Engine builders, I need HELP!!!!

[2003z]

I don't know if its the way I am measuring, if I got the wrong rings sent to me or what!

To start:

F54 block / P90 head, standard dished pistons. The engine ran fine, no blow by or excessive oil consumption, just lower compression than I wanted.

I am upgrading to Nissan Motorsports cast pistons, in stock bore. I had the block hot tanked and honed.

I measure the bores at 3.386 inches, 86.01mm which is in spec according to the clymer manual, but when I slide a ring into the cylinder to check the end gap, it comes out to about 4mm instead of the .2 to .4mm it should be.

I don't know what to do at this point. I thought the machine shop took too much material off when honing, so first I bought a set of used oversized pistons from Dannys Datsuns and was going to bring the block back to get it bored, but they wound up being L24 oversized pistons when they arrived, so that was a waste of $150.

I thought maybe I got rings for an L24 instead of an L28, but the rings I have are larger than the L24 rings that came on the above pistons.

I just got another block from a friend, but its actually been overbored already, as its got 87mm bores.

a couple of pictures

I didn't use this caliper to measure the bores, I used a dial gage, this is just for illustration and is not accurate.

[Ed]

The ring end gap for the top comression ring is 0.005 in. for each inch of bore. 0.004 for the second comression ring.

If you have 3.386 of bore X 0.005 = 0.0169 in. for your top ring end gap.

We must assume that the bores are round and have little or no taper. A bore with 0.001 taper will give about 0.003 variation in the end gap as the piston moves up and down the cylinder.

[Phred]

Mike,

You just have the wrong rings. If you have a 4mm ring gap on a stock bore, thats all it can be. BTW, most blocks are closer to 3.390. Don't worry about the machinist removing too much with the hone, it should only take a few thou to clean up most blocks, as they generally don't wear that much. Ring gaps change at the same rate as Pi. For each .001 in. the bore increases, the ring gap will increase 3.1416. Ed has good data, and will always be a safe rule to follow. In real life, rings on L NA motors can be safely set a little closer. Even SCCA ITS engines show no ring butting with a lean mixture at .015 on the top ring. Hope you find the right rings for that tractor motor.

Phred

[2003z]

yes, it turns out the rings were the wrong size. I got new ones and everything is going together fine now.

Thanks!