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Discussion Starter #1
Hi guys,
I measured piston ring end-gaps and some were too large, including all the oil rings. I have standard bore diameter. Any advice here ?


Some gaps were significantly over spec, including all the oil rings (yes, I measured them far down in the bore, not at the top).

Too small end-gap is way worse than too large, but have a look at these measurements....


#1 compression ring gaps are averaging around 0.016" which is close enough to spec.

#2 compression ring gaps are averaging around 0.019" which is within spec, but one ring is 0.023" and another is 0.039" ! I tried moving these rings to different cylinders.... and its due to that ring being small, not a large cylinder.

Oil ring end gaps are averaging around 0.037" which is way larger than spec.


'82 - '83 specs are:
#1 spec = 0.0083" - 0.0146"
#2 spec = 0.0067" - 0.0209"
oil ring spec = 0.0079" - 0.0276"


Here's that #2 ring with the really large 0.039" gap, you could drive a bus thru there. The cylinder above shows a normal gap.


I'm happy with all the #1 gaps and and those are the most important, but the oil ring gaps are way over, and a couple #2 ring gaps are way over also. These are a Beck/Arnley ring set 013-3867. I don't think my bores are worn out, the machinist said there wasn't much wear.

How big a problem is this ? Seems like the oil rings may not be that big a deal. Should I buy another set of rings to replace some of the short #2 compression rings ?
Thanks
 

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WELLLL...what we used to do in Ye Dayse Of Olde was to buy oversize rings and file them down until the gap was in spec. Some guys even had a little machine to grind them down so the end-gaps came out right.

I don't know how consistent the rings are out of the package. "Standard" size rings might be all over the map. Have you tried swapping them around in different cylinder bores? I'm guessing that won't matter because the bores should all be the same size +/- almost nuttin'.

I agree that the gap on the oil rings isn't that important. As long as you place the gaps 180* to each other, they should scrape the oil off the wall OK.

#1 ring is critical, and the #2 ring almost as much.

One thing I was always told told was to err on the side of slightly larger gaps. If the ends of the ring butt together, you'll get a broken ring almost instantly, and that's A Bad Thing!
 

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Looking at those pix closely, I have to ask:

Was this block bored oversize and honed?

Something about those cylinder bores just looks "funny".....almost like they weren't bored, just honed.
 

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It's not normal to have that much variance in your 2nd ring end gaps. If it were my engine, it would make me question the entire ring pack and I probably wouldn't use them. I've never used Beck/Arnley rings (and I've built ~500 engines) but I'd be surprised if you had these issues with rings from Hastings or Enginetech.

Also, it's good practice to check ring end gap over the entire cylinder bore when you're doing a re-ring job such as this. Its good to know what the ring end gap is at the top of the cylinder as that is where your compression is made. You're not going to like the number because your cylinder is worn there (you can see the ring impressions) but at least you know what it is.
 

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Discussion Starter #6
It's not normal to have that much variance in your 2nd ring end gaps. If it were my engine, it would make me question the entire ring pack and I probably wouldn't use them. I've never used Beck/Arnley rings (and I've built ~500 engines) but I'd be surprised if you had these issues with rings from Hastings or Enginetech.

Also, it's good practice to check ring end gap over the entire cylinder bore when you're doing a re-ring job such as this. Its good to know what the ring end gap is at the top of the cylinder as that is where your compression is made. You're not going to like the number because your cylinder is worn there (you can see the ring impressions) but at least you know what it is.
These Beck/Arnley rings were the least expensive, so you get what you pay for I guess. I thought it was a good quality brand.
Also its weird that these rings don't have markings on them to indicate which side faces upwards, maybe they're bi-directional. The original rings had markings, 1T & 2T.

I'll check the gap along at different depths in the bore like you suggest.
The bores show ring impression markings near the top, but they aren't really deep, I cant feel them with my finger. They show up visually more prominently after the hone.

I'd hate to have to buy another ring set, but if I must I will. Enginetech rings are available at rockauto.com, and are listed as a premium set.
 

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Discussion Starter #7
WELLLL...what we used to do in Ye Dayse Of Olde was to buy oversize rings and file them down until the gap was in spec. Some guys even had a little machine to grind them down so the end-gaps came out right.

I don't know how consistent the rings are out of the package. "Standard" size rings might be all over the map. Have you tried swapping them around in different cylinder bores? I'm guessing that won't matter because the bores should all be the same size +/- almost nuttin'.

I agree that the gap on the oil rings isn't that important. As long as you place the gaps 180* to each other, they should scrape the oil off the wall OK.

#1 ring is critical, and the #2 ring almost as much.

One thing I was always told told was to err on the side of slightly larger gaps. If the ends of the ring butt together, you'll get a broken ring almost instantly, and that's A Bad Thing!
Jim, I tried swapping the 'bad' rings around to different cylinders, but the gap remains large on those rings. Pretty sure all my bores are the same size +/- almost nuttin'.

I thought the rings would come out of the package too long, and that they could be filed down to fit. In this case there's nothing I can do to make them longer.

I thought that filing down over-size rings which have a different diameter will result in an oblong ring, not perfectly circular.
 

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I've ordered lots of parts from RockAuto and been very happy with their quality and prices. There were however a couple of times that I received incorrectly packaged parts from them - the part inside the box was not what was labelled on the box.
 

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Discussion Starter #9
I'm learning these things as I go, and I've read that chrome rings are better for turbo (which I'd like to do in the future); the 7MGTE uses chrome rings.

I've also read that fresh re-bored cylinders can use chrome rings, but used bores should use cast rings.

Apparently there are 3 types of rings, moly, chrome & cast.
Moly rings will have a shiny grey OD; chrome rings will have a shiny silver OD and the cast rings will be black in color on all surfaces.



The beck/arnley has cast (black on all surfaces) #2 rings..... the #1 rings are shiny grey on all surfaces, so those must be moly.
 

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"Moly" rings have a coating of Molybdenum them. AFAIK, they're just specially treated cast-iron rings. They used to make the face of the ring concave, and fill that depression with Moly which formed the actual sealing surface of the ring. It's been many, many years since I built engines, so I wouldn't be surprised if the technology has changed. They seat very fast compared to chrome-plated rings, which are harder on the cylinder walls.

No experience with supercharged engines, so I can't comment on what type of rings are "better".

All the rings I've ever used were marked with a dot that indicated to "top" side of the ring. I've always bought Perfect Circle or Hastings rings.

I don't think filing the ends gaps will make the rings go out-of-round enough to worry about. It's always been "standard practice" even with the guys that bore and hone with deck plates to make the cylinders extremely round once the head is torqued on the block.

As far as incorrectly marked boxes from Rock Auto, Christina (black MKII from AZ) had a rant on her FarceBook page about getting a load of bum injectors from Rock Auto. So far I haven't had that happen, but now I'm inspecting each package I get from them very closely.
 

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I have a great (HORRIBLE) idea.

File all the ring gaps to the large size so they match
Do the same for the oil rings (to their max size)
Get some low compression pistons out of an old 82 / 83 5M

Now add 24 to 30LBS of boost; now your ring gaps will narrow up but not get too tight.

See clearly a bad idea to tighten up the ring gaps.
 

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Discussion Starter #15
I've ordered lots of parts from RockAuto and been very happy with their quality and prices. There were however a couple of times that I received incorrectly packaged parts from them - the part inside the box was not what was labelled on the box.
Damn Rockauto just screwed me again, my main bearings were packaged incorrectly. All 14 pieces had the oil groove & oil holes. It should've had 7 of the pieces flat (no oil groove/holes).
like these


I was over the 30 day return period........ so the website wouldnt let me return....... called then they agreed to re-ship them, and at first wanted me to return the defective part at my own cost, then agreed that I dont have to ship back the defective part. Not bad in the end, but annoying

The moral of the story is to carefully inspect your order as soon as it arrives.
 

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Actually, most builders prefer all bearing shells to have the groove. You got lucky and got that without having to buy 2 sets of mains. Up to you how you want to assemble it though. Rock auto doesnt pack the bearings however. They should have all been vacuum sealed to a cardboard backing in the package.
 

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Discussion Starter #17
Oil grooves in both halves of the bearing ?!?! I didn't realize that was even a possibility. I thought the lower bearing half was always flat/smooth because that's the loaded side of the bearing.

Your right, it wasn't Rockauto's fault, the manufacturer packaged these wrong. Rockauto will take this matter up with the manufacturer if they feel so inclined.

The box came with two sets of 7 bearing halves each vacuum sealed separately, and thus the possibility for packaging mistakes. These were EngineTech BTW.

I'm holding my breath that the new set is correct.
If I'm lucky the new set will totally without grooves, and I can assemble 2 full sets with both.
 

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I don't know if full race main bearings are still fully grooved on both halves. But they certainly were from the 60's to the 80's. This was for various flavors of NASCAR motors. The bottom half being solid for load bearing does make sense though, which is probably why most engines don't use fully grooved mains. My understanding was that the full grooves helped in keeping sufficient oil to the rod bearings. But this was back when the best racing oils all still sucked. At some point they all essentially ended up becoming a wall of oil being pushed by the journal. It takes about as long to visualize that as it would last in the real world. Lucky us. Even the crappiest oils being made today are worlds better than those were!
 

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Fully-grooved bearings have been in and out of favor for years. A lot of it depends on the original design of the engine; bearing surface area vs bearing loading vs engine output.

For our 5M engines, I'd go with whatever the original design was.
 

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Discussion Starter #20
Well the stupid new set of bearings I received today are also full-groove. Don't think this is correct.

I checked the manufacturer website and its pretty clear the upper and lower shells should be different. Each half shell has a unique P/N, and the picture shows half-groove.

Shell P/N .......... Position
M1-1051-L ........ 1-2-3-4-5-6-7
M1-1051-U ....... 1-2-3-4-5-6-7

Where else can I get some 0.25mm undersized main bearings ? Reasonable shipping to Canada is usually a problem.
 
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