Is this detonation damage?
Discussion
Some of you will have seen the recent unfortunate meltdown on my Rover k-series turbo that resulted in a melted piston ("stuballs BRM build thread"). I never really found a cause and whilst dropping the head and block off with my engine builder of choice for the rework today we cleaned the cyl head off and had a closer look.
As you can see from the pictures below the cylinder head has some pitting on the squish pads - I didn't notice this before. Builder confirmed this is det damage and put it down to bad mapping. He thinks the failure is a combination of det and just weak pistons.
Thoughts?
As you can see from the pictures below the cylinder head has some pitting on the squish pads - I didn't notice this before. Builder confirmed this is det damage and put it down to bad mapping. He thinks the failure is a combination of det and just weak pistons.
Thoughts?
stevieturbo said:
But there are also pitting marks outside the fire ring too....
some better pics would be helpful, and of pistons etc.
You don't have to look far.some better pics would be helpful, and of pistons etc.
Stuballs said:
Update time
Ring land has broken away on 1/4 of the piston on the exhaust side. If you look at the inlet side, you can see where the very thin portion where the valve cutout is has started to bend in. this is obviously the original point of failure.
Whilst the other pistons appeared ok, closer inspection reveals that this is happening to all of them.
Ring land has broken away on 1/4 of the piston on the exhaust side. If you look at the inlet side, you can see where the very thin portion where the valve cutout is has started to bend in. this is obviously the original point of failure.
Whilst the other pistons appeared ok, closer inspection reveals that this is happening to all of them.
Thanks for the input guys. The markings outside of the fire rings are black residue from the resin (or whatever it is) of the mls head gasket. The pitting is definitely confined to within and near the fire rings and on the squish pads of the combustion chamber. Valves ok. Pistons all ok except for the one that melted and even that had no pitting anywhere.
I just thought I would get some other opinions before I went back to the mapper.
Thanks again.
I just thought I would get some other opinions before I went back to the mapper.
Thanks again.
Those valve cutouts were far too close to the top ring groove and the sliver of metal left outside of them far too thin (for their height). If they'd been machined down a bit to leave a shorter stubbier more robust sliver it would have obviated some of the problem but you really need pistons with the ring grooves lower down. However it was det that started the failure.
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Something caused the det, that is the question. Doesn't have to be the mapper though. There's certainly been a lot of cylinder pressure in there. I'd be open minded about this. Agree with the comments above about the valve cut out being at the edge of the piston. That was a failure waiting to happen.
It's very simple. If the cylinder head has det marks on the other three chambers where the piston didn't blow up then it's bad mapping that caused the det. If only the chamber where the piston blew up has det marks then the piston probably broke first from the valve cutouts failing.
Whoever put valve cutouts that deep and that close to the edge of the piston could do with being warmly shaken by the throat though and made to go and sit on the naughty step while he reads some good books about how to build engines properly. I find it hard to believe that a turbo engine with what is presumably a stock or at least fairly mild cam needed cutouts so deep in the first place. If the cutouts really did need to be that deep to clear the valves then it was the wrong choice of pistons!!! Either way it's the engine builder's fault. Hand in pocket time.
Whoever put valve cutouts that deep and that close to the edge of the piston could do with being warmly shaken by the throat though and made to go and sit on the naughty step while he reads some good books about how to build engines properly. I find it hard to believe that a turbo engine with what is presumably a stock or at least fairly mild cam needed cutouts so deep in the first place. If the cutouts really did need to be that deep to clear the valves then it was the wrong choice of pistons!!! Either way it's the engine builder's fault. Hand in pocket time.
FordPrefect56 said:
It's very simple. If the cylinder head has det marks on the other three chambers where the piston didn't blow up then it's bad mapping that caused the det. If only the chamber where the piston blew up has det marks then the piston probably broke first from the valve cutouts failing.
Whoever put valve cutouts that deep and that close to the edge of the piston could do with being warmly shaken by the throat though and made to go and sit on the naughty step while he reads some good books about how to build engines properly. I find it hard to believe that a turbo engine with what is presumably a stock or at least fairly mild cam needed cutouts so deep in the first place. If the cutouts really did need to be that deep to clear the valves then it was the wrong choice of pistons!!! Either way it's the engine builder's fault. Hand in pocket time.
It's not that simple.Whoever put valve cutouts that deep and that close to the edge of the piston could do with being warmly shaken by the throat though and made to go and sit on the naughty step while he reads some good books about how to build engines properly. I find it hard to believe that a turbo engine with what is presumably a stock or at least fairly mild cam needed cutouts so deep in the first place. If the cutouts really did need to be that deep to clear the valves then it was the wrong choice of pistons!!! Either way it's the engine builder's fault. Hand in pocket time.
If the engine ran for 1, 5, 10, 100k miles fine and then there was a problem. It could be fuel supply, fuel type, or other mechanical/install issues that lead to improper running and/or detonation. Then it is not just actual mapping fault..
But we'd need to know the history and as said have some detailed logs of when this incident occurred.
stevieturbo said:
It's not that simple.
If the engine ran for 1, 5, 10, 100k miles fine and then there was a problem. It could be fuel supply, fuel type, or other mechanical/install issues that lead to improper running and/or detonation. Then it is not just actual mapping fault..
But we'd need to know the history and as said have some detailed logs of when this incident occurred.
I agree that if it had been running fine for ages then clearly something in the calibration has changed which may well be outwith the responsibility of whoever originally set it up. Anyway noting the OP's remark that there's a build thread somewhere I ran a search and found this.If the engine ran for 1, 5, 10, 100k miles fine and then there was a problem. It could be fuel supply, fuel type, or other mechanical/install issues that lead to improper running and/or detonation. Then it is not just actual mapping fault..
But we'd need to know the history and as said have some detailed logs of when this incident occurred.
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Very interesting. The pistons are shown on the first page alongside a set of stock K series turbo ones and clearly the valve cutouts are way deeper than necessary. It appears these pistons were "designed", if I can use the term loosely, by someone, made by Wossner to the specs given to them and no one in the chain of supply gave the proximity of the cutouts to the ring groove or how thin the material outside the cutouts was any thought. However a set do appear to have been running in someone else's engine ok.
This engine blew up on the rollers so I think that answers your point above.
Having read through the entire build thread I'll stick with what I said above. The pistons are clearly horribly designed but det started the problem. Now it may well be that it was only det in that one cylinder due to a dodgy injector giving a weaker mixture or something else but pistons don't buckle like that unless there's massive cylinder pressure occuring. I'd love to see some good pics of the other combustion chambers in the head to check for det.
Anyway it's a shame because the OP clearly has engine knowledge and put a great deal of time into this but as I've always said, it's not what you know that catches you out, or even what you know you don't know because you can look that up. It's what you don't know you don't know and if a set of pistons with cutouts like that had come my way when I was building race engines for people I'd have stuck them straight back in the box.
The pockets are always a problem on the K series as the crown height is minimal and the ring pack narrow. On the stock K series turbo piston the pockets are shallower than on the regular piston as the shorter rod places the piston 2mm further down the bore and clearances are less critical. With the limited duration and overlap of turbo cams it might be possible to run with no pockets since the pistons will be 3.5mm below the deck height at TDC and the gasket is 1.5mm thick. This will give in excess of 4mm clearance at TDC, typically lift at TDC with turbo type cams will be less than 2.5mm.
Dave
Dave
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