Small end bushing

[Sjors]

Hello all,

I can only find the wear limit for the smaller type piston pin bushing, not the 34,9 mm one.

The new piston pins are 34,92 to 34,93 mm. The bushings bores are about 34,95-34,96 mm with exception of the bushing where the cracked piston pin was discovered. This bushing has a high read of 34,98 on one side.

What is the range of allowable tolerances?

Thanks! Sjors

[Billy26F5]

I see what you say, I would apply the same clearances, so all small ends should be ok as long as the conrods themselves are ok except the damaged one which exceeds the recommended max 0.0018" clearance (at this stage I would put in new ones all round if you have new pins). If you replace a small end bush you'll need special tools as they're unfinished and need to be reamed to size on a special reamer with a pilot fixing for the big end to ensure they're accurately parallel.
Sandy

[LakeLox]

Had to replace two rods in my rebuild recently, bought a full rebuild kit and just resigned myself to the fact I wasn't building a F1 Engine and couldn't justify too much more expenditure with sending parts away to be finished like the small end bushes given I live out in the bush and there are no machine shops nearby. I bought an adjustable 35mm reamer and just did them myself. Make sure you use the reamer dry on the bushings with no lubrication at all. Had a local old-timer engineer tell me to burnish the bushes by turning the reamer backwards to finish the bearings off. Not sure where I found the info but the test was to lubricate the wrist pin and let it fall though the little end under its own weight!!, took a bit of doing but it all measured up okayed within specs I used. Anyway to seems to have worked out ok, the engine is running fine. I also found the sizings for the larger pins in my manual here is Australia in the linked pics. Cheers

https://postimg.cc/gallery/1ZJjPqxm

[Billy26F5]

Very interesting, I like this kind of thing, how did you set up the reamer to get it parallel to the big end? I think the I&T manual got this from the Ford manual at some stage, but it's good to know that it's there. Very good looking finish, the fact that it's running fine is always a good thing.
Sandy

[LakeLox]

I looked into making some sort of jig but after speaking to a few people just decided to calibrate my eye to about ten thou, and let it rip from there. Like I said, it was not a F1 Engine and I figure the way it was running before I got to it, anything I did was going to be a marked improvement. I guess only time will tell, I've seen some very rough jobs go together over the years and still seem to be running well today.

[Sjors]

Hello,
thank you for the post with the tolerances for the 35 mm eye.
Yesterday evening I was busy with my rods. I measured the eyes with a special dial indicator for holes (cilindercontrolleur in dutch language) which I could borrow from my employer. The eyes varied between 34,935 and 34,35. I suspected one cilinder from a waterlock in the past and the eye of that rod had 34,98 on one side of the bushing. So I suspected the red to be bent. But how to measure that without a profession jig like the pics in the manual.... Fist I pressed the old bushing out of the rod eye.
I found a pretty accurate way to measure if the the bores of the rods are parallel: I clamped a large vernier caliper vertical in the vice (soft jaws of course) with the fixed end of the caliper in the jaw (but the fixed end sticking out horizontally) vertically pointing the ceiling. You know the jaws of the caliper are perfectly parallel (luck this is a new vernier caliper without play or wear). I took the rod vertically and slide the bores over the jaws of the caliper and let the big end bore rest on the fixed jaw of the caliper by gravity. Then I slide the movable jaw of the caliper (which is sticking in the small end of the rod) downward against the small end bore (without bushing). Check and sure the big end is sitting flat on the fixed jaw. Then look how the movable jaw coming down against the small end bore. These surfaces should mate without a gap on one side.
My rod had a small gap. This was further confirmed when I layed a straight edge on the stern face of the small end and the straight edge pointing tot the big end. I decided to try to correct the slight bent with the shop press. This is not allowed by the book but I take the gamble. The rod is pretty flexible and strong so it needed just above 4 US tons a few times to do the correction.
After that I pressed the new bushing in. Still have to make the bore fitting the new pin.

[Billy26F5]

Bent conrods can bite back, but hopefully if the small end bush is finished parallel you should be ok if there are no excessive stresses. I like the use of the calliper to check this. That's quite a difference in sizes, but hopefully the new ones will be ok. Best of luck with the reaming.
Sandy

[Sjors]

I decided to renew all bushings, not only the one. Otherwise I'm going to have one nice and tight bushing and 5 more or less sloppy ones
Don't want to save on the wrong end, otherwise I'm convinced that the engine will not fale on these bushings before someting else is worn.

[Billy26F5]

I think that's the best way at this stage. Super Billy has new ones too.
Sandy

[LakeLox]

While you're there you might as well do what you can and what you can afford. The last thing you need is to be back again anytime soon