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Triumph TR6 - Engine Bearing clearance?

To you engine experts,
I wish to confirm the clearnace spec on both the mains and rods bearings 1971.
I have the following information that I quote:

"The connecting rod clearance should be 0.0086-0.0125". If you are within spec, remove the Plasti-gage, reapply fresh assembly lubricant, and refit the bearing cap, torqueing to 38-46 lbft. " Sounds like a lot or is this because of the plasti-gauge? Can not say I have used plasti-gauge before:)

"Proper clearances are another factor that are extremely important bearing longevity and oil pressure. Crankshaft bearings generally need at least a .0001 inch thick oil film between themselves and their journals to prevent metal-to-metal contact. This requires assembly clearances that are loose enough so oil can flow into the gap between the bearing and journal to form an oil wedge that can support the crankshaft. The clearance must also be sufficient to allow enough oil flow to cool the bearings. But the clearance must not be too great otherwise the oil will escape before it can form a supporting wedge.
Excessive bearing clearances (more than about .001 inch per inch of diameter of the crankshaft journal) can allow a drop in oil pressure...."

And finally: "One large production engine rebuilder says they try to build all their passenger car and light truck engines with about .001 to .002 inch clearance in the main and rod bearings. This compares to as much as .004 inch of clearance that may have been present in the OEM engine. But on some engines, such as the General Motors 173, more than .0015 inch of clearance can result in noise "

There is a discrepancy in the amount of clearance as said above.

I looked in the shop manual and could not find either spec.
I have bought .010" oversize bearings for both rod and main.
Any recommendations appreciated.
Thanks
Rick C
Rick Crawford

Rick, I have always thought clearances on the main bearings were in the 1.5 thou range, .0015", I don't remember where this info came from, in my memory it has now reached the status of something I "know" and don't question; which does NOT mean it is correct.
I have seen a Plastigage used, very clever, should be accurate.
As I drive a 4 banger my workshop manual will not necessarily give the correct info for your "6", praps someone can confirm.
Hate to get it wrong on something rather critical, good luck!
Simon.
Simon

Simon
Thanks.
But you race your 4 banger so you put it through its paces a little more than I will my 6:)
Just dropped the crank off and he said around 1 thou for both. He commented on the plasti-gauge saying it is most often used incorrectly. He said most people only put one strip in and of course the crank weight adds to the compression of the gauge. He said the proper way is to use 2 pieces top and bottom of the crank on both bearing surfaces. Funny the shop manual does not say this.
Rick C
Rick Crawford


Rick,

You might be dissapointed if you think you are going to get tighter clearances than .002. I did alot of research on this and found triumph engine builders allowing up to .003" for both mains and rods. The engine shop that did my engine (they build race engines) tell me .003" is quite common. Only newer tight spec engines run in the .001 range. Many racing engines run at .004 to .005 so they can run alot of oil through them. This is course all of what the engine people tell me. The enging shop measured my clearances at around .0027". They said it's fine.

By the way. My Bently manual spec's it at .0027 when using plastigage
HP Henry Patterson

The .0086" and .0125" are the side clearances for the rod, not the bearing clearances. When checked with Plastigage, the bearing clearance should be .001" to .003" (or as stated above, .0027"). As for the crank side clearance, that is what the thrust washer thing is all about.
SteveP

This thread was discussed on 18/03/2005

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