Engine problems....The Return!

[blykins]

My pistons were Probe forged pistons...the sheet that came with them recommended .004-.005.

[simonjrwinter]

Just found this http://www.probeindustries.com/Instr...rs_pistons.htm from probe so I should be ok

[wilf leek]

Simon, oh no, not again!

Some thoughts:

1: Are the side-to-side clearances right on the big ends? Cylinder lubrication comes mainly from splash from oil coming out of the big end bearings - too little clearance between the two conrods on each crank throw can reduce this significantly.
If this is the cause, I think you may also find a small end gone bad somewhere - your knock.

2: The piston scuffing could also be from too little piston-cylinder clearance. It could be that although you had the bores sized right, you have the WRONG pistons. Measure some of them, assuming you can find one or two that are not badly scuffed, and mike the bores to see what ACTUAL clearance you have.

3: The loose rocker episode is a red herring - it did NOT cause the damage you are now seeing. Forget about it as a cause.

4: Did you have any signs of severe overheating? Running-on after turning off, pinking etc?

5: I am still not sure that your knock is coming from these pistons - piston slap varies greatly with engine temp. Did the knock change at all as the engine warmed through from stone cold?

6: Tell me EXACTLY what ring gap you set. Ring gaps are often quoted as so many thou per inch bore diameter - you have to multiply the stated figure by the bore dia in inches.

HTH

WIlf

PS - Anglo-American translations:

small end - wrist pin and bearing.
big end - big end or rod bearing
pinking - pre-ignition or pinging

[Ron61]

Wilf,

Thanks for adding the translation. Now all of us know what you said and not just 5%.

Simon,

Man, I feel for you. This has been a nightmare. Hope everything cleans up ok and your crank and block are ok.

Ron

[simonjrwinter]

Wilf,
Sod's law isn't it. If don't fix this I'm going to go out and buy a ch**y engine to put in the bloody thing.

1 the small ends all seem absolutely fine side to side. clearances..I'll check

2 The block was bored to match the pistons, although I have the block and pistons in my Renault at the moment and will be paying the machine shop a visit first thing

3 Think you're right there.

4 NO signs of overheating, ran the engine first with no thermostat to bring it up to temperature more gently (as advised by several people) for running in the cam. put thermostat in after that. engine had NEVER risen above 82 degrees on the gauge (Two BIG fans)

5 To be perfectly honest, after I refitted the rocker, started the engine and heard the noise, It never got hot again. I have only started it for a few seconds (no more than a minute) just to see if I'd cured the knock

6 Ring gap, don't remember now, but was VERY careful no to make it too small. Rings were filed to fit individual cylinders. When I'm rich and famous I'll be able to afford a supercharger and the engine was built with that in mind (probe recommended 30thou plus if using a "power adder") so the ring gaps were left a little larger than normal and the compression ratio no too high. However I will check the end gaps and report back.

Simon

[golfnutjetsfan]

Simon you have my greatest sympathy on your engine struggles. I can perhaps answer one of your questions, the damage your pictures showed can definitely be related to a knock. Just last week I replaced 2 pistons in a street driven 4 cylinder engine for a low knock at idle and on acceleration with just that kind of damage. I also found nothing else wrong with any bearings, rods or wrist pins. Two new pistons ( in this case stock size ) and a light honing of the cylinders cured the problem. I and my service manager believed this to be a lack of oil problem on this particular engine. good luck Frank

[wilf leek]

Simon - just one more thought. Was the block thoroughly cleaned down after machining? I mean several times, using ATF or similar on rags until every last trace of honing grit is gone?

Get your machine shop to measure those bores at several points down the bore - I wonder if you have tapered cylinders? Boring without deck plates can do this - the cylinders take up a different shape as the heads are torqued down.

Also, I would 'phone the piston supplier tech line to double check their piston/cylinder clearance recommendation. 3 thou sounds a tad light for forged pistons.

Now get this thing fixed - I wanna see you with a smile on your face at Stoneleigh!

[nanard289]

Hi Simmon,
According to your pictures, it seem that this dammage could be a piston over heating result. It can be the fact of an optimist ignition point or a too lean air fuel ratio. I think it appears on the hotest cylinder (no 5). This hypothesis could be confirmed by the piston top aspect and the combustion chamber. If it is light grey, it can be an over heating. Paradoxically, forged pistons (as I believe you have) are more sensible to the thermal variations (due to the alloy expand coefficient) than hyper pathetic piston (that are hyper siliced). An other point is the oil quality. Remember that for the first mileages with a new engine we have to use only mineral oil (no synthetic oil). Hi hope my humble point of view can help you.
Bernard

[GUMBALL UK]

Simon,

Any news yet on what the cause was?? Which machine shop did you use? was it Gosnays?

If you need a hand any evenings I can pop over.

Got to get you back on the road - wouldn't want you to miss Classic LeMans in July !!!

GUMBALL UK

[SFfiredog]

Simon,
Please check your bearing clearance at the fillet (cheek) of the crankshaft. Aftermarket cranks have very generous fillets, usually .125" If you used standard rod bearings without chamfering the bearing end at the fillet, the side to side clearance
on your con rods is next to nil. This clearance is critical to oiling the cylinder walls. I have seen this problem before.
Also, how cold did the engine run. I've seen wear patterns like that from engine temps that we too low causing too tight pistion to wall clearance when under a load.
Good luck,
Mike

[Junket]

My understanding is the problem is on the same crank throw SFS is correct on the after market cranks if one is bent with heavy weight oil could be a problem.
If you still have the rods on the crank check the side clearance at top & bottom of the stroke.
Ken