Big end shells
Discussion
I have just had an engine rebuild pistons rods crack etc and when it was getting set up on the rolling road No 1 big end bearing let go. This resulted in a new crank and 1 new rod. had it fixed and within 2 hours the same thing has happened again. The car has gone back to the engine builder to get done again.
Any ideas what would cause this to happen ?
Any ideas what would cause this to happen ?
If it was that bad...how long was the engine run after it started knocking ?
Are all oil galleries totally clear ? Has air or fluid been pumped through to test them before the crank was installed ?
Could someone have fitted a wrong bolt somewhere, that is blocking an oilway ?
Are all bearing shells correct, and aligned so that oil can flow to the relevant parts ?
Are the crank drillings clean ?
Are all oil galleries totally clear ? Has air or fluid been pumped through to test them before the crank was installed ?
Could someone have fitted a wrong bolt somewhere, that is blocking an oilway ?
Are all bearing shells correct, and aligned so that oil can flow to the relevant parts ?
Are the crank drillings clean ?
The first time it happened I think the engine must have ran for a while as I left the car with the garage and it was on the rollers.
This time it was shut off staright away after there was a plume of smoke from the crank cae breather and it started to knock.
I have been informed the all oil ways were clear and everything was assembled correctly.
This time it was shut off staright away after there was a plume of smoke from the crank cae breather and it started to knock.
I have been informed the all oil ways were clear and everything was assembled correctly.
You need to rebuild with a new rod, and regrind the big end pin(s).
Do not underestimate the need to lap the crank, it removes the microscopic saw teeth that will chew the bearing up, and remember it is crank direction dependent. Consult your machine shop if you have questions.
I would use a countersink on the oil holes then a half round file to make sure that there's no chance of the oil hole picking up the bearing, and use a long twist drill to clean out all of the swarf that will have collected in the crank during grinding. Blowing out simply won't cut it, unfortunately.
You also need to clean out all the block galleries in a similar way.
Once the bearing is ground I would use plastigauge to check the bearing clearances.
Use very thick oil to build the engine, Jaguar used EP80 when they built AJ6 engines.
I'd fit an oil pressure gauge to make sure you are making pressure - even if you just use it to check the engine function rather than install in the car.
Follow this and you should be OK.
Do not underestimate the need to lap the crank, it removes the microscopic saw teeth that will chew the bearing up, and remember it is crank direction dependent. Consult your machine shop if you have questions.
I would use a countersink on the oil holes then a half round file to make sure that there's no chance of the oil hole picking up the bearing, and use a long twist drill to clean out all of the swarf that will have collected in the crank during grinding. Blowing out simply won't cut it, unfortunately.
You also need to clean out all the block galleries in a similar way.
Once the bearing is ground I would use plastigauge to check the bearing clearances.
Use very thick oil to build the engine, Jaguar used EP80 when they built AJ6 engines.
I'd fit an oil pressure gauge to make sure you are making pressure - even if you just use it to check the engine function rather than install in the car.
Follow this and you should be OK.
Id be looking at the engine building/blueprinting/spec sheet for it and checking the tolerances made sense first off.
Seems odd that the builder "says its ok".
Id have thought youd have a spec sheet with all the relevant measurements and checks in written form for you to confirm?
Oil starvation deffo sounds like the issue here.
Have you had the pickup strainer checked?
If its blocked with previous debris it could create this fault, as could one thats cracked and allowing air in.
Seems odd that the builder "says its ok".
Id have thought youd have a spec sheet with all the relevant measurements and checks in written form for you to confirm?
Oil starvation deffo sounds like the issue here.
Have you had the pickup strainer checked?
If its blocked with previous debris it could create this fault, as could one thats cracked and allowing air in.
If it keeps doing the same thing on one big end pin with a different crank and rod then I'd be looking at things that could be different in the block on that cylinder. Is the bore correctly centred over the crank pin and bored vertical? Check the main bearing clearances on the main or mains that feed that big end. Maybe the block needs line boring.
Is the compression ratio or the piston to head clearance wrong on that one cylinder? I've seen engines built with the pistons hitting the head at high rpm because the block had been skimmed too much. Is there any evidence of detonation on that piston? Something must be mechanically amiss, it just needs finding.
Is the compression ratio or the piston to head clearance wrong on that one cylinder? I've seen engines built with the pistons hitting the head at high rpm because the block had been skimmed too much. Is there any evidence of detonation on that piston? Something must be mechanically amiss, it just needs finding.
Edited by Daveuk9xx on Tuesday 17th June 11:40
marT350T said:
The engine builder did say that there evidence of detonation one one psiton. Dont know which one though.
Please could you explain why/what effect this would have on the bottom end.
Cheers
Detonation is uncontrolled combustion, causing a pressure spike at an engine position that causes the piston/rod assembly to push down on the bearing/crank, pushing out the oil film between the rod/bearing/crank, increasing wear.Please could you explain why/what effect this would have on the bottom end.
Cheers
Edited by Marf on Tuesday 17th June 12:57
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