Piston/valve interface LM2...

[Dukedesmo]

So, just got the LM2 sorted for my preference; overhauled (& de-linked) brakes, new master cylinders, braided hoses, alloy brake pistons, reversed gearshift, rearsets, LM1 style fairing/headlight/simplified instruments, clip-ons, Lafranconis etc. and took it out for a good ride on Saturday.

Running beautifully and then when almost home I noticed a slight power loss, initially I put it down to fuel starvation due to possibly needing reserve as it was around that mileage.

Then I stopped at some traffic lights and it wouldn't idle but would still run OK so being just a few miles from home I persevered on, though I could hear a slight tappetty rattle from the left side.

Checked fuel, spark & plugs and all OK so I checked the compression; 155psi RH, 70psi LH. Took the LH rocker cover off and exhaust valve clearance had 'grown' by 0.3mm.

Anyway after much head scratching I took the head, cylinder & piston off to find this;



As you can see the piston has hit the exhaust valve. Damage that I can see so far is;

Piston dinged
Valve bent
Con rod bent (I think)
Push rod slightly bent

On disassembly the piston pin was very tight and I had to devise an extractor to get it out (long M10 bolt + various spacers) but the small end bush is loose and pushes out the rod by finger pressure.

Cylinder looks perfect and head appears to be fine, not removed the valve yet as I need to get a suitable spring compressor but it and, likely the seat, will be no good.

Not happy...     

[Vasco DG]

Valve timing system is controlled how?

[BigDave in PA]

The timing chain could be a factor. You didn't accidentally over rev the engine did you? Back in about 1980, a friend had a LM 1 and while street racing missed a gear. The engine over wound and floated the intake valves. I tore it down and had to replace all the valves. The pistons weren't marked like yours, in fact they hardly had a mark on them. The only parts it required were the valves, gaskets & O rings.

[John A]

Valve probly stuck and piston hit it.
If it were mine I'd send the heads to Mike Rich Motorsports for a port and dual plug conversion , really good work  I've always been pleased with the results

[Vasco DG]

MkII LeMans? So '81/82 so it's over 30 years old. Any service history? What sort of mileage? Any valve spring sitting, even if being used, is going to fatigue in 30+ years.

This is the thing. These machines are OLD now. If they have been maintained, overhauled and generally looked after they will still be great machines but most of them have been used as neglected beaters and denied maintenance at least at some point in those 30+ years. Is it any wonder they break?

Whip the valves out. You may well find a broken or fatigued spring.

Pete

[Chuck in Indiana]

^^^^^^ this.
Unkept's LeMans had a broken spring, but fortunately there were two, and the valves kept working..

[Triple Jim]

It looks like both valves hit the piston, so theories about a problem with a valve spring may be unlikely to be true.  My bet is the connecting rod is OK, but my bets don't always win.

[Dukedesmo]

MkII LeMans? So '81/82 so it's over 30 years old. Any service history? What sort of mileage? Any valve spring sitting, even if being used, is going to fatigue in 30+ years.

First registered in January '80, I have no record of any service history but only done 12,000 miles. Bike had very little use in the last 25yrs and none for the last 2-3 but was kept in very good, original condition as part of a collection in a warm garage.

Don't know the cause of the piston/valve clash, bike has no filters so could be a foreign object ingestion? Only the exhaust valve hit and the other cylinder seems fine (although not removed it) judging by compression and that it was running more or less OK for at least 15 miles even with the fault.

Springs look OK although I've not removed the valves yet as I need to get a spring compressor.

[Triple Jim]

Can you tell what caused the shiny spot on the piston on the intake side?  Or is that not what it looks like in the photo?

[kevdog3019]

If the valve can get hung up this could explain it. Look at the simple stuff first. If your rod got bent I'm guessing your cylinder would show some kinds of signs after 15 miles.

[Dukedesmo]

Can you tell what caused the shiny spot on the piston on the intake side?  Or is that not what it looks like in the photo?

Just an illusion/reflection from the machined pocket for the larger intake valve that side is fine, in fact the whole thing is OK now as I've cleaned & polished the piston and it's only showing a very small mark that I can live with.



Also honed/polished the piston pin hole so that the pins fits nicely so I'm happy the piston is good to go.

[Dukedesmo]

If the valve can get hung up this could explain it. Look at the simple stuff first. If your rod got bent I'm guessing your cylinder would show some kinds of signs after 15 miles.

This is the only encouraging bit because the bore is fine, no wear or scratches and still showing the original cross-hatching.

As far as the rod being bent, I can't determine if it is, if I try measuring sometimes I can get a reading that confirms and others not but it looks bent due to the way it's made as it has a bigger curve to the front (where it would be bent) also the pics I took make it look even worse due to the wide angle lens on my phone;



Plus it was at least 15 miles and I was still riding it quite hard during this time so you would expect some damage, as such I'm really not sure if it is bent or not?

[Triple Jim]

Maybe you can tip the bike and set the cylinder mounting surface level, using a bubble level, and find a way to get the level on the pin bore, like put the pin in and use two small V blocks for the level to sit on.

Or set the cylinder on and measure from the rod small end to the bore surface, front and rear.  Or both methods.

I'm still betting the rod is fine.

[Dukedesmo]

I'm still betting the rod is fine.

I'm certainly hoping you're right.   

[kevdog3019]

I can't imagine with the little ding in the piston and not actually losing a valve top to float around in the head that the rod would bend before the valve.  Path of least resistance says valve only bent (and likely pushrod).  You will get a better picture when you get those out.  Others will know more about a bump at speed and rods bending. 

edit: I like the measuring technique of top of cylinder to piston top all around.  Not sure you could just set the cylinder in is all to make it true??

[PeteS]

Another vote for weak valve springs. When Manfred did the valves on my 850 LM he put in stronger springs. I have over revved it many times and still have good compression.

Pete

[Dukedesmo]

Test fitted the piston with the barrel tightened down and it looks OK, goes up and down smoothly;





Doesn't seem to be tilted in the cylinder...

[Stevex]

it's only showing a very small mark that I can live with.

That could easily become a stress raiser; if it were mine I blend it out completely...but that's just the aircraft engineer in me speaking.

[Dukedesmo]

It'll soon fill with carbon deposits.   

Of course, if the rod is OK then I need to address the loose little-end bush. Don't really know if it got loose in this incident or if it was already so?

I'm guessing the only real solution is to fit a new/larger bush?

[Vasco DG]

First registered in January '80, I have no record of any service history but only done 12,000 miles. Bike had very little use in the last 25yrs and none for the last 2-3 but was kept in very good, original condition as part of a collection in a warm garage.

Don't know the cause of the piston/valve clash, bike has no filters so could be a foreign object ingestion? Only the exhaust valve hit and the other cylinder seems fine (although not removed it) judging by compression and that it was running more or less OK for at least 15 miles even with the fault.

Springs look OK although I've not removed the valves yet as I need to get a spring compressor.

With respect the fact the odometer says 12,000 miss means precisely nothing on a 30 year old bike.

Valve springs were always a bit of an issue on mid valve LeMans, that's the reason they were changed at some point in the mid eighties, it may of been with the advent of the Mk III I ant honestly remember. The fact is though it's still a very old motorbike with no history therefore making a diagnosis of what may of caused the problem, unless there is an obvious breakage, is going to be very difficult.

If it were mine I'd shout it a new set of springs and a full head service with K-Lines on principle.

Incidentally if you have honed the pistons so the gudgeons are a sliding fit you have probably buggered them. They are cast and are supposed to grab the gudgeons when cold. Forged pistons, as a rule, have gudgeons with a sliding fit. Cast pistons, generally require the piston be heated to allow installation of the gudgeon and they only loosen up at operating temperature.

Pete

PS I doubt the rod has been compromised.

[Dukedesmo]

Incidentally if you have honed the pistons so the gudgeons are a sliding fit you have probably buggered them. They are cast and are supposed to grab the gudgeons when cold. Forged pistons, as a rule, have gudgeons with a sliding fit. Cast pistons, generally require the piston be heated to allow installation of the gudgeon and they only loosen up at operating temperature.

Oops, if this is the case then it's too late as it is now a sliding fit. Only done the one as I've not removed the other head.   

[Chuck in Indiana]

That could easily become a stress raiser; if it were mine I blend it out completely...but that's just the aircraft engineer in me speaking.

Yeah, me, too.. but apparently it's a moot point after the piston was honed. 
Is it just an optical illusion, or is that rod twisted a half degree or so? At any rate, I'd do some serious measuring.

[Dimples]

Valve probly stuck and piston hit it.
If it were mine I'd send the heads to Mike Rich Motorsports for a port and dual plug conversion , really good work  I've always been pleased with the results

Might want to get a commitment from him first. These days Mike has the same reputation as Charlie. It can take more than a year for your heads!

[smdl]

Might want to get a commitment from him first. These days Mike has the same reputation as Charlie. It can take more than a year for your heads!

I assume you mean Charley, not Charlie!  I feel really badly about Charley Cole.  Great guy -- so helpful and knowledgeable.  I sure wish I knew what kind of difficulties he is going through.

Cheers,
Shaun

[Dukedesmo]

Yeah, me, too.. but apparently it's a moot point after the piston was honed. 
Is it just an optical illusion, or is that rod twisted a half degree or so? At any rate, I'd do some serious measuring.

Indeed, schoolboy error on my part means I'm looking at a new piston . Actually I am informed that it is not a standard piston, rather a high-comp so that further complicates things. 

As for the rod, I'm still a bit concerned so I'll remove the other side assembly for a comparison and it will be good to check/overhaul both heads anyway but I'm thinking the rod will have to come out for a definitive test and it probably needs to be out to press a new small-end bush anyway?

I'd rather do the job right even if it takes a bit more time & expense because I don't want to be doing it again this time next month/year...

[Vasco DG]

Aw Shit.

I thought the dome looked a bit high for a stock LeMans.

Do herself a favour, buy a new set of Gillardoni's. If you can't get the 83mm sets get the 88's and be done with it.

Get the rods closed and ground and if needed get a new rod and have the whole wretched lot balanced.

If it is an aftermarket 'High Compression' kit it will be asking for further problems with today's crappy fuel.

At the end of the day it's an ancient, obsolete, motorbike engine with no service history but obviously it's been 'Modified' back in the day. Thing is it's never going to win any races, or even traffic light Grand Prix in 2015 so why not just get it as good as it can be for today's conditions and fuels? If you go down that path you need a lower compression ratio, minor carburettion changes and a willingness to accept reality. Alternatively you can throw almost endless money at it for little reward and embroil yourself in a host of problems.

I'm not trying to dissuade you from pursuing the project. Just hoping to inject a small amount of reality.

Pete

[Rough Edge racing]

 If it were me I would be checking piston to valve clearance while the engine is mocked up using the common clay technique instead of just quessing...Just because the pistons appear to have a higher dome does not mean for sure the piston to valve clearance is less. Could be a combination of factors that stack up wrong like milled parts, thinner gaskets etc. Get to the cause before throwing in new parts...
 A worn timing chain will retard cam timing making piston to valve contact less likely.

[Dukedesmo]

Meanwhile I checked the RH cylinder;



The valve clearance is up by 0.2mm and the same thing has happened; piston to exhaust valve contact, maybe not quite as bad considering the higher compression and clearance not quite as far off but on this side but still requiring the same attention.

Arse...   

[Triple Jim]

It's looking like Rough Edge Racing's idea of checking clearance with clay is a good one, to see if the problem was only weak springs, or maybe a bad assembly in the first place, or both.

Or does your board name indicate you were trying to convert this to a desmodromic system?     

[Dukedesmo]

Or does your board name indicate you were trying to convert this to a desmodromic system?     

  now there's a thought.

Yes got to be a cause and needs to be found before filling it with new parts and buggering them up again.

Not sure how the timing system works with regards to tensioning etc. but it would seem like a timing issue to me. Regardless of suitability of HC pistons they have been in there a long time and I don't believe the valves met them until Saturday...