Ring end gaps
 

Brought this one up before, and never really got an answer as the thread went sideways.

I finally got out into the garage to start work on the 454's assembly. Right now, I'm measuring ring end gaps and wondering where I should be aiming. Data on this is all over the place, both here and out on the www hence bringing it up.

Current measurement shows .025 end gaps for both the top and second rings across the board. This works out to .0059 per inch of bore (based on 4.251 bore after honing).

I was thinking of taking the top ring to .028 and the second ring to .030 (.0065 and .0070 per inch respectively) to handle the blower. I've seen some discussions saying run less, others say run more. Pistons are factory 4.25 GM/TRW for which there aren't any published guidelines to reference.

What's the general consensus? Thanks!

it depends on the rings.when you buy rings they come with gap recomendation.

The instructions for the rings say to follow a minimum of .004 per inch of bore diameter.....

you are 50% above their min of .017 then. they know how much their rings expand with heat.

Tom,

What ring pack are you using? Are you employing a napier second ring?

Water temps?

Bob

Bob,

They're a Hastings 2M683 moly ring set. 5/64, 5/64, 3/16. Nothing exotic, but a good set of tried and true moly rings. I believe some may balk at the ring set used, but according to Hastings, these are supposed to be the same rings in use by Wiseco.

Water temps... I will not be running a thermostat (but will run a restrictor plate), and I boat in 70-80 degree water typically. Maybe a touch higher. Mid Atlantic... Chesapeake, ICW, five miles offshore.

Wiseco is where I got my gap figures from, but I just wanted to be absolutely sure that I'm on the right path. I could put another call into Hastings today, but bringing it up here helps to educate more people on the subject.

Thanks!

Tom, I think you'll find the water restrictor to do nothing for temps and just raise the psi in the block .

Just run it wide open then?

Adding... I did this on my small block set up, and it got my oil and water temps into a good range. Wide open it would never really warm up.

I highly recommend an oil thermostat if you don't have one. I've tried the water restrictor plates when I had the 250 blowers. They really didn't do anything except raise my water pressure too high

Got it Joe. Thanks! The oil thermostat set up is on my shopping list.

Tom,
Is the entire engine block thermally stable in the field, under load? One of your challenges (with proper gap) is addressing the Delta T, cylinder to cylinder. What is the coldest temp the coolant will see, in the case?

Bob

Does rigidity of the cylinder bore play a part in ring gaps and thermal expansion? In otherwords, would you be following the same guidelines for a dart big m 4.500 bore block as you woukd a 35 year old 454 production block that's been bored once or twice ? As far as expansion rates are concerned and maximum ring seal to bore ?

I'm not sure that I know how to answer this one, Bob. How would I know if it's thermally stable? What factors would determine that?

Nothing colder than 55 degrees, though that would only be coming out of hibernation with testing. Our water temperatures typically warm to the low 60's in the ocean by May with higher temps on the ICW and Bay (and for the most part, I like to stay on the ICW until it's warmer anyway).

Does that answer the question?

They are good rings. Use them in all the motors I have except for those damn stroker pistons in my 496 that require a super expensive rings for some reason. :cool-smiley-011:

Tom,

The delta between the water entrance/exit temp. The dimensional change in bore diameter on a 4.250" bore between 60º F and 210º can run from .002125" - .00425", depending on a number of factors. That can be exacerbated on a cylinder to cylinder basis based on localized temp variances in a thermally unstable block.

Bob

Why should you not run a thermostat in a blower motor?

Some feel that running the engine colder will help prevent detonation.

Ok, thanks. I could see that. But Let's say a low compression (8:1)454 with a 250 blower and sufficient amount of fuel being supplied with a 140-145 degree thermostat. Would that still be hazardous to possible detonation?

Yes Mild... think about it... when you have lets say a 454 with a bore of 4.310 for eg, the cylinder wall thickness (thinner) will have a significant effect on (friction surface temp) the wall's ability to cool... as opposed to lets say a dart/merlin 4.500 bore (thicker sleeve) temp is stable all around the bore and cools evenly and effectively... if I'm understanding your statement correctly???

Bob what I've been doing for years to address front to rear temp differences is bleeding off the rear ports of the intake manifold thus evening out the temp from cold front hot rear... which is a common issue with BBC

Please explain how bleeding off the rear of the intake helps to equalize temp from front to back?

the clearance in siamesed cylinders could be increased (a tad) to accommodate the extra heat, but it would be minimal at best IMO

I see, though I'm not sure of how to drum up an answer.

Incoming water temperature being 60 degrees, I don't think I'd see anything higher than 160 degrees on the gauge... so a hundred degree difference or less. That would be my target anyway. It seems that there are a number of unknowns here especially the unknowns around the unstable block factor (how would we even know if it were stable or not?). Regarding the block itself, it is clean, passed sonic checking, did not require boring to fix anything. It is a 26-27 year old seasoned piece.

-Tom

how are you getting the hot water away from the back of the engine? it allows cooling water to hit the back side of cyl #7 & 8 where it normally gets trapped

it acts as a secondary bypass... cooling water that's furthest from the incoming water seldom cools properly without said bypass

The water from the back of the block flows through the head and out the front of the intake.

And that's why I picked them up from you... btw thanks again! Everything worked out well with the pistons.

Tom,

Understood. My question was intended to determine the temperature differential, from max to min, in various areas of the block. Based on that information, running an open bore block, seeing potential 60 º min. water temp and a max bore coolant temp of 160º, I would suggest you open the gaps from .003"-.004" to compensate for the lowest internal temp.

The concept of thermal stabilization is a worthwhile conversation (for another thread), however i do not want to derail your inquiry for a viable answer to your question.

Bob

I don't run any water thermostats. My water temp coming out of my block is never more than 110*. Water going in is between 60-70 deg.

I used to run water dumps off the rear off my intakes when I had 250 blowers. When I switched to the 420 blowers I didn't drill and tap the intakes. I've been running it that way for about 100 hours now with no issues.

no visible issues...

Considering these engines have been supercharged since 1999, I am fine running without them. Mercury marine, general motors, ran without them. Not saying it's wrong to run them, as if I wasn't so lazy I would be.

Yes big Al you hit it. My concern was thermal expansion as well as the rigidity of the bore itself say at 6000rpm boosted in a production non siamese bore block. Or should I say the bores ability to maintain its shape as it would be when fitting rings on the stand fresh out the machine shop. Is that a valid concern ?

dumping a small amount of water on a siamesed block prevents steam pockets in the rear of the block,if that happens the steam will not let the water flow through the block.i see no reason to dump from the back of the block on a standard 454 block.

When I tapped mine for dumps, I mainly did it to bleed off some excessive water pressure . I felt dumping it there was better than dumping it prior to the engine .

It's not the block that gets the steam pockets it's the head. I've tested back to back dumping water out the back of the intake/ blocked off. Absolutely no difference in temp either way. This was with a Dart block. After thinking about it I would have to say that if you pull water from the back of the intake (create a short circuit in the cooling system) it would be more prone to getting steam pockets in the head than if it was blocked off. I can tell you this from experimenting that introducing cold water to the back of the intake drastically reduces detonation. If you look at some of the high dollar cylinder heads out there now they have a manifold made into the back of the head...

We haven't seen any issues running this way on the 460/B&M 250 equipped engines in the Cigarette either. One engine with well over 100 hours, and the other with between 80 and 100 hours, though these are not wild engines by any means (575 HP give or take a few).

If I was only doing the top end and didn't have the engine out of the boat, I'd probably be going that direction myself. It just makes sense to me to do it since it's all apart. Just my take on it though.

Thanks Bob! I'm all set now.

STD 454 block isn't likely to steam pocket around the rear, however bleeding a small potion off still helps even out the overall temp front to rear just my opinion... and we all know what that means!! there's another azzhole on the board!! lmfao

While on the subject of engine cooling and hot spots.....How many engines have ever been built by GM, Mercuruiser or Mercury Racing without circulating pumps?