SILV-O-LITE 8-1017 Piston Info?
 

Howdy,

I have a barn find 1941 Mercury block in the machine shop and after a parts wash, it looks like it was freshly bored, covered in grease, and stuck in the corner to collect dust for decades. It was originally 3.1875, but is now 3.280.. which is roughly 3/32 or 0.090 over. The bore is so beautiful that I would like to just run it as-is... except I'm not finding any pistons online in that oversize. Seems like 3.3125 opens up a plethora of choices.

I didn't get any original engine internals with the barn find except the old (floater style) crank. I was just looking back through the boxes of random parts (mostly Model T stuff) and discovered a box of NOS Silv-O-Lite 8-1017 pistons marked 0.090 oversize. Cool!

The pistons measure:
3.255 across the top of the piston
3.265 on the skirt just under the wrist pin
3.275 on the skirt 90deg to the wrist pin.

Hmm.. that final number is 0.005 under the bore, 3.280. Maybe these are in fact relevant to my project.. I'd definitely accept thoughts on that fit from the experts.

Since I don't have rods/bearings, and only have a rough old crank that needs attention anyway, I was thinking of just dropping in a 4" crank while it's all apart. If the pistons won't work with a 4", then it looks like I'll be refurbishing my old crank and finding some floater rods/bearings. Anyone have some for sale?

My pursuit for Silv-O-Lite 8-1017 information continues. They're not showing up in modern catalogs. Basically, I just want to see if these are suited for this application.. and even better, if they can be used with a 4" crank. Thanks for any help.

Re: SILV-O-LITE 8-1017 Piston Info?
 

A .005 inch clearance would be more suited for forged aluminum pistons. Cast aluminum pistons should be closer to .0025" to .003" clearance for best longevity. This is why most folks bore the cylinders close but just under minimum clearance for piston skirt size then power hone the bores to the correct fit. The pistons should be in hand prior to any boring or sizing.

The .005" clearance may work OK for a while but the engine may end up with premature piston slap. This could be problematic if the bores need further honing due to light corrosion or something of that nature.

United Engine and Machine Co is still around. Here is a link:
https://uempistons.com/

Re: SILV-O-LITE 8-1017 Piston Info?
 

Yeah, I was excited to find numbers so close, but not as excited that they were about double what I was expecting.

I called UEM and they didn't have records back far enough to find my pistons.

Re: SILV-O-LITE 8-1017 Piston Info?
 

You need to measure the diameter 90 deg from the pin and just above the bottom of the skirt.

Re: SILV-O-LITE 8-1017 Piston Info?
 

...and you could have piston skirts coated to compensate for too much play. Have done this on several motorcycle engines from big bore blown Alky Vincents to high revving two stroke CZ and Yamaha bikes.

Re: SILV-O-LITE 8-1017 Piston Info?
 

3.275".

Re: SILV-O-LITE 8-1017 Piston Info?
 

Probably need to go to .100 over pistons. Then you could order them for a 4" stroke.

Re: SILV-O-LITE 8-1017 Piston Info?
 

Yeah, I'm thinking I'll have to bore it to a more standard and available size.

I talked to Ross and they said .100 over would have to be custom. I looked at Egge and their L-991 do come in.100 over and 4" stroke. Seems like a winner so far.

It's a shame that this block appears to have been prepared for these pistons, but that gap is just a bit too much for me to comfortably run with it.

Re: SILV-O-LITE 8-1017 Piston Info?
 

Just making sure, you are measuring with cylinder and piston mics, correct?

Re: SILV-O-LITE 8-1017 Piston Info?
 

Be interesting to know if those pistons are for a 4-in crank, or 3.75 crank (or something else). I didn't see it mentioned. A quick look-see measurement should tell.

edit... oops... I see this has been addressed on the hamb...

Re: SILV-O-LITE 8-1017 Piston Info?
 

You could get the pistons Knurled If you could find someone wiyh aan old Perfect circle machine, but then you'll need rings. Bent gp with the .100 over or 125 which would be a 276 with the 4" crank.
Gramps
I had one of those piston nurlers