I'm curious too. Just pulled the cylinder on my 74 750 and I see the same thing. But it's really only evident on the primary side piston.

 

I’d call the smudge on the piston normal wear and not requiring replacement.

I can’t tell how deep the scratch in the bore is.

 

Primary side most prominent? ...will check mine...scratch up vertical center of bore can barely be felt with fingernail....nail does not catch it only can slightly feel 'something'..

Somewhere I seem to remember scuffs occurring on "thrust sides of pistons" or some such terminology...is it prudent to just clean everything up and put in new rings? Or just reinstall the old rings..

FYI wrist pins [gudgeon pins] only came out with heat and no movement when inserted into rod ends or pistons....

I am squeaky new at this....just wanted to check my sludge trap after 30+ years of sitting un-used and now redoing just about everything....frame, wiring, motor, wheels etc etc...ignorance may be bliss but it sure can create anxiety!

Thanks ...Phil

PS...Pistons are AE (Associated Engineering), also produced under Hepolite and later by Nural (Federal Mogul)...marked AE413 and 17844...'73 [J73] and on top of piston ID12 and +20...

 

That all looks usable. The sludge trap only blocks up with increased mileage so at 10,000 miles, should not need cleaning yet but fit an oil filter.

 

May not have mentioned but bike has not been started for 30+ years...hence my concern for sludge trap and possible hardening of oil/particles that could block oil feed to rods/bearings.

Would you recommend new rings? And while "de-carboning" the top end is recommended I could now find how that is recommended to be accomplished.

Purchased Andy's Tricor oil filter and will install when I reassemble the bike.

 

If your rings look good and have the right gap, re-use as a new set may not be a good fit requiring filing the gaps. I have some new Hepolite rings here where the rings were very oversized so used my old rings again. Decoking is just cleaning up the piston crowns carefully and not with a very sharp edge screwdriver etc. Small scrapes can be polished away though. The sludge in the trap is often very compacted and needing a hammer and chisel to get out. At 35,000 miles, mine was half full. I was changing the crank as it had snapped when riding at 80 mph.
As an un-used bike for that period, at least replace the crankshaft end seal in the timing chest cover before any riding.
That engine, when used in 1976 would have used an oil inferior to what we have now. During running in, the pistons have rubbed a little.
If you are going to strip the entire engine, check the main bearings very carefully as one i had that had been unused 6 years had rust on one ball in the main bearing. I missed it when building so when fired up, it made a noise and i had to build it again

 

Great advice and exactly what I need,,,will read up on how to assess if rings are good-to-go; need to purchase a ring compressor set to check ring gaps ....do you use a solvent along with say a plastic scrapper to remove carbon/coke? Yes, I plan on replacing all seals and bearings that I can...want the bike once back on the road to outlast me and at my age that will be a safe bet.... Appreciate all the help folks have offered.....I enjoy the challenge but want to get it right..

Phil

 

I use a strip of aluminium filed sharp at one end, it is softer than the piston alloy. I also have a 1/4' tube bit of copper flattened and filed sharp at one end, these work fine. I don't use a solvent, but generally emery using 800 grit then hand polish to finish. Cleanliness is next to godliness they say!
Ring gap is measured in the bore, no compressor needed.
Remove ring from piston [mark top of ring so you can install back correctly, texta or some such, but they often have a mark saying 'top'].
Place ring in corresponding bore, use piston to 'square' the ring up.
Measure ring gap.
Do this say 1" up, 1" down, and in middle of the cylinder. A good bore should give the same gap measurement or very close.
If the ring needs gapping [and a bigger gap than spec'ed is OK, a smaller one is a no no], use a strip of say 400 grit emery, fold it double so you have grit either side, then place it in the gap. Hold the ring in your fingertips, lightly compress the ring to the emery then gently drag the emery through the gap. Check gap again, repeat as needed. You can finish off with some 800 or better emery.

Note, there are files for this, but you don't need them.

 

You can used wide cable ties to compress rings when refitting the cylinders. Make sure the rods are held in place with a board then oil the cable ties which should not be too tight, then push down and the ties just go down so can be cut off. It takes very little time and i have never had a problem but best done with 2 people so one is guiding and the other is supporting the cylinders.
You will need a crankshaft pinion puller which is quite expensive and try and find someone who would lend you one but not that common to find another owner local to you.
These engines are fairly easy to rebuild if you already have a good knowledge of engines generally. You do need some mechanical skills or it will overwhelm you. Get the manual and parts book and maybe a Clymer manual to compare with a factory manual so you might get 2 views

 

Hi Phil,
I don't see anything alarming to me after 10,000 miles of service. Minor striations on the thrust surfaces seem like normal wear and should be able to be gently flex-honed. Maybe the cylinder walls were once scrubbed clean of oil by the introduction of petrol during an initial start-up with starting fluid, or a piece of carbon or unfiltered dirt entered the combustion chamber? I'd clean the pistons, hone the bores, check the piston clearances and fit new piston rings before deciding about a re-bore.
-Dave

 

Hi Phil, The AE pistons are old orginal that are usually genuine Triumph dealer sold oversize. Very high quality.


Personally, I'd blow the rings clean with compressed air, line up gaps in 3rds avoiding thrust faces. Oil rings, pins, pistons, bores well. Put back on. Rings will still seal well. I've done many like that.

Lots of ways to compress the rings. Trust me, if you can possibly afford it buy real ring compressor tools from Triumph vendor. Make a good stable level piston board. Especially if you must work by yourself. So safe & easy! Once you use them you'll never do it any other way. Shop around for best price. Not that costly.

Many use the ring compressor upside down. Don't put screws next to piston. Then they hit the cylinder. Put screws against piston board. Then the ring compressor fits right inside of the chamfer at the bottom of the cylinder. So rings stay compressed until they almost enter the straight part of bore. So easy.
Don

 

Hi
Ring compressors are great and cheap, but you will need a pair that split apart so they can be removed from around the con rod once the piston is in the bore.

The ones designed for cars and motorcycles that have crankcase and barrels integrated are designed for pistons being inserted from the top, they won’t work on your bike.

put tape on the front and rear edge of the con rods so they don’t bang against the crankcase, etc. Any marks even small ones will be a stress riser that weakens the con rod. Remove the tape at the last second before the barrels are bolted down.

Making a plate that rests on the stud barrels with cutouts for the con rods is a great help, the pistons rest on this square and solid until the rings are engaged, I made mine out of an old plastic kitchen chopping board.

Research posts on this forum sealing/fixing the cylinder base suds.

I would replace the rubber based components after all this time, especially the tappet block seals, exhaust camshaft points seal and the crankshaft oil feed seal.

With the piston rings, I run a diamond file across the outer tip of the rings where the gap is, and just blunt the sharp point very slightly, so that it does not dig in to the bore and leave a score line.

Regards
Peg

 

Plastic cable ties rule. Nothing to damage the rings and just snip off with sidecutters. I threw ring compressors away years ago as they were just not worth the time using them.
My next challenge is the cable tie fitting of a rear tyre in the Spring. About 6 cable ties needed but i have plenty. Always keep cable ties with your bike, they will even hold up the exhaust if a fixing goes missing.Best repair gadget ever made.

 

Hi Geoff,

used wide cable ties to compress rings when refitting the cylinders

Nothing to damage the rings and just snip off with sidecutters.

Tch, think of the environment! Use reusable ones ...

Regards,

 

Good advice and appreciated.....still do not know where the "thrust surfaces" are and why they exist....I am enjoying the process and came across something today which vindicates my decision to get into the motor...primary chain was not loose nor too tight but the damage in the stud in this photo was scary to contemplate if it had snapped off...assuming the chain should be replaced along with the tensioner; unless I can verify that when motor was rebuilt in '76 at TT Motors Berkeley they put in a new primary chain and "overlooked' the damage to the stud, unlikely....studs for the stator are unique to '69-72 only, ordered a set [only located at CBS]...another surprise was the CEI nut on rotor [15/16 SAE worked]; when nut finally came loose it brought the stud out of the crank end and seemed welded to the stud...replacing both...another oddity is that the primary chain oil line was missing....sure I will find more to fix or replace! Rambo, no need to clean out sludge trap when I finally get there...putting in a new one...with a hex cap...Peg, rods wrapped in foam pipe insulations and cylinder studs all capped with old garden hose sections...still trying to visualize the plate you and TR7 recommended. 

Thanks all, you folks are great.

Phil

 

Try a Renolds primary chain. I found they last a lot longer than any other make i have bought. One less expensive chain lasted just 4000 miles before rollers were breaking up.

 

Hi Phil,

do not know where the "thrust surfaces" are and why they exist

Because a piston's motion is linear but the crank's motion is rotary, the connecting rod is at an angle to the piston's motion most of the time; then the conrod "thrusts" the piston towards the side of the bore closest to the piston end the rod.

studs for the stator are unique to '69-72 only

Not sure I'd call a part fitted to several thousand engines for five model years (they were also fitted to early '73 650 twins that had duplex primary chains) "unique" ...

another surprise was the CEI nut on rotor

Not really, the crank was the same pre-'69. The threads in the cylinder block for head bolts and studs also remained CEI on all 650 and 500 blocks 'til the last of both ranges in '74.

another oddity is that the primary chain oil line was missing

According to previous posts both here and on BritBike, they come loose regularly, don't serve any useful purpose when in place so many builders don't fit 'em.

clean out sludge trap when I finally get there...putting in a new one

That's actually what "clean out sludge trap" means ... old ones don't survive removal so a new one is fitted. Be sure the new one's hole for the locating flywheel bolt lines up with the crank hole and, given the parts makers' finely-honed ability to make things incorrectly, check as far as possible the new sludge trap's oil holes also line up with those in the crank.

Peg,
trying to visualize the plate you and TR7 recommended.

Peg meant "rests on the barrel studs", as in those screwed into the crankcase around the opening, that poke through the base of cylinder barrel when that's fitted on the crankcase. As well as providing a surface for the pistons to rest on when the barrel is pushed over the pistons and rings, the plate prevents small parts falling into the crankcase.

Hth.

Regards,

 

I've cleaned out and replaced several sludge traps, they aren't all destroyed on removal. In fact most can be cleaned and reused if you use the right extraction technique.

Its your call whether you use the oversize bolt/thread tap and spin it out, or use the threaded rod and grub screw and pull it out by using a hollow tube spacer and a nut on the rod. In both cases a warm crankshaft is better than a cold one!

 

Making a plate that rests on the stud barrels with cutouts for the con rods is a great help, the pistons rest on this square and solid until the rings are engaged, I made mine out of an old plastic kitchen chopping board.

ring compressors that open, as described. Piston ring fitting tool, ensures the ring is spread square and does not twist and ruin the rings sealing edge, base board, made from an old kitchen chopping board to rest the pistons on so you can insert them in the barrels easily (the board would be better if it was thinner), the cut out slots are to clear the con rods, the alternative is to grow a second pair of arms.

 

Good board Peg, i used plywood and have kept it for another time. Plastic would be better as no splinters to drop down. That tool in the middle is for holding a beer can so your fingers dont go cold but could be used to fit rings i suppose

 

Another download of practical and needed information...thanks! Wife is going to be pissed when I cut up her cutting board.......but the use of such a plate/board makes total sense, unlike sea stars, growing another set of arms ain't happening ...I now plan not to remove rings and reuse pistons after a clean-up and same cylinders; so far small end bushings and gudgeon pins seem good to go, no play or scoring ...yes will purchase opening ring compressors...

What fluid/solvent does anyone suggest using in cleaning pistons/cylinders or "washing" internal parts and pieces? Stoddard's?

Next stop...removal of sprocket and then removal of clutch 'etc'.... yes, I bought the pullers...

This is getting interesting! Need to take my time and not screw it up.........

Phil

 

Rambo....white spirts, mineral spirits and a combo Stoddard solvent are all about the same here....I have them and will use them...thanks...going off script but we drove along southern tip and then up west coast...Dún Aonghasa, Doolin and especially Skellig Michael were breathtaking and made me appreciate what was important....wonderful folks and great heritage...with or without St Patrick.

Pretty sure when +20 pistons installed new pins went with them...and judging from small end bushings they were replaced then...when I finally get to big end of rods I have plastigauges at the ready...

Since I opted to paint my frame and pieces, cleaning and perhaps a light sanding will chew up a lot of time....not going for show but go....still want to do a good job.

Thanks,

Phil