Ring Gap for New Speed Pro L2255F40???

[BPBP440]

Ring Gap for New Speed Pro L2355F40???

Bought an engine rebuild kit from Summit, which included a standard fit ring set for .040 over 440 (4.360). The ring set is ZE424K40, cast iron moly coated top ring, cast iron non coated 2nd ring. I am surprised at the ring end gap, which is .035-.036 consistently across all cylinders.

I did read previously that some of the newer pistons are running significantly larger end gaps, but I do not know if these pistons fall into that category. Summit tech line gave me the standard .004/inch of bore, without hesitation or looking anything up.

Any experience you can share with these pistons and appropriate end gaps would be appreciated.

Jim

 

[Meep-Meep]

It really depends on the alloy the pistons are made of. Hypereutectic pistons have more silicon than can normally be put into aluminum (hence the name) and those require a larger gap because of poor thermal conductivity. It's a 4000 series alloy as opposed to a 2000 series of a forged piston. Summit doesn't make anything so likely sourced them from Silvolite or some other piston manufacturer. You might call back and see if you can get better info.

- - - Updated - - -

Duh, the title says Speed Pro. Call them directly and see what they say. I was thinking this was some Summit brand piston. They have cams and other stuff...

 

[69Bee]

Bought an engine rebuild kit from Summit, which included a standard fit ring set for .040 over 440 (4.360). The ring set is ZE424K40, cast iron moly coated top ring, cast iron non coated 2nd ring. I am surprised at the ring end gap, which is .035-.036 consistently across all cylinders.

I did read previously that some of the newer pistons are running significantly larger end gaps, but I do not know if these pistons fall into that category. Summit tech line gave me the standard .004/inch of bore, without hesitation or looking anything up.

Any experience you can share with these pistons and appropriate end gaps would be appreciated.

Jim

Looking at summit, I can only find ZL2266F40 and ZL2355F40 listed for the motor specified. The piston clearance is 0.0015", but really depends on your desired usage for the motor, and the same goes for the rings. For a hot street setup, I wouldn't be afraid to run them at 0.002" to 0.0025" for the clearance.

The ring gaps are dictated by the motor, desired usage, and piston type to determine the ring gaps. You didn't say whether the bores were just bored and honed, but I will assume they were. If the machinist honed them over the required 0.0015", the ring clearance will open up. With stock numbers, you are looking about 0.014" to 0.022", and for a HP street motor, you can open it up to say 0.018" to 0.026". I have seen some go up the what you are seeing, and although you might have a little more blow-by, you wont really see any difference on the street. You would see a difference if you were racing and every tenth counted. Hope this helps.

Dave

 

[BPBP440]

Looking at summit, I can only find ZL2266F40 and ZL2355F40 listed for the motor specified. The piston clearance is 0.0015", but really depends on your desired usage for the motor, and the same goes for the rings. For a hot street setup, I wouldn't be afraid to run them at 0.002" to 0.0025" for the clearance.

The ring gaps are dictated by the motor, desired usage, and piston type to determine the ring gaps. You didn't say whether the bores were just bored and honed, but I will assume they were. If the machinist honed them over the required 0.0015", the ring clearance will open up. With stock numbers, you are looking about 0.014" to 0.022", and for a HP street motor, you can open it up to say 0.018" to 0.026". I have seen some go up the what you are seeing, and although you might have a little more blow-by, you wont really see any difference on the street. You would see a difference if you were racing and every tenth counted. Hope this helps.

Dave

Dave,
You are correct, they are 2355F40 pistons. I tried to go the file fit route. Well Summit has nothing that is file fit for 5/64, 5/64, 3/16 , 4.360, expect they did find a Ford 429 file fit ring set (Sealed Power R 102465) that had to be special ordered. After contacting Sealed Power, they found out it was discontinued.

Piston clearance is .0045 based on engine builder advice on this board, which was echoed by the shop that did the machine work. I may have to go with the .036 gap I have, but I sure do not want smokey exhaust.

 

[69Bee]

Dave,
You are correct, they are 2355F40 pistons. I tried to go the file fit route. Well Summit has nothing that is file fit for 5/64, 5/64, 3/16 , 4.360, expect they did find a Ford 429 file fit ring set (Sealed Power R 102465) that had to be special ordered. After contacting Sealed Power, they found out it was discontinued.

Piston clearance is .0045 based on engine builder advice on this board, which was echoed by the shop that did the machine work. I may have to go with the .036 gap I have, but I sure do not want smokey exhaust.

I did some checking today, and all of the file fit sets are non-existent for the 5/64" pistons. People are going for the 1/16" pistons now. Anyway, after a few calls, and about an hour of research, I can get you a custom ring set from Total Seal.

The ring set consists of the following:

Top Ring 0.045" os (Moly file fit)
2nd Ring 0.040" os
Oil Ring 0.040" os

I can have it drop shipped from the manufacturer to me, then I ship it to you. The cost would be $132.93 plus shipping. No tax as it would be out of state. If you are interested, you can PM me your info so we can complete this. The ring set is in stock, and my quote will stay for a few weeks, so let me know if you are interested.

Dave
Precision Machine Service

 

[Garys1969RR]

Now I see why they recommend a .035 over size bore on the 400 block. That makes for a 4.375 bore, and is more common than the 4.360 bore you have.To get this bore size in a 440, you would have to go .055 O.S. And that is really pushin it I think. I want the thicker cyl walls. Yea .035" ring end gap is definitely too much.

 

[BPBP440]

Thanks for taking the time to help me out today. Really do appreciate it.

Talked to Hastings. They had a set of 4.370 on the shelf for a Olds 403, and considering my bore is 4.365...that should be perfect for file fit.

Red Saturday delivery and I am in business.

Thanks for all the help today.

Jim

 

[69Bee]

No problem, and good luck with it.