Britbike forum Forums Thread Like Summary - T140 Cylinder Scoring

What would cause this vertical scoring of the cylinders? I had the engine stripped down for inspection last winter. Cylinders were within spec so they were honed and new Hastings rings installed. The bike has gone 500 miles since the new rings. It starts easy, runs smooth and does not smoke. The problem is that it is using alot of oil. Consistantly using 16 oz, every 100 miles!

I thought maybe the top two rings were upside down so I pulled the cylinders this morning and this is what both cylinder walls look like. The rings are installed correctly with the dot on top and the taper facing up. Before pulling the cylinders today. The compression was 60 cold and 125 hot, and both cylinders within 1 psi.

I would have said it looks like the oil control worm ring being too long and scoring the bore. Check your worm ring for shine on the high points.

Did you gap your rings prior to install?

BUT...there are some marks higher up, not many, but some. So it has to be grit or hard carbon bits breaking away.
You also have a ring in your bore about 3/4 or the way down...what is that from??? Its usually where you have water in the bore and let the piston settle in the one spot for a few weeks while the water rusts the bore?

John, thanks for that.

Bob’s pistons don’t look anything like that though.

I have no difficulty with your description of detonation/overheating symptoms, but I don’t see it obviously relevant in this case.

Bob’s is a situation where the new rings (with a new hone) haven’t really had a chance to bed in properly.

For whatever reason, the worst bore scoring that I have seen (in my limited experience) has apparently happened in only 500 miles.

The (hopefully survivable) evidence of partial seizure on one piston only doesn’t explain the massive scoring on it’s own. Such marks on a piston, while not desirable, are not uncommon, and I’ve never associated them with massive scoring of the bores.

If you look at the pics of the bores John, I think you will consider the sealing of the rings almost irrelevant. How could the rings even pretend to seal against such a surface?

Bob -

I have a thread on this exact subject from about 10 years ago. You can read it here:

https://www.britbike.com/forums/ubbt...-about-inner-stud-orientation#Post310431

In short: Outer 3/8" studs go 'tit' down. you want threads showing at top of cylinder. Pay attention to the ball bearing mentioned in the thread. Don't pre-tighten studs. Finger tight will do.

Be sure two 5/16" inner studs are installed with the longest threaded portion down.

Cheers,

Steve

It was the 4 inside 3/8" studs that were installed the wrong way by Triumph. The 5/16" studs are installed correctly. The practice of having a stud bottom in the hole was noted in his writings by Phil Irving. The practice was re-introduced in 1971 by Umberslade Hall and you can clearly see it on the 1971 and latre BSA A65 head studs. At least BSA has different threads at each end so you cannot put it in upside down.

Attached Images

Which tells me that the head was over grossly over torqued at some point. To me... it illustrates the need to not only stick to the recommend torque using a decent torque wrench that was stored properly and calibrated within recent history, but to use torque plates when boring/honing cylinders. If you haven’t..... have a look at MM’s Clipper thread. Completely different setup, but it gives you an idea how how much distortion can occur. A lot! And he wasn’t over torquing things. As I mentioned before, that photo (showing the blow by at the top) goes a long way to explaining what went on here. Not the whole story, but the majority of it.

So basically what I’m saying is regardless of how the studs were installed you’d still see evidence of distortion there (around bolts and studs) just from being over torqued or bored without torque pates (plural).