, if its in good condition. ive had a stock 1972 pump.in the morgo engine for over fifty years, and it still spurts and sputters just fine. i take it apart every now and then to check for scoring, but the pistons snap back every time. i use a morgo pump in a race bike just for the nominal extra pumping capacity, but i think a stock pump would have worked as well. the one i took out had been destroyed by someone starting the machine without the aluminum slider block.

i dont know much about the rotary pump, except that it must be primed before you run it. the stock piston pumps are self priming, and failing anything else i look for fewer things to go wrong. maybe someone else here can offer some information about them.

triumph switched to a better oval port pump in 1970, i am told, which would be E9421 (70-9421). thats the one im familiar with. later on you can get the oval port pump with four check balls, which is supposed to be the best of the bunch. that number is 71-7317, i think.

whatever you do, take it apart and check for grit before you install it, and make sure the plungers (if you use one of those) snap back sharply when you pull against a finger closing the piston port. the pump should have zero detectable leakage around the pistons. also trim the pump gasket to make sure none of it is blocking any of the ports.

Okay - thanks for this extensive info.

When I got the bike and ordered the initial round of parts in anticipation of pulling, polishing, and resealing the primary, timing, and kicker covers, I had bought new springs and balls--pretty much all they give you in a 'rebuild kit' aside from gaskets--and had read in the shop manual to inspect the aluminum sliding drive block for wear.

But this is great. If they're that robust and efficient, not much need to upgrade.

However, whenever this engine wears out--and I do the 750cc kit--I will install a 71-7317, which indeed checks out to be the four-valve model. I see you can get them for $150 on eBay or $80 Pounds BS here, though with shipping it's just $9.00 less than the eBay option with free shipping. The UK website says about the pump:

"Can also replace the standard dual plunger oil pump on earlier 6T, T120, TR6, TR7 and T140 models. You will need to replace the timing cover for the later type with the cutaway - 71-7318 or modify your existing cover to allow room for the allen screw heads. Note - modification will require grinding out the casting and possibly some welding." [emphasis added]

The cutaway to accommodate the Allen screws on the bottom of the pump to which they refer is presumably the little area marked in the attached photo, and which doesn't look hard to make with a die grinder. I don't think you'd need to do any welding, so not sure what that's about...

All of that said, I wonder whether the similarly priced Morgo 'upgraded' plunger pump delivers as well as the four-valve version. It seems like all that Morgo claims is closer tolerances...?

 

[speedrattle]

I forgot to re-pose this question: "anyone know where on the engine a second breather is added?" I ask because I've seen mention of it in threads dedicated to hot-rodded Unit 650s and 750 conversions.

My only potential qualm would be whether adding one might reduce oil spray/mist from crank L/H end shown in shop manual's diagram of oiling system--and which would seem to be beneficial to primary chain. Is that an issue?

you can add a breather to the timing chest cover, or to the triangular cavity holding the front motor mount bolt. drill a hole, install a hose barb, and route to the rear or a catch bottle.

people who install one in the crankcase timing plunger hole never seem pleased with it, because oil spray fills it too easily.

i use the front triangle cavity when i do it.

 

[speedrattle]

people say that the oval port pump squirts more volum, and so has higher pressure when warm. the one my race bike works fine to 8500 rpm

dont buy a cheap ebay pump. look for a dedicated supplier.

 

[NM Bonny]

people say that the oval port pump squirts more volum, and so has higher pressure when warm. the one my race bike works fine to 8500 rpm

dont buy a cheap ebay pump. look for a dedicated supplier.

Sounds like the one to get.

Absolutely - the pump I was looking at on eBay is an L.F. Harris International, genuine Triumph part. Sold by South Carolina British Cycles, who has been around a while. Looks like the same pump others sell for far more money.

 

[speedrattle]

harris pumps have a good reputation.

on tne primary oil theres only about 1/2 inch in tbe primary anyway, and it goes up and down a bit with rpm. most people install an extra breather because tbey put in a dry belt drive in a 1970 or newer motor and have to install a DS crankcase seal because the primary breather is no longer connected to tbe crankcase. tbe older camshift timed breatber is pretty small, imo.

you can install breather lines in both rocker inspection covers. the holes in the tappet blocks arent big, but the air pulses in rocker box breathers are quite noticeable.

 

[NM Bonny]

harris pumps have a good reputation.

on tne primary oil theres only about 1/2 inch in tbe primary anyway, and it goes up and down a bit with rpm. most people install an extra breather because tbey put in a dry belt drive in a 1970 or newer motor and have to install a DS crankcase seal because the primary breather is no longer connected to tbe crankcase. tbe older camshift timed breatber is pretty small, imo.

you can install breather lines in both rocker inspection covers. the holes in the tappet blocks arent big, but the air pulses in rocker box breathers are quite noticeable.

On the pump, glad that's your impression. I've ordered the LF Harris 71-7317 four-valve pump, which will go in a box labeled '750 conversion' for when the original engine wears out.

I have no immediate plan to switch to a dry primary on this bike. I run one on the '51 FL but mainly because it came with one fitted and those bikes weep like crazy in stock wet-primary trim.

Good info on the breather options, thanks. I'm eager to see how the existing breather--which I re-routed in 1/2" aluminum as per an earlier post--handles things. Should be fine, but if it struggles, now I've got a plan for a less obtrusive-looking, supplemental system.

Now, if only it would warm up a bit out in the garage. Sideways blowing snow today...

 

[NM Bonny]

The LF Harris pump shipped. I found this article discussing wet-dumping and the various pump options we've been talking about. Not very technical but reaches the same conclusion: a late-model 4-valve pump by a good manufacture like LF Harris is a solid option.

It also mentions that in their case, retro-fitting to an OIF early 650 like mine, they had to remove only the smallest amount of material from inside the timing cover to fit the pump. So, I'm confident that whenever I fit it--either in conjunction with the 750 upgrade or right away, if I find the existing, OEM pump to be garbage--that it'll be straightforward.