Once lost lands and partially melted a JE piston in my Jota....no pinging but was massive mistiming due to a short on one of the original BTZ pickups. A pain when 1 bore damaged just beyond reuse....I got a new liner put in and so just one new piston same size as others. Ignition now Red Sachse .hope you can find the cause..
What happened to the Gap
- Thread starter Vince
- Start date
The Dyno run was done before the F1 cams went in,A11 at that time.These Kehan CV carbs started at 145 mains but ended at at 172 after the Dyno work.As I said the crowns were black carbon-ed,no real evidence of melting as far as I could tell but I am far from an expert.The reminisce of piston land was mashed into the top of the head on No 2,BTW that was a forged ceramic coated piston.Looks like No 3 happened sometime earlier,don't know where that bit ended up.On early inspection the bores have minimum damage.
chrisk
Hero member
- Location
- Brisbane, Australia
Well at least you know what it was, but unfortunately, that doesn't explain the shim gap closing. Shame it wasn't a valve or valve seat, that would have been a positive for Chris' theory.
Haven't pulled the valves out Chris,that shim clearance missing still isn't explained.The head was rebuilt with hardened seats about 5 years back.Clearances on the other 5 valves were reasonably close to OK.On no2 exhaust it has a bees dick of clearance left,was bloody close to spot on 4500ks back when the shims were done last.Thats shims in the 2.5 range give or take.
Considering the damage I have been bloody lucky to get it home under its own steam and isn't a hell of a lot more.
Considering the damage I have been bloody lucky to get it home under its own steam and isn't a hell of a lot more.
chrisk
Hero member
- Location
- Brisbane, Australia
FFS Vince, under it's own steam?So there's your problem, your water-cooled Lav project has been flawed by too closer piston tolerances. Stop re-inventing the wheel. Your name isn't Doug.
Vince shit sorry to hear, bugger that, really is a shame to hear. Looks like a breakfast run will be off the cards for a while unless you get the Pantah out. ( maybe a big breakfast Sunday is what you need at a time like this )
Well now we know why the plug gap closed up definitively, guess perhaps in hindsight we were being a little to optimistic in thinking that it had been dropped when fitted. Still it got you home and not via your trailer so that has to be a good thing.
From your description of the damage to me as the issue is in more than one of the cylinder and is around the inlet pockets of the pistons then it sounds more like you may have had a detonation issue more so than a lean mixture. ( Detonation not to be confused with pinging here ) Is the area around the failure on the pistons cleaner looking that the rest of the crown.
This might also explain why your clearances on this cylinder have closed up on the exhaust...
Have you got some photos of the damaged area's of the pistons you can upload.
Let us know if there is something we can do for you.
Have a spare set of barrel and pistons if you need something to keep you on the road for the interim or you can borrow the RGS if you need...
Well now we know why the plug gap closed up definitively, guess perhaps in hindsight we were being a little to optimistic in thinking that it had been dropped when fitted. Still it got you home and not via your trailer so that has to be a good thing.
From your description of the damage to me as the issue is in more than one of the cylinder and is around the inlet pockets of the pistons then it sounds more like you may have had a detonation issue more so than a lean mixture. ( Detonation not to be confused with pinging here ) Is the area around the failure on the pistons cleaner looking that the rest of the crown.
This might also explain why your clearances on this cylinder have closed up on the exhaust...
Have you got some photos of the damaged area's of the pistons you can upload.
Let us know if there is something we can do for you.
Have a spare set of barrel and pistons if you need something to keep you on the road for the interim or you can borrow the RGS if you need...
Hi Brett I have a flash drive of pics Will took,its to big to Email,I will have a look at maybe pulling a couple out and email them to you.Looks like the Pantah is back in action.I will bring the flash drive to the next club night for a chin wag.So whats the difference between pinging and detonation?I don't think it was lean and I think the timing was close to ideal and I don't think it had an air leak and I don't pamper it but I do have some mechanical sympathy.
Vince no worries can have a look on Wednesday night.
Thought had finished doing technical training today.. when the last of the student left but well as it is you here is a brief explanation of the differences.
Basically preigniton or pinking ( correct term for pinging ) it is when there is spontaneous combustion of the fuel/air mixture, before the spark ignites it, causes a more violent explosion. Basically the fuel air mixture is ignited before the plug fires. A characteristic "pinking" is often heard, due to the forces in the engine. A pinging noise on acceleration is a symptom of pre-ignition.
Detonation on the other hand is where, the spark ignites the fuel/air mixture, as it should. Detonation occurs after ignition and causes an explosion of the mixture, rather than a smooth burn. Detonation is different to pinging in that sometimes you cant hear any audible noise such as pinging which usually occurs under acceleration.
To me by what you said about the carbon deposits and where the damage is it does sound more likely detonation that pre ignition...
We were doing a post Morton in class today on a Diesel engine that had failed pistons due to detonation issues..
Thought had finished doing technical training today.. when the last of the student left but well as it is you here is a brief explanation of the differences.
Basically preigniton or pinking ( correct term for pinging ) it is when there is spontaneous combustion of the fuel/air mixture, before the spark ignites it, causes a more violent explosion. Basically the fuel air mixture is ignited before the plug fires. A characteristic "pinking" is often heard, due to the forces in the engine. A pinging noise on acceleration is a symptom of pre-ignition.
Detonation on the other hand is where, the spark ignites the fuel/air mixture, as it should. Detonation occurs after ignition and causes an explosion of the mixture, rather than a smooth burn. Detonation is different to pinging in that sometimes you cant hear any audible noise such as pinging which usually occurs under acceleration.
To me by what you said about the carbon deposits and where the damage is it does sound more likely detonation that pre ignition...
We were doing a post Morton in class today on a Diesel engine that had failed pistons due to detonation issues..
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Grant
Guest
What make of piston is it Vince?
AndyW
Hero member
I was always given to understand that the pinking noise was due to the collision of the flame fronts from the pre-ignition and sparked ignition burns.. Detonation being due to incorrect fuel octane rating and/or overheating.
I had a detonation problem in an MGB a few years back: didn't actually know it until a mate remarked how noisy it was in the car. This was after the leaded petrol was phased out. I put in a couple of litres of AvGas with the fuel and suddenly it was whisper quiet.. After that I put a little AvGas in all my old bangers...
I had a detonation problem in an MGB a few years back: didn't actually know it until a mate remarked how noisy it was in the car. This was after the leaded petrol was phased out. I put in a couple of litres of AvGas with the fuel and suddenly it was whisper quiet.. After that I put a little AvGas in all my old bangers...
tom3c75
Hero member
- Location
- Cape Town South Africa
Quite a good overview of detonation in the link below. Spark plug damage is noted as one of the detonation indicators.
http://www.contactmagazine.com/Issue54/EngineBasics.html
http://www.contactmagazine.com/Issue54/EngineBasics.html
Cosi
Hero member
- Location
- Kingscliff
Vince said:
Leaning out up high Vince, fucked my last motor on a 50k high speed run with sweetas, you cant hear it at 180 plus, Red has the dyno run sheet for that one, was the video paul posted up, unfortunately it was a little too late
I sympathise with you but also thought i'd put my 2 cents worth in. I don't know anything about Laverda Triples but all the nicely polished ones I've seen have more than a touch of blue on the centre cylinder exhaust whereas the outer cyclinders do not. This may suggest that this cylinder runs leaner and possibly hotter than others. This may suggest that if your fuel ratio was marginally lean then maybe it justs tips the centre cylinder over the edge???
It doesn't help the problem but maybe some investigation will stop it happening again.
Cheers
It doesn't help the problem but maybe some investigation will stop it happening again.
Cheers