3 3/8 Too big? I know it's been discussed before
 

It's potentionally a street motor. Is a 4 ring piston going to wear less/better than a three ring?
What are the pros and cons?
I also could drop a mere crank in. I have a 59a and an 8ba to choose from for a build

Re: 3 3/8 Too big? I know it's been discussed before
 

The best engine size Have experience with is 5/16 x 1/4 ran super strong and lasted 36fordguy

Re: 3 3/8 Too big? I know it's been discussed before
 

You'll probably get a bigger power increase from modern 3-ring pistons using the thin new Moly rings than by the overbore from 3 5/16" to 3 3/8". 4-ring pistons are old school with increased friction and not needed with modern ring design and oil.

If you already have the 4-ring pistons, leave the fourth ring off and have the assembly rebalanced. I've done it and it works.

Re: 3 3/8 Too big? I know it's been discussed before
 

Given that it is getting harder and harder to find good blocks and the fact that many have lost some of their bore thickness due to rust, I won't bore them to 3 3/8 anymore.

The bore that I use the most (if I'm chasing street cubic inches) is 3 5/16 - with whatever stroke you want to run and have parts for. With a 4" Merc crank this gives you 276 cubic inches - which makes a really nice street engine that can usually take 2 - 3 more over bores before the cylinder walls are too thin.

Before you bore the block, it should be magged, pressure tested and sonic tested - so you know what you have to work with. Knowing the cylinder wall thickness before selecting a piston/bore size is the smart way to do it. It can definitely influence your final bore size goals.

I'd run 3 ring pistons - there is no reason to go to 4 ring pistons (just adds friction for no gain). There are a variety of manufacturers - depending on whether you want to run cast pistons or forged ones. I prefer to run Ross forged pistons with a metric ring pack as I like the chrome moly rings and the less friction the better.

Re: 3 3/8 Too big? I know it's been discussed before
 

I have 2 blocks that are already 3 3/8. I just want to get them running. I appreciate your feedback. I got a load of parts from a guy here in Ct that passed away I got some smaller bore blocks as well I’m learning how to measure bores and cranks. I have a set of Elgin 3 ring racing pistons on 21a rods ready to go. I’m going to take a shot at setting up some floater bearings on an eagle 4 1/8 crank. Does anyone have any advice lol?

Re: 3 3/8 Too big? I know it's been discussed before
 

How do I order rings? They are 3 3/8x3/16LC with 3/32x3/32x5/32. Boredandstroked I enjoy ready your posts. Thanks

Re: 3 3/8 Too big? I know it's been discussed before
 

I was thinking that the 4 ring would stay straight in the bore better but I’m happy to use the 3 ring
Thanks for your advice

Re: 3 3/8 Too big? I know it's been discussed before
 

B & S, please explain the “ Sonic Test”
Stretch

Re: 3 3/8 Too big? I know it's been discussed before
 

The fifth block that checked out to be good to use was already at 3 3/8ths. Ronnie Roadster did the build. We had to go +.030" to get the bores round. He sonic checked it before the bore and he felt confident that there was enough meat there, so we went for it. I may have just simply lucked out and the block is a 59L if that matters.

At this size, I had to get custom pistons (Ross) so I went with Total Seal rings for the reasons you mentioned. I wanted to try to have the least drag as possible since the next time this motor needs to be rebuilt, it will likely need sleeves.

Re: 3 3/8 Too big? I know it's been discussed before
 

Hi Bill give me a call when you get a chance I can guide along using the parts from Georges stash.
Ronnieroadster

Re: 3 3/8 Too big? I know it's been discussed before
 

It is a means by which to check cylinder wall thickness. Click the link below for more. DD


https://www.enginebuildermag.com/201...sonic-testing/

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Re: 3 3/8 Too big? I know it's been discussed before
 

3 3/8 was the standard oversize back in the 50s/60,s Had several blocks out to 3 7/16. One is stll running in a 40 coupe. For street a thermal expansion piston is probably the best one to run. Sometimes call steel strut pistons , they can be fit with .0005/.001 piston to wal clearance. Another piston kade by Maule)SP?) canbe run with .0015/.002 and comes in 3 5/16 X 4 rings are 1mm, 1mm 3mm. Alittle expensive at $650 a set but the Ross pistons ain''t cheep either I also Have a 296 engine 3 3/8 x4 1.8 the old fassion way with 21a rods. This engine runs an L-100 with steel sttrut pistons and ha sd ove r20K on it now. Doesn't burn a drop of oil.
Gramps

Re: 3 3/8 Too big? I know it's been discussed before
 

I'll give you a call tomorrow Ron thanks!

Re: 3 3/8 Too big? I know it's been discussed before
 

I was hoping that you would chime in ole Ron. I am working with the 21A rods and this is a 3 3/8 x 4 1/8. I got an eagle crank and Chuck Kuntz is fixing me up with a set of nos std rod bearings. This build is old school for sure. I'm looking for a set of std mains old stock
While looking through the stuff that I got from Flathead George today I found a set of thos 3 7/16 pistons!
Thanks for your input

Re: 3 3/8 Too big? I know it's been discussed before
 

When you're looking for bearings, see if he happens to have any Cadmium Silver ("For Heavy Duty Truck and Bus") versions - they're softer and easier on the crank.

Even if the crank is new, you should have mains and rod journals miced to see how good they are. I've frequently had to have them reground to .010 to get the journal dimensions, concentricity and no-taper that I wanted. Also, this allows me to tune the bearing clearances. Truth be told, on just about every new crankshaft from SCAT or EAGLE, I have them done .010/.010 - and give specific dimensions to the crank grinder.

We don't have the luxury of += .001 bearings to tune clearances, so I tend to buy .010 mains, put them in the block and then determine what the mains need to be on the crank - same with the rods. Then I give specific dimensions to my crank grinder. Anybody who has built performance flatheads will tell your that "loose is better" on the bearings - versus tight. I like .0025 to .00275 on the mains and at least .002 on the rods (on the ID) and about .002 on the OD. Make darn sure the bearings float as they were designed to do! (Hand fitting is a must).

Important: On full-floater rod bearings, you can't just throw them in and run them - they have to be setup by hand to get them to truly "float" as they should. Usually this also requires some work with a rubber hammer (to expand or pinch some shells) and then ScotchBrite and lacquer thinner to polish them. I usually try to start with about 6 sets of rod bearings - then select the "best" 4 out of the batch.

Here is a video on flathead full-floater Rod Bearings - gives you a bit of an idea on setting them up:

https://www.youtube.com/watch?v=CyVLsPdbhS8&t=15s

Here is a video showing how the crankshaft should spin if everything is correctly setup:

https://www.youtube.com/shorts/5_IkGWSIfl8

Best of luck!

Re: 3 3/8 Too big? I know it's been discussed before
 

I have my own precision sonic tester. Once a block is thoroughly cleaned and de-rusted, then I sonic test every bore - in 12 places. I write all the info down and determine what my cylinder wall thickness is. Sometimes you'll find that one side of the cylinder is thicker than the other . . . so the guy boring the block can "move the bores" around a bit to center the bore in the material.

Given that you have blocks already bored to 3 3/8, you first need to determine if the block needs to be bored again (seems that every dang one I've ever looked at does). Then you need to sonic test and pressure test it to see if you'll have enough cylinder wall thickness after the bore (or other issues).

There are many different opinions on minimum bore thickness, but for a street engine I'd sure like to see .120"+ . . . hopefully closer to .150"+ for bore longevity. With a block bored to 3 3/8, you'll probably find that the bores are between .100" to .110".

When you start going under .100", you risk "splitting" the bore when running it and also sometimes the bores move around a bit and the rings tend to wear. Another issue is that the thinner the bore, the more chances you have for a rust pocket that then requires a sleeve.

If you're re-boring a block that is already on the thin side, I highly recommend doing another pressure test AFTER you bore it - just to see if you have any rust pockets that are coming through - or other issues.

Sometimes you get lucky and you can go beyond 3 3/8, just know what you're getting into and do your best to not make the walls too thin.

Best of luck!

Re: 3 3/8 Too big? I know it's been discussed before
 

Shit

Re: 3 3/8 Too big? I know it's been discussed before
 

I actually do have some .001 and .002 bearings that came with my pile of parts. Thanks again for all the great info

Re: 3 3/8 Too big? I know it's been discussed before
 

While dealing with bearing clearances , I have to bring up side clearance as well. I increase rod clearance to .015/.020 and the floating bearing to .012/.015. Last but not least keep the oil pressure down 50lbs max. The oil pump creats a very hot oil at hi pressure the geto to the bearings. I ran a dual full flow oil filter with cooling fins on them and reduced the oil temp. Forgot how much but it surprised us.. yes I have a temp sensor in the oil pan.

Racing a Flathead back i the 60s & 770s , you were in a world of your own. No one in our area ran them any more, because the SBC replaced everything else. I was fortun enough to have a shop near by that build many of these engine and some of the guy came from the flathead ranks, they had many stories to tell. I was very new to this world and it didn't take long for me to realize why we weren't competave

Re: 3 3/8 Too big? I know it's been discussed before
 

I don't know if this will interest you. While browsing Speedway Motors garage sale site, I came across some pistons for sale at a good price. They are for a 3 3/8" bore with a stock (3 3/4") stroke. They are three ring pistons and appear to come with pins. They also appear to use the modern moly rings, which will have to be purchased separately.

Just throwing this out there.

https://www.speedwaymotors.com/Garag...ore,41569.html.