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TT1, 749R, 900M, 944ssie, 500 Pantah, 900GTS
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Discussion Starter #1
I’d be interested in considered & serious opinions regarding the cause of this:


990592

990594

990595

This carnage occurred after approximately one hour of running following the complete engine overhaul of an 1100ds. Crank had been ground to 41.5mm & EVR shells fitted. Plasti- gauged to .002”. Engine had immaculately clean & oil pressure correct.
 

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yeah, oil or crank surface would be the most obvious. does suck. nothing worse than having to pull a fresh one and finding shit like that.
 

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Hi 33
Are the rods journals aligned? Centre of crank pin has pick up on one side and not the other.
The anti rotation tabs on the bearing shells look damaged, what do the outside of the shells look like?
Have they spun?
I see you have plastigauge clearance.
Did you check crush? What was it?
What do inside of big ends of the rods look like?
 

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To me it looks like lack of lubrication, oil pressure at the test point does not guarantee it's getting to the bearings. In fact if the crank was blocked it would have better oil pressure as there is less places for it to leak out.
 

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Discussion Starter #7
Hi 33
Are the rods journals aligned? Centre of crank pin has pick up on one side and not the other.
The anti rotation tabs on the bearing shells look damaged, what do the outside of the shells look like?
Have they spun?
I see you have plastigauge clearance.
Did you check crush? What was it?
What do inside of big ends of the rods look like?
Hi. Good questions:
The assymetric wear in the centre of the crankpin is due to the bearings having crush/spread under load as they were hammered.
One set had started to spin in the rod as the clearance opened up - taking the location tabs out as you’ve observed.
The plastigauge clearance was 0.002”.
The rods were perfect.
The oil was high quality & pressure & delivery are not suspect - also supported by the fact that the big ends had not seized!

Other info:
The pin was ground to size elsewhere & I’m not convinced that it was hardened during that reclamation.
The bearing shells are from EVR in Italy. 0.25mm undersize. However, I suspect that they are OE bearings, to which additional plating/coating has been applied in order to resize them.
 

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What was the reason for the rebuild?
Did you check bigend crush when platigauging?
Is there enough of the crankpin without pickup/ fretting to measure and check that it was ground round and parallel?
What assembly lube are you using?
 

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Discussion Starter #9
The engine had been built elsewhere after being ‘vapour’ blasted. The big end had picked up on blasting media causing scoring, hence the regrind.
Confess that I didn’t measure crush, but fail to see how this would be of any great concern given the rod eye being round & std (as were the base shells) Etc.
Given that the rods & shells were supplied to the crank grinder, one would it to be dimensionally correct. Maybe I’ve a lesson to learn here?
Lucas assy lube.
Don’t think there’s enough untouched crankpin left to measure.
 

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You have my deepest sympathies. 😢
 

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It's interesting that you note that the cases were vapor blasted. I am not saying that a similar instance occurred here, however a friend had an R90S engine completely apart and the cases vapor blasted. Then these were cleaned in hot water and then solvent. A short time after reassembly, the crank failed in similar fashion to yours due to grit that was not extricated from the cases prior to reassembly. The prognosis was that that grit was embedded in the aluminum that was released under heat and trashed the crank.
 

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toyota 4age bearings fit, you just need to cut another locating groove in the rods to have them centred. acl do a race series and they come in lots of undersize and cheap. not sure if there's enough left there or not though.

i've been told the sulphur nitriding isn't really needed, but i'd do it out of superstitious paranoia.
 

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Discussion Starter #13
toyota 4age bearings fit, you just need to cut another locating groove in the rods to have them centred. acl do a race series and they come in lots of undersize and cheap. not sure if there's enough left there or not though.

i've been told the sulphur nitriding isn't really needed, but i'd do it out of superstitious paranoia.
Thanks for the heads up re. the Toyota bearings.
 
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