Identifying a rattle

[K1100]

Blimey. I've just inspected the bores again in the light of what you and Muskrat say, and I can't see anything that looks wrong except on the very top lip of the bore, a tiny mark that corresponds with the mark on the edge of the piston... as if something got caught there. Is it possible that  a piston can seize without you noticing, and without damage to the bore? I'm a bit out of my depth here! I've also looked hard at the valves and there's nothing missing there ... no chips....

[trevinoz]

If you were riding the bike, you would most definitely feel and hear the seizure.
If you pull the clutch in in time you don't lock up the back wheel.
Did you have the engine rebuilt or is that how you got it?
Have the bore accurately measured and compare it to the piston size as it was, not as it is.

Trev.

[K1100]

Hi Trev. That's how I got it. I've done about 300 miles since buying it last summer, and the paperwork shows it had a rebore and much other work by SRM in 2002, 11,000 miles ago. I'll do some measuring tomorrow.

[trevinoz]

I suppose it's too late for a warranty claim!   

Trev.

[KiwiGF]

As per prior post inspect and measure the bore to see if its worn and needs a rebore. After a seizure it's possible for the piston to barrel clearance to increase  - it happened on my engine - I'm not sure why  this happens - maybe the piston gets "compressed" when its hot and seizes and then has the increased clearance when it's cold. In other words you may not be able (after a seizure) to tell if too tight a clearance after a rebore was the cause, I personally doubt it after 11,000 miles, more likely lack of oil, timing or mixture issues?

[muskrat]

 It may have ingested a bit of crud that caused the mark/chip that may have started the ball rolling. A seizure like that would have marked the bore, that's why I think it may have been honed and the pistons re-used maybe with new rings.
When a piston nips up material is literally torn off the surface hence more play/clearance when freed.
Trev, that's a mild one compared to a few of mine NIPPING up at 8000 RPM.
Cheers

[K1100]

I'll stop smiling when I have to start paying money to put this right but at the moment I'm enjoying the detective work. I took the barrel and piston to a bearing and boring specialist this morning - waiting to hear about measurements and whether a rebore is necessary - but he says that from the appearance of the piston the cause is a lack of lubrication, not overheating or tightness, and most likely cause is fuelling/carburation issue - that something has caused oil to be washed out of the cylinder.

So now I'm wondering, is that because the bike spends most of its time on the side stand?

[bsa-bill]

Left hand side - is that left as when sitting on the bike?
if so then historically this is the side most likely to overheat, of course lack of lubrication and overheating do go together like love and marriage, so your man might have a point.
Opinions differ as to why BSA introduced the small hole in the left hand conrod that squirts oil up into that cylinder, I know I read that it was to address overheating problems on that side.
Have a look down that side see if the hole is there, it's on the side of the rod that faces the middle of the crankcase.
It could also be that oil pressure has dropped on that side as it fights its way through a partially full sludge trap, only one way to find out I'm afraid and that's to go the whole way and strip the engine down, you half way now anyway and you don't want to put it all together and the same thing happen.

all the best - Bill

[RichardL]

Muskrat's thought about pistons reused after a rebore might explain the apparent excess clearance now existant.

Richard L.

[K1100]

The bores are +40thou, and are +2 thou over that.

So I've bought a pair of +40 thou GPM pistons which I'm told are about 7:1, and new bushes.

I imagine the next problem will be how to ream the bushes with the engine in place. Has anyone any experience of that?

Bill - I have discovered the drilling you mentioned... tiny! The sludge traps were cleaned 11,000 miles ago so I'm going to assume they are ok.

[metalflake11]

Has anybody mentioned the reason this has happened yet? It would be awfull to buy new parts only for the same to happen again. In the wrong hands even the most proffesional work can be ruined in 12 years and 11,000 miles, assuming that is the true mileage. If muscrat is right about used, and previously siezed pistons being used in freshly bored cylinders then I would start  investigating further into the engine. I'd start by looking for job numbers etched into the casings, phone S.R.M. and they will tell you what was done. Hopefully they will confirm  the sludge trap was cleaned etc etc. The washed out theory might be right, but were those pistons in those barrells when it happened? Or were they used because they were better than the origionals which could have been destroyed? People do stupid things, and will then pull awfull stunts to recoup their money. I know a really top class mechanic who fitted a wooden piston made from a old table leg into a car just to get it running on 4 cylinders, to get it through an auction for somebody. He did it because he could and he thought it was funny. It worked, but what the new owner made of it we will never know.

[bsa-bill]

The sludge traps were cleaned 11,000 miles ago so I'm going to assume they are ok.

Please don't think I'm a glass half empty character but I do hope your assumption is correct, this mileage would be well within the scope of a well maintained bike that's had regular changes of oil so if you know that for sure that's fine.
If not then some kind of re-assurance would be to check oil flow through, the crank not sure how you would do this (others please comment)  I'm thinking along the lines of removing the pump and squirting oil into the pressure gallery and see it come through the crank and hopefully at least a seep through the mention hole.

7:1 pistons - a good choice, I have a rocket type bike on 8.5 and a Flash on 7.1, while the Rocket is fun to ride with a bit of spirit the Flash is a civilised, reliable and smooth beast in comparison.

hope it turns out good for you

[K1100]

The replacement pistons are on order (GMP +60 thou) and the barrels are booked in for re-boring. Expert advice was not to put the same size pistons back in (+40 thou).

Meanwhile I will find  way of checking that oil flows through the hole in the con-rod (thanks for that advice Bill ...), and I have spoken to SRM who confirm that they did all the work - including needle roller conversion - in 2002.

SRM couldn't supply the pistons - they only have high-compression pistons, which I didn't want.

The next step of this ever-growing challenge is the small end bushes. On the side of the damaged piston there is play - the old gudgeon pin rocks in the bush. So new bushes are on order but how to ream them? The idea of having to strip the engine right down to remove the con-rods makes me feel ill!

[muskrat]

G'day K1100, good to here your doing it right.
You can replace the LE bushes insitu. I use a deep socket and threaded rod to push the old one out with the new one. Sometimes you can be lucky and not have to ream them but if you do it would only be a couple of thou. I know it's not really the done thing but I have used a small cylinder hone to do the job. Ideally the rods should be removed and line reamed.
Cheers

[K1100]

The issue of reaming without dismantling the engine seems a tricky area. Stripping the engine right down to remove the con-rods is obviously the  proper way. But I am very reluctant to take the crankcase apart because everything in the crank/camshaft department is in good order. I am not sure my skills are up to putting it all back together

I found this on a Scott website as a guide to reaming:

"Once the bush is in place, a small amount will need to be cleaned out due to shrinkage. Do this by tapping the reamer into the hole with a light blow with a mallet. Turn the reamer half a turn, and repeat the process. Aim to get the reamer through as quickly as possible. DONT do the obvious trick if spinning the reamer round like a propeller - you will just get a tapered hole. Don't worry about scratch marks from the reamer, and dont make the bush too tight otherwise it will pick up. No need for  lubricant - the object is to remove material."

I can buy an adjustable ream for about £55 and I think the two challenges will be (1) keeping the reaming of both bushes in line and (2) keeping swarf out of the crankcase.

Or should I bite the bullet and send the bottom half off to SRM for them to do the job?