Question on Piston Ring Gap
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Topic author - Posts: 14
- Joined: Fri Apr 05, 2019 4:52 am
- First Name: Markus
- Last Name: Huether
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Question on Piston Ring Gap
Hello together,
I use Aluminium Pistons in my 26 Roadster with .040 oversize and the Grand Rings for Aluminium Pistons .040. The standard Gap for the rings is 0.004-inch per inch of diameter of the cylinder. That means 0.004 x 3.790 = 0,015.
My question is now, what is the maximum accept gap for this combination? is 0,024 to much???
Thanks from Germany
Markus
I use Aluminium Pistons in my 26 Roadster with .040 oversize and the Grand Rings for Aluminium Pistons .040. The standard Gap for the rings is 0.004-inch per inch of diameter of the cylinder. That means 0.004 x 3.790 = 0,015.
My question is now, what is the maximum accept gap for this combination? is 0,024 to much???
Thanks from Germany
Markus
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Re: Question on Piston Ring Gap
I think that's too much. I was advised by the guys at Grant to use the next over size rings and then you can get the proper gap.
1912 Torpedo Roadster
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Re: Question on Piston Ring Gap
0.012" is what I set a fresh rebore rebuild on a T but according to the likes of Hastings web site, max can be .022" to .026" for around a 4" bore, give or take 1/2"
If your new rings are giving you that much gap and are the right size for the pistons then what are your pistons giving you in the bore?
If your new rings are giving you that much gap and are the right size for the pistons then what are your pistons giving you in the bore?
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Re: Question on Piston Ring Gap
I think .012” is a little tight for the top ring, okay for the oil ring though.
I’d not worry about a little extra ring gap in the top ring, put it together.
I’d not worry about a little extra ring gap in the top ring, put it together.
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Re: Question on Piston Ring Gap
Aaron,
to some it may seem a tight spec but for 45 years of engine rebuilding never any issues, even by the book which is a min of .003" per inch. Even at .012" is still just over the min on a 3.750" T bore.
By the way the spec book I've used all those years, (Digest of Automotive Engine Re-Conditioning) is a max of .005" per inch, unless ring makers specs say different.
to some it may seem a tight spec but for 45 years of engine rebuilding never any issues, even by the book which is a min of .003" per inch. Even at .012" is still just over the min on a 3.750" T bore.
By the way the spec book I've used all those years, (Digest of Automotive Engine Re-Conditioning) is a max of .005" per inch, unless ring makers specs say different.
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Topic author - Posts: 14
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Re: Question on Piston Ring Gap
Thanks for the answers.
I want to explain, why i asked the question:
I got a complete rebuild motor. I put the motor in a teststand to run the motor to see that the motor is running fine. After about 10 minutes run (motor is running fine), i removed the sparkplugs. The sparkplug from the first cylinder was complete black with a oil film. The others are fine. So i removed the head and i found this:
The Pistons are Aluminium with 0,040 oversize.
Than i start to investigate what is the problem. I removed the first Piston to see where are the gaps located from the Pistonrings. That was fine.
Then i checked the installation direction of the piston (Wrist Pin goes toward the cam. The slot in the Piston goes away from the Cam). That was fine.
Than i started to measure. Here are the results:
Top Pistonring 0,026 Gap
Middle Pistonring 0,022 Gap
Oil ring 0,020 Gap
Gap from the piston rings in the piston groove 0,002
Piston: Diameter from the Piston bore 3,791.
When i put the feeler gauge in (Piston in the piston bore without Piston rings) there is a Gap from 0,008.
I will now remove the second piston to measure it.
what is your opinion?
Markus
I want to explain, why i asked the question:
I got a complete rebuild motor. I put the motor in a teststand to run the motor to see that the motor is running fine. After about 10 minutes run (motor is running fine), i removed the sparkplugs. The sparkplug from the first cylinder was complete black with a oil film. The others are fine. So i removed the head and i found this:
The Pistons are Aluminium with 0,040 oversize.
Than i start to investigate what is the problem. I removed the first Piston to see where are the gaps located from the Pistonrings. That was fine.
Then i checked the installation direction of the piston (Wrist Pin goes toward the cam. The slot in the Piston goes away from the Cam). That was fine.
Than i started to measure. Here are the results:
Top Pistonring 0,026 Gap
Middle Pistonring 0,022 Gap
Oil ring 0,020 Gap
Gap from the piston rings in the piston groove 0,002
Piston: Diameter from the Piston bore 3,791.
When i put the feeler gauge in (Piston in the piston bore without Piston rings) there is a Gap from 0,008.
I will now remove the second piston to measure it.
what is your opinion?
Markus
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Re: Question on Piston Ring Gap
Is there an outside oil line over feeding #1 ?
Forget everything you thought you knew.
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Topic author - Posts: 14
- Joined: Fri Apr 05, 2019 4:52 am
- First Name: Markus
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Re: Question on Piston Ring Gap
Yes, there is an outside oil line.
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Topic author - Posts: 14
- Joined: Fri Apr 05, 2019 4:52 am
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Re: Question on Piston Ring Gap
Hi together,
Does anyone have an idea for this topic????
Does anyone have an idea for this topic????
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Re: Question on Piston Ring Gap
Might check position of the rings on that piston. Had one rebuild that fouled #1, valves were ok, but pulled the piston and found one ring up-side down and the taper was pushing up the oil.
Used a hone and scuffed the bore, replaced the ring correct side up, put piston back, and no more issues.
Used a hone and scuffed the bore, replaced the ring correct side up, put piston back, and no more issues.
The best way is always the simplest. The attics of the world are cluttered up with complicated failures. Henry Ford
Don’t find fault, find a remedy; anybody can complain. Henry Ford
Don’t find fault, find a remedy; anybody can complain. Henry Ford