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ring gap setting


zimm

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On a stock bore L20B (per the FSM)

Top ring gap......... 0.0098" to 0.0157"
Second ring gap... 0.0118" to 0.0197"



I found an on line site that specified 0.0044" for every inch of bore for the top ring... I got 0.0133" end gap
For the second ring 0.0055" for every inch of bore and I got 0.018" gap. Close enough for a stock use engine.

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That will work as they all will. A tighter tolerance seals the compression better but on the down side if ever over heated, risk the gap closing and the rings or lands breaking. This would be an extreme case however caused by owner ignorance or running a turbo which isn't expected here. I've pulled many pistons with broken rings but usually they had either seized or had a rod through the block.

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I found an on line site that specified 0.0044" for every inch of bore for the top ring... I got 0.0133" end gap

For the second ring 0.0055" for every inch of bore and I got 0.018" gap. Close enough for a stock use engine.

 

This is the rule I have always used as well. Have yet to have a failure. 

Keep in mind that, like Mike stated, THIS IS FOR A STOCK ENGINE. If your are using any type of power adder like a turbo, super charger or nitrous, this gap will need to be bigger. 

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  • 8 years later...

Necro-posting a related question.

 

I bought 85.5mm pistons and rings for an L20B. I got the block bored to match the pistons. The bore is pretty much on the money at 85.5mm. I got Hastings rings (Part#: 6872-020) which are for 020 over pistons and the top ring gap is coming in at .51mm. The stock bore spec is .25 to .40mm. Various websites state they should be between .0044 - .0065 per inch of bore, minimum. I'm a little over the spec for the max spec on a stock bore. Second ring and oil rings are within spec.

 

How big of a concern is this? Should I try to locate 4 replacement top rings?

 

This is just an NA street motor. Nothing special.

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Top ring is 0.0044 per inch of bore. For an 85.5mm bore that's 0.376mm

Bottom ring is 0.0055" per inch of bore. An 85.5mm bore that's 0.47mm

 

Perhaps you have stock 85mm rings???? they would be smaller and have more gap.

 

I would prefer 0.37mm ring gap than 0.51mm. That just under 40% too large a gap. It will work of course but the wider the gap the more blow-by.  Ideally no ring gap, but that 0.37mm is the minimum safe limit for expansion from heat. If there is no room for expansion the ring lands and the rings can break.

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1 hour ago, datzenmike said:

Top ring is 0.0044 per inch of bore. For an 85.5mm bore that's 0.376mm

Bottom ring is 0.0055" per inch of bore. An 85.5mm bore that's 0.47mm

 

Perhaps you have stock 85mm rings???? they would be smaller and have more gap.

 

I would prefer 0.37mm ring gap than 0.51mm. That just under 40% too large a gap. It will work of course but the wider the gap the more blow-by.  Ideally no ring gap, but that 0.37mm is the minimum safe limit for expansion from heat. If there is no room for expansion the ring lands and the rings can break.


I sent an email to Hastings tech support. The box is marked 020 over, but who knows. I was thinking the same thing.. maybe the wrong top rings. 

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16 hours ago, datzenmike said:

From the factory the stock bore can be up to 85.035mm.

 

0.5mm over would be 85.535mm and should be checked in case it was over, over bored by mistake.


I measured it, but I’ll break out the precision tools to confirm the exact size.

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Well in a strange turn of events, Hastings replied to my email with an alternate part number for a file to fit top ring. They don't sell directly to the public to they gave me the phone number to Total Seal. I called total seal and after giving them the bore and the part number they confirmed the part to be SMALLER than the original ring, which would have given me an even bigger gap they said. So I bought 4 Total seal top rings (for the price of of more than a complete set mind you....) These rings are file to fit, so I'll get it them dialed in and all should be well. I hope.

 

Could I have just bought rings for a 86mm bore and filed the end gaps down? Seems like it'd work also. Either way Total Seal was great, I'll have the part in 3 days.

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On 8/12/2023 at 10:17 PM, Draker said:


I measured it, but I’ll break out the precision tools to confirm the exact size.


measured, it was spot on at 85.5. They took the measurements off each piston and bored to match. 

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