Balance drillings/ crank strength

Hi all,

This is from a 2.8 litre crank. It was ground undersize and it has these balance drillings. Jaguar balanced them with a grinding wheel so these have probably been done later.

I don’t like the holes. Especially not in that location. Do you think that is okay to run or is this a weak spot? In other words, is that done commonly?

Thanks, David

It does seem an odd position due to being close to the crank C/L
Being the 2.8 crank the throw is less than the bigger engines so if you keep the revs reasonable I don’t think there would be any problems.


I will second the odd location assessment. Why there? Especially since it looks like they had to first grind a flat spot to drill. It been a reeaaally long time since I had to calculate such things, but my recollection is that the amount of weight removed or added is proportional to the square of the radius from the principal axis of rotation. That is, if it took one ounce to achieve dynamic balance at radius R, then it would only require 1/4 oz at 2R.

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I also thought it was an odd location to drill. And it just had to be on the last crank throw before the flywheel! I don’t have a real use for the 2.8 but someone will need something some day and it’s a neat little XK. Maybe I do get it to run, but it also had an odd timing chain problem where the chain ate through all the guides and more.

So if there’s no acute concern about the drillings being a stress riser I will leave it as is and live with it. The rods and pistons are much lighter too… it‘ll live.

Thank you both, that eased my mind!

Add me as a third: on a streeter, I’d not worry about them.

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If I ever get it to run… will I really stop at 6000? :grimacing:

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Probably not, and then you’ll find out how strong that crank it is!

It’s pretty cute. I‘ll take a comparison picture vs. the 4.2 some time. The 2.8 crank is actually easy to carry…