68 T120R Bonnie bottom end overhaul

[grandpaul]

I've been contracted to overhaul the bottom end of a 68 T120R Bonnie, so here is the project posting.

Engine as it arrived; the case bolts were all loosened, client had started to disassemble it and decided to send it in instead-

Gear cluster & cam pinions had already been removed and were in a seperate box-

Timed breather disc spring was walkabout-

I never like to see excess silicone sealer squeezed inside engine oil cavities, this engine had plenty of that-

 

[grandpaul]

At some point in time, the crank's main oilway got mostly plugged-

The engine was more or less cleaned, but still had some trash in it here and there-

A loose primary chain started eating into the oil collector, then broke most of it off; not a big deal, there's enough oil sling to still do the job-

Dang those loose primary chains!

I'm betting that what's left of the alternator stator mounting studs are sawed through to the point they need to be replaced...

 

[grandpaul]

Stray silicone debris in the crank area, looking for trouble-

Crankcase sediment, not too bad, but I HATE the excess use of silicone-

Timed breather disc still happily in place-

More silicone trash in the tach drive cavity at the exhaust cam bushing, not good!

 

[grandpaul]

Main oil seal was "folded" and must have been leaking quite a bit...

More damage from the loose primary chain, near the adjuster opening; not a technical issue-

Grunt in the tach drive-

 

[grandpaul]

Drive sprocket knackered - "fishooked"-

Timing side exhaust cam bush was a loose fit in the case and had already started to spin. New bush will have to be oversized. Note the telltale spin scratch marks. Once it started to misalign, it also lost lubrication due to the lube hole no longer being aligned with it's supply (also note stray bits of silicone)-

El Grunt-o, but not nearly as bad as some I've seen!

Virtually new sump plug, with head already knackered-

 

[grandpaul]

Finally down to the crank; the rods turned freely on the journals without any "flop"-

The primary nose of the crank is well and truly knackered, that's going to need some rehab-

Sludge trap was never opened since being peened shut at the factory-

Sludge accumulation at the mouth was about 30%, but increased to 50% at the bottom-

 

[grandpaul]

This is the worst of it. Sludge accumulation had blocked off the rod journal oiling holes on the left journal, and the damage started. Thankfully, it wasn't too bad. I still can't figure out the wierd scratchings on the accummulation-

Right side oil holes were fine-

Pretty obvious difference, even with a blurry photo (sorry)-

"The remains of the day"; I couldn't get the bugger out without destroying it (my acetylene tank is empty, else I'm sure heat would have helped) I should have scraped out the tube, but you get the idea...

 

[grandpaul]

Strange, but the left side shells look better than the right side! Still, they're already well into the sacrificial material-

The rods were in decent shape, a couple of very minor nicks here and there; obvious signs of overheating due to improper lubrication (thanks to the blocked journal oil holes)-

That's it for the tear-down. Now to put together the parts list and get the order in...

 

[grandpaul]

Sludge tube was COMPLETELY full at the bottom end-

Cut it open and scraped out most of the crud-

.5 oz according to the USPS scale (definitely enough to affect the crank's balance)-

A good long solvent wash will help, then a bottle brush "just in case", followed by a wire probe, then another long wash-

 

[grandpaul]

This is a triple-post from my forum & TriumphRat (client's "home" forum), so a bit of a hassle. Still, I thought some of y'all might be interested, so I'm going to go start to finish here as well.

 

[Rocky]

Thanks for posting the pics. I've been there and done that with my own Triumph, but my engine was in much better shape and not as abused.
I groaned with dismay when I saw the abuse this poor old engine has been put through.
You have your work cut out for you. Let us know how things go.

 

[CarlS]

I can relate to that sludge trap... But I learned! :y114:

 

[munkybarz]

[quote author=Rocky link=topic=9280.msg45620#msg45620 date=1268910078]
......I groaned with dismay when I saw the abuse this poor old engine has been put through.
You have your work cut out for you. Let us know how things go......
[/quote]
Are you sitting down? Hope so, look at this;

 

[CarlS]

Wow! Has it been under water?

 

[The Seeker]

[quote author=munkybarz link=topic=9280.msg45798#msg45798 date=1269807334]
Are you sitting down? Hope so, look at this;

[/quote]

OH MY GOD!!!

 

[grandpaul]

[quote author=munkybarz link=topic=9280.msg45798#msg45798 date=1269807334]
Are you sitting down? Hope so, look at this; < photo of rusty crank >[/quote]

Welcome to the forum, munkybarz.

The amazing thing is, since both cranks still need to be thoroughly cleaned, polished and have new bearing shells installed, the rusty crank is in MUCH better shape! All the splines and the rotor keyway are in perfect condition, and the rotor stud threads look to be okay with a simple thread chase. As long as the opposite end nose isn't "mushroomed" from hammering the crank out of the block (probably not, as it's still in the right side case half), it's a very nice donor crank for rebuild.

 

[CarlS]

Paul, was the engine open and the sitting outside or was the bike flooded? That is the rustiest crank I have ever seen in anything.

 

[munkybarz]

Bill here,
This is the 1969 T120R that was in the 1967 bobber/chopper that I scooped back in January. It has sat since 1980. Out in the rain, I dunno, in a canal, sheesh, who knows. Anyway, the top end was so seized that I had to make a 5/8&quot; plate jig up to drive the pistons down just so I could get the cylinders of of the cases.

What you see is the cylinders after removal. I patterned the holes in the plate exactly using transfer punches and then on centre of each cylinder I used some 1/2&quot; 20 threaded rod with jam nuts on top and used my electric impact wrench to drive the pistons down to BDC. The 3/8&quot; pipe nipples worked out quite well as spacers. Oh, I used a loonie on each piston crown so I would wreck the pistons (Loonies are $1 coins here in Canada. I put a whack of photos in to my folder in the Gallery, look for munkybarz pix.

 

[munkybarz]

Here she is after her 3 decade nap;

Cute Eh? How's this for a time capsule, that seat sure is bringin' sexy back ain't it?

I'll be pecking away on this one a while for sure.

Take care, -Bill

 

[CarlS]

Bill, that is a nice find. Yeah, that seat brings back some memories. Those were quite popular for a while. Very nice job on the jig. I will look at your photos.

I looked at the photos. and thanks for posting them. I have helped tear down motorcycles, vintage autos and tractors that sat out for 30 or mores in the weather. That is the WORST crank I have ever seen. My wife says you have your work cut out for you. :y114:

Do keep us posted on your progress.