Preventative measures.
Discussion
Hello all thought I would post this up. As many know I had the engine removed to sort out a big end shell bearing. As always it’s good to know why this damage occurred.
Now to the point of this post, the chaps tasked with the work where certain I had suffered from detonation, only on one cylinder so the culprit was found to be an injector not working to its full capacity.
Makes sense really, not enough fuel to create a cooling charge, compressed and igniting before the plug fired. The resulting impact smashing down damaging the shell bearing, the big end of the connecting rod and marking the crank journal slightly.
I looked back for threads from other owners who had suffered the dreaded clack clack noise. Particularly Fubars as we seemed to suffer much the same symptoms.
One detail that stood out with Nick’s rebuild was scoring to the skirt of his piston(s), this I discovered would result from detonation as well, as the heat is dissipated into the piston without the cooling effect of the right amount of fuel, the piston swells and the scoring on the skirts being the tell tale sign. I notice Nick has now mentioned his injector(s) are maybe playing up. I must point out I am only thinking out loud, and am sure his garage know a hell of a lot more than I do about engines.
So is it worth adding injector checking and cleaning as a yearly check, It could have saved my engine from coming out for a fix, I am certainly going to be doing this as for around the one hundred pounds mark it seems worth while.
Would it also be wise to up the injectors to a higher flow rate so as not to bring them so close to their max output, I have the black bosche ones, no coloured ring.
Incidentally my car seems to have different conrods, not h beam or anything like that, but they couldn’t be sourced, so had the rod fixed, also my car has wasted valve stems, this could be seen by looking into the inlet ports. Just shows they are so different inside.
Any way what do you chaps think, worth while or what?
I notice another engine has developed the ticking; clacking noise will be interesting to see what has happened.
Nick.
A couple of points:
I'm sure someone cleverer than me will correct me, but what you describe sounds more like cylinder overheating due to running lean (combustion temp rises as the fuel ratio falls). Perhaps causing det subsequently, but that's somewhat beside the point. "The cooling effect of extra fuel" is somethign that's only generally used in turbo engines to keep combsution temps down - in na engines you want to run as close to stoichiometric (sp?) as possible (i.e. 14.7:1). Wacking in more fuel just loses power and screws up your emissions.
I don't know what the duty cycle of the standard injectors is, but if its below 80% (and I can't imagine they'd spec anything less), then there's no benefit from going for a bigger injector. It's no less likely to fail, and will probably provide inferior spray/atomisation/control.
If you're worried about flow rates drifting over time, then measuring exhaust manifold temps is perhaps an easier way of checking general health than flow-testing the injectors every six months or whatever. Maplin sell a laser therometer for about £30 and its reasonably accurate to 5-600C. If you find more than 5-10% difference between exhaust ports, then time for deeper investigation.
I'm sure someone cleverer than me will correct me, but what you describe sounds more like cylinder overheating due to running lean (combustion temp rises as the fuel ratio falls). Perhaps causing det subsequently, but that's somewhat beside the point. "The cooling effect of extra fuel" is somethign that's only generally used in turbo engines to keep combsution temps down - in na engines you want to run as close to stoichiometric (sp?) as possible (i.e. 14.7:1). Wacking in more fuel just loses power and screws up your emissions.
I don't know what the duty cycle of the standard injectors is, but if its below 80% (and I can't imagine they'd spec anything less), then there's no benefit from going for a bigger injector. It's no less likely to fail, and will probably provide inferior spray/atomisation/control.
If you're worried about flow rates drifting over time, then measuring exhaust manifold temps is perhaps an easier way of checking general health than flow-testing the injectors every six months or whatever. Maplin sell a laser therometer for about £30 and its reasonably accurate to 5-600C. If you find more than 5-10% difference between exhaust ports, then time for deeper investigation.
Yeah I am with you on that, I guess that is what I meant sort of, fuel leans out due to injector underperforming, lean mix ignites easier than than correct mix. Especialy under high compression, as with my engine, so igniting before the plug fires, that's detonation is it not? come on Jules what do you think. Oh this comes from the chaps that SP use, these are the guys doing the Wilder stuff, so know what's what.
Nickccc said:
Yeah I am with you on that, I guess that is what I meant sort of, fuel leans out due to injector underperforming, lean mix ignites easier than than correct mix. Especialy under high compression, as with my engine, so igniting before the plug fires, that's detonation is it not? come on Jules what do you think. Oh this comes from the chaps that SP use, these are the guys doing the Wilder stuff, so know what's what.
A lean mix is harder to ignite Nick. If you're running lean then you tend to burn out exhaust valves, as the mix will still be burning as the exhaust valve opens. For pre-ignition, you need something else that's got hot from previous in the cylinder, a carbon deposit for instance, the edge of the head gasket etc. If you have a slow burning mix, then some parts of the mixture will be heated up and pressurised enough to explode, before the flame front reaches them. This is detonation. Steve.
Edited by Steve_T on Thursday 13th March 11:40
trackcar said:
What they describe is entirely probable .. flow rate drops off, cylinder runs lean, spark plug tip or other part of chamber glows and ignites next fuel prematurely etc etc .. have you decided what you're doing next ref injectors/ecu .. I have an idea if youre up for it?
Tell me more,So far had injectors cleaned and tested engine sorted, just got to to pick it up.
Hi Nick 
I hope to give more indepth info on my rebuild as soon as its all working properly and Paul gives me a run down on what went wrong and what was put right.
(I know you guys like measurements and all the technical info...Im just happy if the b
d starts and gets me home again 
)
I will say, from memory, 3 pistons had the scoring and the reason the car hasnt come back from its post rebuild service is that Paul found a problem with 3 of the injectors
and we are waiting for new ones to arrive. Then we can finish the remap and get the old git on the rollers (buns at the ready chaps? )
Oil useage has gone from 1 ltr/6-700 miles to having covered the 1000 running in miles without the level moving off the full mark
Wonder how many years it will take to recoup the rebuild cost in lack of oil useage?
I hope to give more indepth info on my rebuild as soon as its all working properly and Paul gives me a run down on what went wrong and what was put right.
(I know you guys like measurements and all the technical info...Im just happy if the bd starts and gets me home again )I will say, from memory, 3 pistons had the scoring and the reason the car hasnt come back from its post rebuild service is that Paul found a problem with 3 of the injectors
and we are waiting for new ones to arrive. Then we can finish the remap and get the old git on the rollers (buns at the ready chaps? )Oil useage has gone from 1 ltr/6-700 miles to having covered the 1000 running in miles without the level moving off the full mark
Wonder how many years it will take to recoup the rebuild cost in lack of oil useage?
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