Howdy, I have a barn find 41 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 over. The bore is so beautiful that I would like to just run it as-is... except I'm not finding any pistons in that oversize. I was looking through the boxes of extra and random parts that I got out of that barn and discovered a box of NOS Silv-O-Lite 8-1017 pistons marked 0.090 oversize (pretty close to 3/32). Cool! Except... they're measuring at 3.255, so whatever they were for is not my engine. Maybe it was a coincidence, maybe a misunderstanding decades ago, I do not know. Nor can I find any info about these pistons, either from the current Silv-O-Lite catalog or the Google machine. Anyone know what they're from? Furthermore, anyone know where to find 0.090 oversize pistons for a 4" stroke flathead? Or, do I need to punch out these beautiful bores another 0.030 to get to 3.3125 and the wide variety of pistons at that size?
The measurement I quoted above was across the top of the piston. I also measured the skirt and it was something like 0.010 larger. I'll have to verify when I get back home.
Is the bore cross hatched finished? If not I wonder if it was a preliminary cut for some sleeves? Seems the engine project stalled, so has me wondering
Measure 90 degrees to the wrist pin, the crown is the smallest part of the piston. What are you using for measuring tools? Sent from my iPhone using H.A.M.B.
yup, use a 4" micrometer, measure half way down the skirt, perpendicular to the pin bore. the diameter of the ring lands won't tell you much about the bore size the pistons will fit.
Pistons measure: 3.255 across the top of the piston (I should have known better). 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. 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.
what is the pin height? Center of pin, to top of piston (preferably at the edge of the piston, which would be about even with the top of the block). should be around 1.43" I think if they're for a 4" stroke As for the skirt size, vs bore size...if you use a micrometer and a dial bore gauge, you can find the skirt clearance. Most folks don't have this equipment.
With the latest measurements given that 0.005 might shrink a bit more with the right tools. I recall running some pretty loose numbers waaay back when. Now the 4" issue.
0.005” is so close, I would certainly make sure measurements are accurate. As squirrel said the proper tools are key here. I measure each piston then set my dial bore gauge to that number and measure the bore, that gives me the difference or the piston to cylinder clearance. Measure the bore in four places to check for taper and out of round. Two at the top and two at the bottom. Sent from my iPhone using H.A.M.B.
There's a chamfer on the edge of the piston.. so measuring from the top edge of the chamfer (before the dome) to wrist pin center is right about 1.550. I'm going to supply the machine shop with these pistons, so measurements aren't lost in communication. In my research, I've read a little about the Silv-O-Lite 1058s, which are the current Ford/Mercury flathead offering.. and that's all they offer for 1939-1953. I was hoping to reverse engineer my 1017s from 1058 dimensions. They callout the 1058 stroke as "stock." Well, we know Mercury came out with 4" stock stroke, so.. it would be nice if they provided an actual number. I can assume they mean 3-3/4", but I don't like assuming. I even called them directly and the guy was nice enough but basically could only regurgitate the same exact info from the catalog and said 1058s are for a "stock" 1939-1953 Ford/Mercury stroke. Okeydokey.. I asked if he had any info on 1017s and he said his catalog goes WAY BACK, so probably. After a brief hold, he came back and said mine must be really old because his catalog goes all the way to 2012 and mine aren't in there. Yeah, we're probably needing another 50 years beyond that.
If the gap double- checks at 0.005 at the machine shop, I'll have to punch it up to 0.100 over. That would be a shame, but I don't want to damage an engine that I'm putting good money into just because I had some mystery pistons on the shelf. Looks like Egge L991, .100 over, might be the ticket. I'm seeing conflicting results about whether they hit the head, so I'll have to research that further. I have a set of Offys that I'll be running. Edit: Called Mike at H&H and he said the Egges are good to run and have been for a while now.
Just a guess - if the pistons you have were found with the block and not much else - most likely why it stalled and got put to the side.
That's what I'm thinking, too. I don't have any history on this block, and most of the parts that came in the pile are unrelated Model T stuff, so I hadn't given this much thought until the bores shined bright when the grease and dust was washed off. Maybe the previous owner had the block bored for these pistons and the machinist goofed with too much clearance and the project stalled to sit in the corner until decades later when I came along to save it. I will drop the pistons off at the machine shop tomorrow so he can take a look, but I'm already mentally prepared to buy some 0.100 over EGGE L991s.
My guess is those underwear are older than the guy at silv-o-lite. Sent from my iPhone using H.A.M.B.
Do you know if these pistons are cast or forged? On some later style engines with forged pistons it's not unusual for them to have an extra couple thousandths of clearance cold. At operating temperatures they expand enough to bring down the clearance and run quietly. But I have very little flathead experience and even less knowledge of Silv-O-Lite pistons. To accurately check piston to cylinder clearance you might want to pick up or maybe borrow an assortment of ribbon gauges. They're like a longer (6" to 12") version of the feeler gauges you'd use for setting ignition points or valve lash. https://www.mscdirect.com/product/details/01479062 https://www.mscdirect.com/product/details/06198022 https://www.mscdirect.com/product/details/06588321?fromRR=Y
Just for fun I looked up Silv-O-Lite's address from that early label. It's now suburbia, but the Automotive Industries magazine of June 1st 1952 shows Silv-O-Lite still at that Preda street address. Someone on here must have an early Silv-O-Lite catalog that could be checked for the mystery part number.
The Jalopy Journal
