Flathead Piston and Ring Questions...

Jay Ess

Jay Ess

Member
Guys over at the HAMB suggested I post this here.

I am rebuilding my stock 51 Merc Flathead. I will need to replace pistons and rings and may have to bore it 1 size over depending on what I hear from the machinist. I have been using the search function and have researched the available suppliers and still have many questions regarding which piston/ring combination to use.

Why would one use a 3 ring vs. 4 ring setup?

Are there differences in brands? Egge, Speedway, Ross, Hypermax –Hypereutectic (whatever that means).

If I never plan to run a blower do I need forged pistons or is that over kill?

I would like to buy American if that makes a difference.

Any other guidance would be appreciated

Thanks, js
 
One more thing to consider: in 1951 the piston pin was offset. This was done to even out piston side loads and to reduce piston noise. The quietest flatheads I have heard have the late rotating exhaust valves and the offset piston pin.

You don't want forged. They are overkill unless you are racing or using a blower. They require more wall clearance. Thus you spend more money to have a noisier engine that uses more oil.
 
I'd use EggE 3 ring pistons, they are reasonably light, can be fit tight and use a modern ring. Been using them for years. I'd also bore .125 over, but that's me. it will raise the CR almost a point and add 19ci to your engine (258) Have fun.
 
One of my flatheads has the 4 ring piston and the other has Ross 3 ring with the 1.5, 1.5, 3.0 mm rings. The 4 ring engine is a lot harder to turn over with the fan than the 3 ring so must be less drag and friction and less heat from the friction but the Ross piston's are noisier for sure.

Vergil
 
Thanks for the responses! Vergil when you say the 3 ring pistons are louder, are you referring to piston slap?
 
Ol' Ron said:
I'd use EggE 3 ring pistons, they are reasonably light, can be fit tight and use a modern ring. Been using them for years. I'd also bore .125 over, but that's me. it will raise the CR almost a point and add 19ci to your engine (258) Have fun.
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Thanks! That is the type of feedback for which I am looking.
 
I'm doing the same thing right now. My 255 had some cylinder pits. The machinist said it should clean up at .060. I told him go to .125. Same price to go .125 as .060. I want a little more snoose. I bought Egge oistons from Speedway $250. Some say Egges are junk. My builder is 70 years old he says he's never had any problem with going .125 or Egge pistons. He said rings a pistons have improved over the years and 3 ring is fine.

Ol Ron should know what he's talking about also. Go for it, this is hotrodding. Gene
 
Jay Ess said:
If I never plan to run a blower do I need forged pistons or is that over kill?
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No
In my opinion forged pistons are the way to go if you can afford them.

I believe my machinist told me that forged nowadays don’t need the massive clearance the old ones did.

Almost every time Iv cheeped out and used cast it has bit me in the A$$.

And by the look of many a flathead iv torn down that had cracked pistons….im sticking to my belief.

I run ROSS in the ~V8~'s....so far so good.
 
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I have to disagree. Forged pistons are overkill for a street engine and no way can they be fit as tight as a cast piston.
 
Jay Ess said:
Thanks for the responses! Vergil when you say the 3 ring pistons are louder, are you referring to piston slap?
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Thats correct Jay, when I had it bored the piston instructions that came with the pistons gave the clearance to shoot for on final honing but the machine shop said they were to tight so they called Ross tech and they also said to give them a little more clearance than the sheet said for the flathead. With the extra clearance, very thin rings and no offset on the piston pins I can hear them. Doesn't bother me to much but for those who wants to hear it run I always try to get the piston noise into the conversation before starting it ;).

Vergil
 
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To each his own, The Egge Piston is cast fron a hi Silicone Aluminum which allows a tighter fit. I've been fitting then at .002" and so far nobody has had any trouble. I have Ross pistons in several street engines set at .004 and they don't make any noise when warm.
 
38 coupe said:
One more thing to consider: in 1951 the piston pin was offset. This was done to even out piston side loads and to reduce piston noise. The quietest flatheads I have heard have the late rotating exhaust valves and the offset piston pin.
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Learn something every day! Are pistons with the pin offset still available and if so, from whom? Is this something I should use? How would I know if the pistons I have pulled are offset? I would presume that one would not be able to tell visually, or are there factory markings? I was told the engine was a 51 but do not know if that is correct. Once again, Thanks for the info and education! J
 
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Pistons with an offset pin will have a mark on top of the piston pointing to the front. No mark = no offset.
 
quickgene said:
I'm doing the same thing right now. My 255 had some cylinder pits. The machinist said it should clean up at .060. I told him go to .125. Same price to go .125 as .060. I want a little more snoose. I bought Egge oistons from Speedway $250. Some say Egges are junk. My builder is 70 years old he says he's never had any problem with going .125 or Egge pistons. He said rings a pistons have improved over the years and 3 ring is fine.

Ol Ron should know what he's talking about also. Go for it, this is hotrodding. Gene
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Thanks Gene. More great info...
 
You can run Ford 239 pistons with a 4 inch crank if you buy the French 6 7/8" con rods. Woops another $200 frog skins.
 
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