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Discussion Starter · #1 ·
Hi. I'm working on a '67 Triumph TR6 650 engine. For the connecting rod big end journal to bearing clearance the manual states a range of .0005" to .002" as the acceptable clearance range. I have new bearings installed. The crank and rods have been sitting in my cool-to-cold garage. With plastigage I'm getting a clearance measurement of .002" on both left and right. I've read that bringing the parts up to room temp can have a positive affect on clearances (making them tighter). It my not be noticeable but I'll measure again tomorrow night once the parts are warmer (I brought them inside this evening). What do you think about this .002" measurement and it being at the 'loosest' end of Triumph's range? I wonder if this range is the range within which a Triumph engine can be built, and if wear causing clearances larger than .002" is planned and acceptable?

What do you think?
 

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what does your crank journal measure? the min and max is listed in the manual, it may be time to have it turned down and get oversize rod bearings.
 

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Discussion Starter · #3 ·
what does your crank journal measure? the min and max is listed in the manual, it may be time to have it turned down and get oversize rod bearings.
I measured them a couple months ago but didn't write down the numbers. I'm pretty sure I checked my measurements against the manual specs and I'm pretty sure the numbers were within spec. I'll measure again tomorrow and post the numbers here.

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Discussion Starter · #4 ·
Something I calculated last night is that the range between .0005" to .002" is only .0015". That is fifteen ten-thousandths of an inch. Not much of a window to adjust within.
 

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You're being too fussy;these things are built like lawnmowers with an oil pump...if the plastigage is saying 0.002" you're fine. Lube it up, put it together and ride it.
 

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Discussion Starter · #7 ·
Hi. I'm working on a '67 Triumph TR6 650 engine. For the connecting rod big end journal to bearing clearance the manual states a range of .0005" to .002" as the acceptable clearance range. I have new bearings installed. The crank and rods have been sitting in my cool-to-cold garage. With plastigage I'm getting a clearance measurement of .002" on both left and right. I've read that bringing the parts up to room temp can have a positive affect on clearances (making them tighter). It my not be noticeable but I'll measure again tomorrow night once the parts are warmer (I brought them inside this evening). What do you think about this .002" measurement and it being at the 'loosest' end of Triumph's range? I wonder if this range is the range within which a Triumph engine can be built, and if wear causing clearances larger than .002" is planned and acceptable?

What do you think?
So I brought the crank and rods indoors last night. They were in my garage for weeks and the high temp in the there was around 50. I rechecked the clearances tonight with the parts up to room temp and the parts definitely flattened a hair wider of a patch of plastigage. Before the clearance was right at .002". Now the clearance is just a hair tighter. Interesting, but I'm still curious about being on or near the maximum side of the specified range. I'm wondering if the manual's specified range is a 'build' range, meaning if you are one either side of the range or within the range then you can run the engine for 20k miles or more.
 

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Maybe try another set of bearings?

Are the ones you have OEM or do they come from 'elsewhere.'
 
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