ring end gap & courting disaster - Vintage Mustang Forums
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post #1 of 32 (permalink) Old 07-04-2019, 12:01 AM Thread Starter
LSG
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Tongue ring end gap & courting disaster

Guys, lets talk about ring end, and where it should be set if you have file fit rings,.....I believe I read that one of our men has a top ring gap of .010 and 2nd of .017,....this is less than half of whats needed ! explain yourself please, those who favor exceptionally tight ring gaps ! On our 289 & 302 engines I would like to see .030 or more.......

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post #2 of 32 (permalink) Old 07-04-2019, 12:26 AM
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On our 289 & 302 engines I would like to see .030 or more.......

LSG
.030 or more? Never seen that wide of a gap spec'd.

Allen
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post #3 of 32 (permalink) Old 07-04-2019, 01:09 AM
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Isn't the spec .010 to .020 for the top 2 rings, and .020 to .055 for the oil rings? This would put .010 and .017 in the ballpark.

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post #4 of 32 (permalink) Old 07-04-2019, 01:50 AM
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All my compression rings for the 302 out of the box were >=.016" and <.020"

Oil rings were all >.020" and <.040" out of the box

That seemed to match up with what I researched at least for a stock to street type motor.

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post #5 of 32 (permalink) Old 07-04-2019, 02:05 AM
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What kind of rings? Intended usage? Piston type? Gapless?
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post #6 of 32 (permalink) Old 07-04-2019, 06:16 AM
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Follow the manufacturers recommendations for ring gap and you will be fine. None will specify anywhere near .030" for a 4" bore motor.

Are you building a nitrous motor? Typically even they do not need to run rings that loose.

That said, running a wide cap is not as destructive as running too narrow of a gap which butts the ring ends to together and then will destructively wipe out ring lands. A very small amount of compression will be lost if the gap is on the wider side but its practically negligible.
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post #7 of 32 (permalink) Old 07-04-2019, 07:46 AM
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I am not a ring gap expert. but the 66 shop manual has this to say:
66-ring-clearance.jpg
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post #8 of 32 (permalink) Old 07-04-2019, 05:33 PM Thread Starter
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Tongue piston rings

guys, I have no idea where the .010 spec came from, but I would never run them that tight. Dennis is right on the money with this one. 50 years ago we were all taught that ring end gap was crucial, if it was too large, the engine would burn oil, lose compression and the fellow who did the work would suffer all kinds of embarrassing physical maladies. Then, sometime in the early seventies, a ring company started testing some rings with 'preset' end gaps. First they were tested at a normal gap around .020 ( never have I seen anyone try an .010 gap ), and the results, of course, were normal. Then an .030 gap was tested, then .040 and .060, with the testers hiding under the table in case the engine ate so much oil it failed and went grenade. Nothing unusual happened. The dynos couldn't even see the difference. When tested with over.125 end gap, they could see some power loss on the dyno, just a couple of percent.

I am also remembering a customer who assembled his own engine ( Chevy LS ) we knew he was going to push hard, no nitous or boost, just hard use. We suggested extra gap. He chose to listen to someone else who told him stock specs were fine, and he went to the tighter side of stock. His engine failed on the dyno in less than fifeteen minutes. over 3K destroyed.

I wonder what he thought the tight gap was going to gain him ?


Go big here, it won't hurt anything. Going small is definately a risk. If you doubt, buy a set of 2M139 rings or similar and see what gap the factory gives you now,........you'll find .020 to .030 LSG
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post #9 of 32 (permalink) Old 07-04-2019, 05:47 PM
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TBH...I thought we were all supposed to believe that you were the only engine genius here, or at least the shop where you work. What leads you to ask us...out of curiosity?
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post #10 of 32 (permalink) Old 07-04-2019, 06:13 PM
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What leads you to ask us...out of curiosity?
To show us how much more than us he knows?

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post #11 of 32 (permalink) Old 07-04-2019, 08:11 PM Thread Starter
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Tongue ring gap

PatStaple, I ask because I have vague memory of one of our men explaining in another thread that he had set his gap to .010, which is crazy tight, and I am worried for him, was hoping he would respond. Don't remember who it was, you or AllenTurn perhaps ? I'm just explaing what works, and what I know doesn't work. You can listen, or not listen to my opinion. But I'm thinking if you ask most builders, they'll tell you .004 per inch of bore, meaning .010 is clearly too tight. LSG
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post #12 of 32 (permalink) Old 07-04-2019, 08:16 PM
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PatStaple, I ask because I have vague memory of one of our men explaining in another thread that he had set his gap to .010, which is crazy tight, and I am worried for him, was hoping he would respond. Don't remember who it was, you or AllenTurn perhaps ? I'm just explaing what works, and what I know doesn't work. You can listen, or not listen to my opinion. But I'm thinking if you ask most builders, they'll tell you .004 per inch of bore, meaning .010 is clearly too tight. LSG
I've never set them that tight (.010 that is) but never as loose as .030 either. Of course I don't run any kind of nitrous or blower/super charger either...

I would have to look back but if memory serves on the 289 I'm building now, I was at .021-.022.

You asked about 289's and 302's, who knows if you mean bone stock or full blown...

Allen

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post #13 of 32 (permalink) Old 07-04-2019, 08:39 PM
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Well it wasnít me...patrickstapleR. Iíll be the first to admit Iíve not developed the balls to build a high performance engine as of yet. Iíve thrown together a couple small block Fords, but nothing for the level of abuse I intend now.

The reason I asked the question Sir is it seems as though every time someone posts a thread here regarding anything to do with an engine build, you and or ďyour shopĒ seem to have a negative opinion of it. So it sort of caught me by surprise that you actually posted a seeming question regarding an aspect of engine building. However, now it seems as Allen is correct...it appears it was only tongue in cheek.

Iíll say though...you arenít alone on that island.

Regards,
Patrick
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post #14 of 32 (permalink) Old 07-04-2019, 08:59 PM
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But I'm thinking if you ask most builders, they'll tell you .004 per inch of bore, meaning .010 is clearly too tight. LSG
Well to get to a .030" ring gap per the spec you are saying most builders will tell you, you would have to bore a 289/302 out to 7.5"...

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post #15 of 32 (permalink) Old 07-04-2019, 09:22 PM
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Ok, I'm chiming in with the specs I've been running since 2010...I can only say, it's worked for me.....
This is my spec sheet from then. Yeah, it's messy but then I'm working and posting notes at the time.
These are my numbers for bores 1 > 8
Bottom line....
Top Ring....018
Second.....020 to .025 Why?, got sloppy in my filing, I guess
3rd Oil ring .015
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