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TR2 Engine rebuild

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Possible question for Mick Richards, I am part way into an engine rebuild, reground crank, new pistons, liners bearings etc. Has any one an idea as to the acceptable

torque required to turn the crank over. At present it takes approx 44 - 46 lbs ft. At this figure it just seems a bit tight when the pistons are at the top or bottom of the cylinders. 

Bob E 

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Hi Bob

there are many parameters that could influence this.

How was the crank rotation with no pistons etc? With just the main bearings torqued ?

Did this change as you put each piston into the equation?
Bearing caps, mains and big ends,  can sometimes be out of true and pinch a new bearing, so try torquing one at a time to eliminate any issues.
Are the piston ring gaps correct? 
Is the cam shaft in and the front bearing dragging on the rear of the chain wheel? Wrong clearance here can seize everything up.

Just  a few initial thoughts


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Thanks Ian

In reply to your questions :-

Crank rotation with no pistons fitted was OK, with each piston fitted it gradually became tighter but this is what I would have expected, piston rings gaps are OK. The camshaft is not yet fitted I will try releasing the all of the present torque settings tomorrow and try again as suggested.


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Hi Bob,

Well Ian has many of the correct questions outlined and turning torque is a variable which depending upon piston dia (bigger is more drag because of increased ring circumference area o even varying ring material) and what clearances you are running on piston to liner. Road use at standard 3 1/2 thou piston to liner or race use where you could be running anything up to 5 thou depending upon piston material etc. All these variables change the turning torque, and so the torque should be established from the very first crank fitment and the engine built in a modular fashion where you can establish the increase in engine "stiffness" as the equipment is added. 

As Ian intimates turning torques should be established from the very first crank fitment, where the crank is fitted with front and rear main bearings only and then measured (checking crank for straightness by DTI) and then the front and rear mains variably taken off and compared against the centre main to establish whether any out of straightness is between front and rear main bearings or between the centre main and the nose main. Suffice to say with bearings set at race clearances with crank fitted only I expect the crank to be turned by the nose by finger use only (it should spin by flicking the fingers) which equates to less than 1 lb ft torque. As you add the various components, correctly gapped piston rings (I use at least 15 thou on compression and about 20 thou on the second ring (I'm not anal, it makes bugger all difference) and yes I space the gaps including any on the oil rings also even though I know within 100 miles they'll be all over the place (it just makes me feel better). You are looking for incremental torque increases for individual multiple piece components, ie fitted to freshly oiled bores No 1 piston in place an increase of 4 lbs ft, combined with No2 piston in place an increase to 8lbs ft etc which makes any non complying item stand out if the torque rises exponentially. That then requires a strip and investigation to find out the problem.

It's quite common to notice the increase in torque required as a pistons reach the end of their strokes, the reversal of rotation has to flex the piston rings in their grooves and causes an momentary stiction (sticking friction|) which you will pick up, as long as the engine turns freely through the midsection where pistons are neither at top or bottom. You are still at a stage where the pistons can be removed easily and torque established for the crank alone and then the component additional torque noted as individual pistons added.   

Mick Richards

Edited by Motorsport Mickey
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Thanks for the very informative reply Mick, just for further information I am fitting the 87mm piston/liners set. So it looks like a strip down and restart all over again. Just one of the joys rebuilding a TR2, at least it helps to  passes lock down time???? 


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