Multiple Bent Pushrods

[Woollybandit]

Head is off and apart from being full of carbon from running too rich (that job was on the end of the disastrous run.
No bent valves, marks or other issues so far.
Carbon cleaned off crowns an no marked in valve pockets.
I don't remember the studs staying in the cases in other bikes. Head JUST clears top tube to come off.
Valves coming out next to check guide fit. Then timing cover.

Wish me luck, I'm going in!

 

[Woollybandit]

All valves out and free sliding except up by collets but that’s 1-1/2” travel so not bothered by that.
Checked timing side and not being prepared to rotate engine up to 90+ times just slid out centre idler and reset cogs. Easy as rockers are on bench.
Waiting for pushrods and rocker box gaskets ….. old ones are torn at the pushrod holes and even the wire reinforced type are cheap enough. Makes it so much easier to locate rocker balls into rods with intact gaskets.
I didn’t do the clay test but you can see through the plug hole plenty of valve clearance.
All in all I can find no cause for the failures, oil present everywhere you’d expect, valve timing good, no piston impact, valves are totally true when rolled on flat plate. Engine never run above 5k but completed 50 miles since PO rebuild. Carburettor was obviously very rich but better than too lean, have cleaned and rebuilt Amal premier & will adjust needles upon restart.
It’s a mystery

 

[Bloodknot]

An interesting conundrum but I would suggest nothing whatsoever to do with the cams or the piston to valve clearance. The problem has to lie somewhere between the cam lobe and the tip of the valve stem as that part of the mechanism is the only portion that has any facility for adjustment.

This is assuming that the PO used the correct push rods (hopefully the existing ones), the valves were timed correctly using the dots on the cam wheels, the valve clearances were set correctly. So what could cause the valve clearances to not only disappear but to go negative giving rise to the curly push rods?

A quick question for @Woollybandit did you check the valve clearances before you started stripping the engine?

Remember that we have three bent rods so whatever it is, it’s happening on both cylinders. I would not be surprised if the fourth push rod was not truly straight.

1. Valves incapable of being fully depressed. “Valves are seated and bounce if stems hit with rubber hammer. Springs are seated in caps and no sign of piston impact.” If the cause was FOD it is highly unlikely to have happened to more than one valve.

2. Valves prevented from fully opening. “no sign of piston impact.” The workshop manual doesn’t express valve timing in degrees of crank rotation but I have found the information below in this Triumph publication.

Inlet valve open to closed is 60°+180°+80°=320°. Valve fully open after 160° of crank rotation which is 100° ATC, piston is over halfway down the bore.

Exhaust valve open to closed is 75°+180°+55°=310°. Valve fully open after 155° of crank rotation which is 80° ABC, piston is not yet halfway up the bore.

So the piston is in the lower half of the bore when either valve is fully open. Therefore piston/valve clash is highly unlikely.

3. Valves have clashed due to incorrect valve timing. The timing marks on the cam wheels will evidence this but you may have to rotate the crank up to 94 times as the gear teeth are set in a hunting configuration (every tooth on one wheel will eventually mesh with every slot on its companion wheel).

With the head off and a degree disc on the crankshaft and using the one straightish push rod this should be easy to check. Note if checking this using valve movement you should be aware that both rocker arms have a ratio of 1.1 I.e. 110% of cam lift.

4. You might check the order of the components on the rocker shafts as I understand that for some machines this can be an issue.

5. The only other possibility I can think of is that on rebuilding the engine the PO forgot to set the valve clearances, or if he did the locknuts were not tightened. Thus allowing the pushrods to jump off of the tappets or fall away from the rocker arms allowing the crown of the tappet or rocker arm to sit on the rim of the pushrod end cap.

Whatever it was, was significant to have effectively reduced the length of the pushrod by that amount. Perhaps comparing the length of the one straightish pushrod with the bent ones may give a clear indication when compared to the depth of the socket in the end of the pushrod.

Incorrect valve timing or slack valve clearances would certainly have been reflected in the poor performance that was experienced.

 

[Woollybandit]

Hi Bloodknot

A quick question for @Woollybandit did you check the valve clearances before you started stripping the engine?

I too am now doubtful of valve impact. After visually watching through the plug hole the inlet valve disappear way before the piston rose to TDC was thinking that only if valves were sticking would they clash.
After removing each valve in turn and finding there was plenty of freedom in the guides at the operating positions there is no way they could be sticking, and no witness marks on stems to indicate that either. All valve heads slap back onto their seats perfectly. Head is back on and torqued down. Waiting for new pushrods now.


1. Valves incapable of being fully depressed.

The process of compressing springs and removing collets/valves shows they are capable of being depressed.


2……

Bloodknot, I really appreciate your work researching and writing out your above contribution and it’s printed off for the workshop files.
Thank you


3. Valves have clashed due to incorrect valve timing.

I started hand-winding the engine forward using the kickstart watching the pinions rotate but quickly realised that I wasn’t going to do that for 90+ revolutions. Having seen the clean valves and piston crowns I just pulled the intermediate pinion wheel and aligned the cams/crank wheels.


4. You might check the order of the components on the rocker shafts as I understand that for some machines this can be an issue.

I read that a couple of years ago on a bulletin, something to do with order of the Thackeray and plain thrust washers for good oiling in the rocker area. There was oil aplenty on the rockers when I dismantled boxes but I’ll check again tomorrow.


5. The only other possibility I can think of is that on rebuilding the engine the PO forgot to set the valve clearances, or if he did the locknuts were not tightened.

This is my favoured answer too.

EUREKA !! Just been out to the workshop (11pm!) and looked inside the rocker boxes and there are two great big gouges in the case. The rods have jumped/slipped off the rocker balls and stuck on the box body. Now I know what happened I need to think about why, because everything else in the train from the crank pinion to the valve heads looked normal. This might form an argument for NOT using gaskets with pushrod holes as without the holes the rods could slip sideways into open space instead of up against the rocker box to catch on.

 

[Woollybandit]

Just as a final thought (as I was lying in bed), I now suspect the rods were never on the rocker balls but were trapped between the ball shoulder and the box body where the dents are.
That would explain the lack of power, poor running and the way the gouges seem to have alloy shavings if you look closely. I think the rods moved up and down with their cup edge on the rocker body alongside the ball and pinched against the casing which is gradually shaved away until it finally dug in and bent itself.

 

[Rudie]

4. You might check the order of the components on the rocker shafts as I understand that for some machines this can be an issue.

I read that a couple of years ago on a bulletin, something to do with order of the Thackeray and plain thrust washers for good oiling in the rocker area.

The order of Thackeray and plain (Thrust) washers on rocker shafts:-

. illustrated in the 73-78 750 twin workshop manual is wrong;

. illustrated in the 73 750 twin parts book is correct ... Each rocker should have one 70-1575 1/2" i.d. Thrust washer each side of it, the spring Thackeray washer should be fitted between a Thrust washer and the side of the rocker box. However, consequently, the single 70-1330 3/8" i.d. Thrust washer shown on each rocker spindle is a misprint.

The change in the order of Thrust washers and Thackeray washers was made during 68 when Triumph stopped drilling an internal oilway in rockers to move oil from the rocker spindle to lubricate the pushrod ball.

There was oil aplenty on the rockers when I dismantled boxes

There will be as oil (deliberately) leaks out the sides of the rockers. However, the point of changing the order of Thackeray and (plain) thrust washers - so thrust washers were directly against both sides of any rocker - was so the oil (deliberately) leaking out the sides of the rockers was directed at the pushrod end of the rockers.

I’ll check again

If you find the 3/8" i.d. Thrust washer has been fitted at the inlet end of each rocker spindle, it will have been fitted between the Thackeray washer and the side of the rockerbox.

EUREKA !!
two great big gouges in the case. The rods have jumped/slipped off the rocker balls

More likely they were never fitted correctly when the rockerboxes were fitted; unless at some time you have backed off the adjusters completely and then turned over or started the engine?

When fitting pushrods on tappets and when fitting rockerboxes:-

. I put a blob of grease in each pushrod or tappet cup (the grease helps to keep tappet, pushrod and rocker stuck together during assembly and turning the engine to set the tappet clearances);

. before fitting, I position the engine so both either inlet or exhaust pushrod ends are at about the same height; when fitting, I hold the adjuster ends of the rockers up with fingers, so the pushrod ends of the rockers are as low as possible, contact the pushrod ends before the rockerbox contacts the head;

. first rockerbox fitted, I secure it to the head, turn the adjusters so all are in contact with the valve tips, then turn the engine to get the second pushrods about the same height for fitting the second rockerbox.

This might form an argument for NOT using gaskets with pushrod holes as without the holes the rods could slip sideways into open space instead of up against the rocker box to catch on.

As more (most?) likely the tappets, pushrods and rockers were not assembled correctly, gaskets without pushrod holes would only make a difference if ones with holes misaligned the pushrods for assembly.

I have never used rockerbox gaskets with pushrod holes, never bent a pushrod.

 

[brooke]

As usual, great to see we have so many knowledgeable helpers on TT . It’s been fifty years since I saw a Triumph push rod . I think GM V8’s still use push rods and make lots of power . With the trend toward turbos they could make a come back .The Honda CX 500 was of course pushed and turbocharged for 82 hp in 1982 ..

 

[Woollybandit]

… and yes, upon inspection the Thackeray washer/spring is in the wrong place next to the rocker (with coil end stuck in the slot!).
Rocker shaft seals on order with the gaskets and rods. Three long days to wait!

 

[Woollybandit]

The PO had the manual but not the Bulletins, although he did a great job on the bike. It’s the blue one in my profile picture

 

[Woollybandit]

Cracking job, if a little loud.

 

[grandpaul]

EUREKA !! Just been out to the workshop (11pm!) and looked inside the rocker boxes and there are two great big gouges in the case. The rods have jumped/slipped off the rocker balls and stuck on the box body. Now I know what happened I need to think about why, because everything else in the train from the crank pinion to the valve heads looked normal. This might form an argument for NOT using gaskets with pushrod holes as without the holes the rods could slip sideways into open space instead of up against the rocker box to catch on.

No, the pushrods will only ever slip off in that direction, ESPECIALLY without holes in the gaskets. That is why the rocker covers are always ONLY gouged behind, to the rear.

It's a TOUGH/DELICATE job to set those rocker tips down into the right spot. You can always use painter's tape to hold them from the adjuster end, lower them in place, then pull out the tape.

Glad it's figured out, happens all the time.

 

[Woollybandit]

Thanks. I use grease in the cups when I do it. Those rockers stick down on the rod cups like glue .... you know you've hit bullseye!

 

[Woollybandit]

Oh boy what an afternoon! Just spend a hour switching the washers around on the rocker shafts, bolted them down onto the head and then onto the tappet gaps.
After very carefully checking pushrod engagement and setting the gaps with feeler gauge pack as I finished the last one the feeler gauge pack fell apart in my hand!
I spent a half hour scouring the workshop floor with torch, brushed it and checked top of head fins looking for this M4 nut that went walkies. Checking in the rocker access opening I just saw the very edge of the nut trapped between the valve spring cap and the bottom of the rocker box. Thank god it was not a stainless nut as I managed to magnetise a thin screwdriver and extricate it.

I couldn’t NOT find that nut and I had visions of me taking the head etc all off again to put my mind at ease.

Time for a

 

[brooke]

Oh boy what an afternoon! Just spend a hour switching the washers around on the rocker shafts, bolted them down onto the head and then onto the tappet gaps.
After very carefully checking pushrod engagement and setting the gaps with feeler gauge pack as I finished the last one the feeler gauge pack fell apart in my hand!
I spent a half hour scouring the workshop floor with torch, brushed it and checked top of head fins looking for this M4 nut that went walkies. Checking in the rocker access opening I just saw the very edge of the nut trapped between the valve spring cap and the bottom of the rocker box. Thank god it was not a stainless nut as I managed to magnetise a thin screwdriver and extricate it.

I couldn’t NOT find that nut and I had visions of me taking the head etc all off again to put my mind at ease.

Time for a

Yep definitely time for . That kind of event happens here on a regular basis

 

[Woollybandit]

While this thread is fresh I noticed that the rocker shaft plain washer next to the Thackery washer on oil supply banjo side (bit of a mouthful!) is 3/8” and won’t slide over the shaft shoulder where it increases to nearly 1/2”. The other three are 1/2” diameter.
This means the offside rocker has a couple of mm of side float and the Thackery is compressed between box and plain washer. In the old order the Thackery having the larger I.D. would push the rocker towards the centreline.
Does that make sense?

Bottom line …… order a new set of 1/2” washers. It’s not just a case of re-ordering the components.

 

[grandpaul]

Dude... You need popsicle sticks. They're all the rage...

https://www.summitracing.com/parts/...QNqxgrMTDFsdk4GhmEwilUEUpl-Tk8xBoCxREQAvD_BwE
What doth hinder you?

 

[Woollybandit]

That’s a pro piece of gear.
I have a gauge set that’s an inch thick but only use 3 or 4 of them. I’ll get a ball chain and put those regularly used ones on it leaving the rest for those ‘special occasions’!

 

[grandpaul]

That’s a pro piece of gear.
I have a gauge set that’s an inch thick but only use 3 or 4 of them. I’ll get a ball chain and put those regularly used ones on it leaving the rest for those ‘special occasions’!

I bought a 3-piece set about 20 years ago, still have 'em!

 

[speedrattle]

i gave up on feeler gauges in old-style rocker boxes years ago and now just click and listen for 002 and 004. 008 and 010 i use the rotation of the 26 tpi adusters to measure clearance. dont have any 006 but id rotate those for clearance as well.

dial indicators work but theres little room

 

[Bloodknot]

I bought a 3-piece set about 20 years ago, still have 'em!

Mine were purchased in the 60s. The strange thing is having worked in the UK’s construction industry which went metric the very late 60s and also owning a Ducati for the last 20+ years you’d think that decimal portions of a millimetre would be second nature, but not so, I still think in thousandths of an inch.