Spitfire bottom end advice

J

jbecker

Well-known member
I seem to be be experiencing excessive rod bearing wear on #2 and #3 rods in my 1296 LP Spitfire motor. Any advice on block or crank modifications that might increase short life span of the bearings. Running 10.8 compression and 7500 rpm. Seams bearings should last longer than 3 hours. Running 11:1 compression and 7500 rpm my LP Mini bottom ends lasted several seasons.
Any ideas or suggestions would be appreciated.
 
Never more than .020” undersized journals. Check clearance never more than .002. My 1500 lasted 3 years at 7000 so something is definitely wrong. Make sure it’s balanced correctly and check that the side clearance is within spec (can’t remember off hand).
 
What oil? What oil pressure/temperature? What oil pan?

Is the #2 main grooved? What is main clearance? Is the crank just a straight drilling from main to rod or are there cross drillings? If straight through is stock, do people often add a cross drilling?

Is this a large or small main crank?

I've forgotten all of the details on the Spitfire beyond the fact (IIRC) that the 1300 had large and small main cranks and that (IIRC) the small main was preferred, but I suffered through rod bearing failures in my old 3 main bearing Datsun 1600 Roadster and had to make several changes to get things happy.
 
In answer to questions:
crank is 10/10
Bottom end balanced by experienced machine shop that has built numerous successful race motors and balanced my mini cranks
Valvoline ZR1 50 weight racing oil. Steady 60 psi on straights and in corners. (review of video verifies no drop in pressure in corners)
Pan is modified to prevent surge during cornering
Crank is not cross drilled either on mains or rods. No grooves machined in main journals.

Thanks
 
jbecker":17h7phnm said:
In answer to questions:
crank is 10/10
Bottom end balanced by experienced machine shop that has built numerous successful race motors and balanced my mini cranks
Valvoline ZR1 50 weight racing oil. Steady 60 psi on straights and in corners. (review of video verifies no drop in pressure in corners)
Pan is modified to prevent surge during cornering
Crank is not cross drilled either on mains or rods. No grooves machined in main journals.

Thanks
Click to expand...

I was asking about grooves in the center main bearing shells, top and bottom.
 
Bearing shells are grooved.
Bearing clearance .002 to .003
Number 1 and 4 bearings are fine.
Is there a way to supply more oil to the center main and hence the 2 and 3 rods?
I am using the best bearings I can find. Vandervell rods are really hard to find but I have 3 sets of Vandervell mains
 
As Aaron mentioned the center main oil feed can be drilled to 5/16 from the bearing saddle up to where the passage turns towards the driver's side oil galley. If you remove the oil pump shaft guide insert (drive it up and out of the block) you can drill though the oil pressure sender hole, past the galley and to intersect the passage up from the center bearing. This is mentioned in the Triumph race prep manuals for the large crank motors only. No need to do this on the front and rear mains. If you do this make sure the oil pump spins freely after pressing out and reinstalling that insert.

The Vanderville main bearings have a larger circular oil grove than the otherwise good King tri-metal bearings. I would use Vanderville main bearings on the centers and easier to find Kings on the front and rear main.

I have seen older Moldex prepped Spitfire cranks that have rifle drilling from the #1 rod oil passage to intersect with the #2 rod oil outlet and likewise on the rear. That way the middle rods can get oil from center main and less directly from the front and rear main. I am not sure how well oil flows in a W pattern on a spinning crank but any more oil to the #2 and #3 rods has to be a good thing. More conventional cross drilling the #2 and 3 rod bearing portion of the crank for 2 oil outlets one on each side is considered a good fix. This requires more drilling than it sounds to line up the new holes with the feed passage but it is an established way to modify a crank for more oil flow.

The large cranks seem to have a resonance over 7000 RPM that adds to wear. I suspect the inconsistent oil clearances when the center flexes adds to oil delivery problems. ATi had a balancer blueprint on file they can make for the large crank which should help with when resonance occurs. Also a very good heat treating of the crank should help some on this issue.

There are some other things out there that have been tried but since there are fewer people racing Spitfires some of the info seems to fade away. Good luck - Tom
 
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