Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties Flathead Pistons, Rods & Flywheels.

Flathead Pistons, Rods & Flywheels.

Moderators: Curt!, Pa

Post Thu Apr 05, 2007 6:56 am

Posts: 18
I have bought a 1938 UL motor. It does not have the flywheels, connecting rods and it will need new pistons.

There doesn't seem to be an easy availabily of pistons. I've heard that Corvair pistons will work. What needs to be done to them to use them?

From what I've been able to search on this site, the connecting rods are shorter on Flatheads. Is it true that they are labeled XA? Are they the only connecting rods that will work?

I've talked to Truett & Osborn and they will supply me with flywheels that are the right diameter for flatheads for the same price as their regular flywheels. Does this sound like the right way to go?

Post Thu Apr 05, 2007 7:20 am

Posts: 6
NOSPARTS lists 74 & 80 cid pistons, rings, and sleeves. Give them a try

Post Thu Apr 05, 2007 10:45 am
panic

There doesn't seem to be an easy availabily of pistons.
They're all over the place - every big shop carries them.

I've heard that Corvair pistons will work. What needs to be done to them to use them?
Don't.

From what I've been able to search on this site, the connecting rods are shorter on Flatheads.
Much longer.

Is it true that they are labeled XA?
No, that's OHV. Correct rod is ZA

Are they the only connecting rods that will work?
Yes.

Post Thu Apr 05, 2007 1:09 pm

Posts: 18
Thanks.

Post Thu Apr 05, 2007 2:35 pm

Posts: 6
[quote="panic"

From what I've been able to search on this site, the connecting rods are shorter on Flatheads.
Much longer.
.[/quote]

Panic is correct, OHV rods are 7.468 SV rods are 7.906 Lets agree to call it 7/16ths LONGER

Post Fri Apr 06, 2007 7:54 am
panic

The 1937-39 also has, in my experience, a slightly smaller flywheel than the 1940-48 engines, looks like 8.28" (later is 8.31").
If you're not sure 8.28" clears everything, but you generally want the largest diameter that fits for best scraper efficiency.
The Truett wheels are about the same weight as 2 right wheels (4 lbs. less than stock) if that's what you want. If you prefer stock weight you must specify TorqueMonster, which are about $50.00 more.
More: http://victorylibrary.com/stroker-flywheels.htm

Post Fri Apr 06, 2007 10:57 am
JIm

Posts: 801
Location: Planet Earth
Dukey,

Be careful with the pistons. I have had to return a few pistons I received. When I inspected them, there were visible voids in them. Looking at the inside there were pockets where the aluminum did not flow leaving a void or deep pot mark. Most were on the inside of the thrust faces of the skirt. There were also discolorations that may indicate that they did not cool down evenly or were cooled to quickly.

Another serious problem is the wrist pin locks that are supplied, they are terrible. They are made wrong, too hard or not hard at all. I do not use them but tested a few. I had two snap when being installed and a couple were loose after installation using the correct installation tool. When installed on the wrist pin and pushed against the piston by hand, they appear to expand on the back side. The way they are formed, when installed the area that would be installed towards the piston is not 90 degrees to the wrist pin. If you look at the area that installs against the piston down to where they would install into the wrist pin, it has a rather large radius rather than a sharp 90 degree bend. This coupled with the back not being 90 degrees might tend to pop it off the wrist pin.

I use OEM wrist pin locks on them, some of the wrist pin grooves are slightly narrower than the HD locks so the locks need to be narrowed slightly. The real OEM locks are still available from some of the dealers both HD and others.

I have had good luck with Eastern pistons, but their locks have the same problems.

Jim


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