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Rebuilding the 302. First on my own build and just got the block back from the shop. .020 over bore.

Got the cam and crank installed last night with new bearings. Went to move onto the pistons today. Assembly was balanced at the shop. Running stock crank, rods w/ ARP studs, Summit Racing SUM-17370FC-20 - Summit Racing® Coated Forged Pistons, Sealed Power E-251K20 - Sealed Power Performance Piston Rings.

Was checking ring gap today. Seems like it’s all over the place and this is what I got. (Double checked)

#1. Top - .021, Bottom - .018
#2 Top - .020, Bottom - .017
#3 Top - .020, Bottom - .017
#4 Top - .021, Bottom - .017
#5 Top - .023, Bottom - .019
#6 Top - .023, Bottom - .020
#7 Top - .023, Bottom - .018
#8 Top - .024, Bottom - .020

This is a street build. Plan on eventually running boost down the road as well. Rings did not come with a reference sheet. I’ve read .004 per 1” of bore is ideal. For boost, I’ve read .005-.0055 per “1 of bore. Also I’ve read the bottom ring should be .002-.004 bigger than top ring.

My question is, did I get a bad set of rings? Bad bore job? Should I file? Swap rings around into different cylinders? Buy a different set of rings and try again?

Just want to make sure I’m getting this correct and to have a healthy motor. Thanks in advance!
 

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I don't see the problem.

Bores have a tolerance. Rings have a tolerance. Bigger is safer than smaller. Even if you carefully file-fit a set of rings, you'll have trouble doing much better than that unless you fit each ring to each bore and take all day.
 

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Discussion Starter #3
Rebuilding the 302. First on my own build and just got the block back from the shop. .020 over bore.

Got the cam and crank installed last night with new bearings. Went to move onto the pistons today. Assembly was balanced at the shop. Running stock crank, rods w/ ARP studs, Summit Racing SUM-17370FC-20 - Summit Racing® Coated Forged Pistons, Sealed Power E-251K20 - Sealed Power Performance Piston Rings.

Was checking ring gap today. Seems like it’s all over the place and this is what I got. (Double checked)

#1. Top - .021, Bottom - .018
#2 Top - .020, Bottom - .017
#3 Top - .020, Bottom - .017
#4 Top - .021, Bottom - .017
#5 Top - .023, Bottom - .019
#6 Top - .023, Bottom - .020
#7 Top - .023, Bottom - .018
#8 Top - .024, Bottom - .020

This is a street build. Plan on eventually running boost down the road as well. Rings did not come with a reference sheet. I’ve read .004 per 1” of bore is ideal. For boost, I’ve read .005-.0055 per “1 of bore. Also I’ve read the bottom ring should be .002-.004 bigger than top ring.

My question is, did I get a bad set of rings? Bad bore job? Should I file? Swap rings around into different cylinders? Buy a different set of rings and try again?

Just want to make sure I’m getting this correct and to have a healthy motor. Thanks in advance!
I don't see the problem.

Bores have a tolerance. Rings have a tolerance. Bigger is safer than smaller. Even if you carefully file-fit a set of rings, you'll have trouble doing much better than that unless you fit each ring to each bore and take all day.
Thanks for the reply. What about all the talks of the bottom ring needing to be bigger than the top? If I did 4.020 x .004 = .01608 gap minimum which all rings meet. If you do 4.020 x .005 for boost = .020 minimum which the bottom rings do not meet. I'm just curious on how crucial these numbers are over the minimum. If and when I run boost, it wouldn't be much. Around 8-10 PSI.
 

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1965 mustang 1968 mustang
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Spend the time and file fit each ring to each cylinder, do it once and do it right.
I would recommend .028" on first and second ring if you plan to run more than 7 psi of boost!
That is what I have set the last 4 boosted 302 engines that I built that were .030" over bore!
It will take you a couple hours to do with a hand file and make sure you clean up the edge so there are no bures when you are finished.
 

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0.028" is safe. You could stay at 0.024-0.026 top and 0.024-0.026 2nd ring following typical piston manufacturer recommendations.
 

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I ended up doing .024 top, .026 middle with the goal of 600 rwhp with boost and trying to avoid pressure trapped between the rings. If the end gaps meet, that's bad news bears for your piston. There is a good video out there from a guy who builds tons of boosted applications and that was the advice i found must helpful.
 

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Discussion Starter #7
Thanks for the replies everyone. Looks like I will be hand filling for a little bit! Anxious to get the motor back together but want to do it right.
 

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The first thing to remember that filing your ring one thou will increase the gap by PI (or 3 thou).

The second thing to remember is that too much end gap is fine, not enough is wery, wery bad...as Bugs Bunny used to say before the woke cancelled him.

The third thing to remember is that the second ring must always have at least .002 more gap than the top ring. Personally, I like .003

As for your motor Dwain's advice sounds about right.

As for all of it; Mark's Second Rule of Engine Building applies…."95% of engine building is opinion."
 

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The first thing to remember that filing your ring one thou will increase the gap by PI (or 3 thou).

The second thing to remember is that too much end gap is fine, not enough is wery, wery bad...as Bugs Bunny used to say before the woke cancelled him.

The third thing to remember is that the second ring must always have at least .002 more gap than the top ring. Persnallt, I like .003

As for your motor Dwains advice sounds about right.

As for all of it; Mark's Second Rule of Engine Building applies…."95% of engine building is opinion."
The other 5% is what happens if you don't have enough end gap.
 

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do .065 and .060 boost it... spray it.... run you some nitromethane up to about 45% send it and hope for the W....
 

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That's the old Speed-Pro filer...or a copy. Worked just fine. Childs and Albert have a nice hand unit, but I don't know if that carried over to Akerly and Childs.

We use one of these....

View attachment 1071787
Well arent you just a baller LOL.. Those are really nice. I dont do enough engine builds to justify one of those but i know it would have been nice doing my last engine. Using a manual one takes a lot of time.
 

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That's the old Speed-Pro filer...or a copy. Worked just fine. Childs and Albert have a nice hand unit, but I don't know if that carried over to Akerly and Childs.

We use one of these....

View attachment 1071787
I bought that one. Works awesome and rings are perfect once you get it adjusted.
 

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Discussion Starter #15
I ordered the pro form ring grinder off Amazon and comes in tomorrow or Monday. Is there a certain grooved hand file to use or will any work to get the burs? Top ring has moly face and will be sure to file from outside in and try not to flake the coating.
Sounds like this process is a “slow and steady wins the race” sort of deal. Also plan on practicing with some old rings I have laying around to get the hang of the grinder before moving to the new ones.

Appreciate all the information everyone!
 

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Discussion Starter #17
UPDATE.

Grinder came in today. It had some iffy reviews on Amazon but it worked pretty good for me. Took about 4 hours total. Top rings are set at .024 and bottom at .026. Also hit lightly with a small file on edges to de-bur. Thanks for the info everyone. Onto piston/rod install tomorrow.
 

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a friend of mine ran a dyno motor and the only change was the ring gap The power was the same until he reached around .055 ring gap so make the gap large enough so you are sure there will be no problems running boost I can only imagine how much crankcase pressure there was with a huge gap like .055
 

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65 fastback pump gas .060 289 (297) solid roller, T5 all motor. 11.12 122 mph
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The second thing to remember is that too much end gap is fine, not enough is wery, wery bad...as Bugs Bunny used to say before the woke cancelled him.

The third thing to remember is that the second ring must always have at least .002 more gap than the top ring. Personally, I like .003
Yup. I ended up with power adder ring gaps because the top ring gap was wide out of the box. Filed the second ring gap accordingly and no issues naturally aspirated. If you forget to flip the switch on your electric water pump or your electric fan you’ll be thankful you gapped them a bit wide. Tests have shown zero difference on the dyno.
 
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