Re-ring sour cylinder?

[SoCar72]

My #4 cylinder has very weak compression and I have a lot of blow-by in the crankcase leading me to conclude that the rings have given up the fight. I had the head off a few months ago to replace the head gasket. The head's in great shape : valves, seats, etc:.

Ideally, I want to replace the 4-main 170 with a rebuilt/reman 7-main 200 or 170. Financially that's not in the cards for at least 6 months.

Thinking about just re-ringing that one cylinder to keep her on the road until I can go all out on the engine. I've heard of people doing this but never heard any follow-up. Has anyone done this with respectable success?

 

[rbohm]

8) i have reringed and rebearinged engines in the past with no issues. one thing you need to do though is replace the rings on all cylinders, not just one. that way you dont have to go back and rering another cylinder in a few weeks or so. also do NOT use chrome rings when doing this, use cast iron rings instead as they break in quicker.

 

[Thad]

And de-glaze all cylinders with a dingle-berry hone. At least 10 strokes, Moving up and down quickly to get a +/- 45 deg hatch. each

 

[wsa111]

My #4 cylinder has very weak compression and I have a lot of blow-by in the crankcase leading me to conclude that the rings have given up the fight. I had the head off a few months ago to replace the head gasket. The head's in great shape : valves, seats, etc:.

What are your compression readings in all cylinders.
If all the compression readings in the other cylinders are over 125#'s then a mickey mouse fix would be a temporary repair.

If you just plan to keep the present engine for several months then just do the one cylinder. As previously stated use cast iron rings & a dingle-berry hone 380 grit.

ALL DEPENDS WHAT THE COMPRESSION OF THE OTHER CYLINDERS ARE??????

If others are below the 125-115 area you better do all cylinders.

You have a good chance of a scored cylinder wall & or cracked rings or broken ring lands in the low cylinder.

I personally do not recommend this repair, but do what you have to do. Bill

 

[SoCar72]

Re-ringing all 6 sounds like the way to go. Assuming that the walls aren't scored, it would be a little counter productive if suddenly 4 becomes the strongest cylinder. I didn't notice any scoring when I had the head off, I looked specifically at 4 for such damage.

Thanks for the advice.

 

[bubba22349]

A re-ring kit will be cheaper than ind. parts, includes rings, gaskets, and the rod bearings. Than you can also add mains and oil pump etc.

 

[80broncoman]

8) i have reringed and rebearinged engines in the past with no issues. one thing you need to do though is replace the rings on all cylinders, not just one. that way you dont have to go back and rering another cylinder in a few weeks or so. also do NOT use chrome rings when doing this, use cast iron rings instead as they break in quicker.

X2 and if your rear main seal doesn't leak leave the rear main cap, bearing and seal alone.
And do not take all the other main caps off at one time. If you do that you will kill the rear main seal for sure.

 

[Thad]

You may have to run a ridge reamer it there is a ridge or it will break new rings.

 

[SoCar72]

I finally got around to a real compression test. I was wrong about the 4th cylinder. I suspected it because of the deposit build-up. As it turns out, #2 is the sour one :

1 @ 145psi
2 @ 50 psi
3 - 6 @ 150 psi (all rounded to the nearest 5)

The firing order explains the build-up in 4 since 2 is on its compression stroke and blowing hard through the PCV while 4 is on its intake stroke. Add that 3 and 4 are closest to the carb hole and closest to the PCV inlet in the carb spacer, it seems logical that 4 will pull the bulk of 2's blow-by.

I doubt it is a burned valve or piston since they both looked very good when I had the head off some months back replacing the head gasket. With the heavy blow-by into the crankcase it seems that the rings are the culprit.

Being that the other 5 cylinders are so closely matched (Motors Manual says that +/- 20 psi is tolerable and I'm within about 5) I'm rethinking about just re-ringing #2 and leaving the others alone. If the variance was greater there'd be no question about re-ringing all 6.

Thoughts?

 

[rbohm]

I finally got around to a real compression test. I was wrong about the 4th cylinder. I suspected it because of the deposit build-up. As it turns out, #2 is the sour one :

1 @ 145psi
2 @ 50 psi
3 - 6 @ 150 psi (all rounded to the nearest 5)

The firing order explains the build-up in 4 since 2 is on its compression stroke and blowing hard through the PCV while 4 is on its intake stroke. Add that 3 and 4 are closest to the carb hole and closest to the PCV inlet in the carb spacer, it seems logical that 4 will pull the bulk of 2's blow-by.

I doubt it is a burned valve or piston since they both looked very good when I had the head off some months back replacing the head gasket. With the heavy blow-by into the crankcase it seems that the rings are the culprit.

Being that the other 5 cylinders are so closely matched (Motors Manual says that +/- 20 psi is tolerable and I'm within about 5) I'm rethinking about just re-ringing #2 and leaving the others alone. If the variance was greater there'd be no question about re-ringing all 6.

Thoughts?

well, if you can find a parts store that will sell you a set of rings for just one cylinder, more power to you, but since you will have the engine partially torn down to rering one cylinder, you may as well do them all, because if you have a broken ring on cylinder number two, chances are that the other rings have as much wear and tear.

 

[wsa111]

Since #2 is the weak one, make sure the valves are in there closed position & put 75-125# of compressed air into #2 cylinder.

You will find out real fast what your problem is.
Air blowing out the carb, intake valve problem, air out the exhaust, exhaust valve problem, air in the radiator, blown head gasket or something cracked, & air out the breather, broken rings & or piston damage.

If the problem is downstairs, as recommended by others do all the cylinders. Bill

 

[SoCar72]

Rbohm : Good point. After I posted I got to thinking what if, assuming I only re-ring 2, suddenly 2 is testing well above the other 5? Better than #2 @ 50psi, but still an imbalance. Rock Auto lists single piston sets as well as full sets.

Wsa111 : Thank you for reminding me of that diagnostic tip. I did that once to test a bum cylinder in my F-250 about 15 years ago. The test indicated the exhaust valve was damaged. Pulled the head and a sizable portion of the exhaust valve was gone.

You guys have re-convinced me to re-ring all 6, assuming no block damage.

I can obviously pull the head with the engine still in the car. Being there is no belly bar, it looks like I should be able to drop the oil pan without lifting the engine. May have to drop the steering idler arm with the front wheels dangling for additional clearance. Does that sound feasible?

I haven't pulled connecting rod caps before. I suppose pulling the cap nuts will allow the cap to drop with minor persuasion (ie: plastic hammer tapping). Should I expect any struggle with this? Any wisdom on this would be appreciated.

I suppose having the journal pointing away from the camshaft for the cap break and removal, then hand crank the journal up to push the piston/rod up, followed by cranking the journal down to pull it away from the rod, leaving the piston/rod at TDC for extraction through the top of the block would be the way to go.

Or, should I just do everything at BDC with no crank turning and just hand push the piston/rod up through the block?

I'm not as worried about reassembly. Cleanliness is next to godliness, triple check your tolerances, and avoid metal to metal contact with journal and bearing surfaces, triple check your torques, leave nothing to chance. It's the disassembly of a 40+ year old assembly that worries me and the struggle that often times comes with it.

Thanks!

 

[rbohm]

8) when pulling the pistons with the engine in the car, you want to make sure each rod is at bdc. a few things to make sure of before you start pulling the pistons;

1: make sure there is no ridge at the top of the cylinders. if there is you will have to remove it ot you could damage the pistons as you try to remove them.

2: you want to go easy when tapping on the connecting rods while pushing the pistons out of the block. take care NOT to use the rod bolts as a place to hammer on if at all possible as you could loosen up the bolts.

3: after you remove the rod caps, and before you start to remove the rod/piston combination, put a couple of short lengths of vacuum hose on the rod bolts to prevent the threads from scratching the crank journal.

4: take a good look at the bearings and the journals and see how they are wearing to this point. there should be no copper showing on the bearings, and the journals should be smooth. light scratches are ok as long as you cant catch your fingernail on them.

 

[SoCar72]

Awesome. Thanks for the tips. I think I'll have a set of rod bearings just in case I find some that are overly worn.

The rod bolts are 3/8" diameter aren't they?

Thanks!

 

[rbohm]

Awesome. Thanks for the tips. I think I'll have a set of rod bearings just in case I find some that are overly worn.

The rod bolts are 3/8" diameter aren't they?

Thanks!

8) i believe the rod bolts for the small six are actually 5/16"

 

[SoCar72]

I believe you are correct on the bolt size. The rod bolts that CI lists are SBF standard bolts which are 5/16". The 351w, Boss, and Cleveland engines used 3/8".

I ordered the parts today : rings, rod bearings, oil pan gasket, head gasket, and exhaust gasket. $165 through RockAuto with shipping. Everything is Sealed Power and Fel-Pro. I may get into this later this week.

 

[wsa111]

What kind of rings did you?? Plain cast or moly.

Make sure you check the endgap on each ring in its cylinder.

If you install moly rings you better hone the cylinders with a 500 grit hone & then plateau hone the bores for a very smooth slick finish.

In your case you would be better with just plain cast rings & hone with a 380 grit dingleberry hone. Bill

 

[rbohm]

What kind of rings did you?? Plain cast or moly.

Make sure you check the endgap on each ring in its cylinder.

If you install moly rings you better hone the cylinders with a 500 grit hone & then plateau hone the bores for a very smooth slick finish.

In your case you would be better with just plain cast rings & hone with a 380 grit dingleberry hone. Bill

8) good information here.

 

[SoCar72]

I got cast iron rings, mostly per your recommendations. Everywhere I've read pretty much praises the iron rings for most every build except the high-end performance builds where limits are really being pushed.

Installation question : The top 2 ring sets are cast iron and all 12 are marked for "top". Each set of 6 iron rings has a bevel on the inside radius, one set of 6 has the bevel on the top inner radius, and the other six on the bottom inner radius. Which goes in the top groove? The included instructions are rather generic and don't clarify. I'm inclined to face the bevels away from each other, top inner bevel in the top groove. It seems to make more sense in terms of preventing ring roll on the compression and power strokes and allowing compression bleed to build behind the ring to help it blow out toward the cylinder wall for better sealing.

Bottom groove is straight forward - the expansion ring sandwiched between 2 thin rings with the gaps opposed. Clocking all of the gaps so than none line up is on the list of "watch out for's".

Motors Manual states gap clearances at 0.010 for the top 2 rings and 0.015 for the bottom cluster (with the expansion ring butting tight per Sealed Power's specs). Piston clearance should range from 0.0007 - 0.0023. Sound good to you guys?

Thanks!

 

[rbohm]

8) another bit of advice, when you hone the cylinder walls as wsa described, make sure that you CLEAN then thoroughly afterwards. you dont want all those little bits of metal screwing up your engine after doing all that work. start with lint free rags and a good cleaner like chemtool, and clean the cylinder walls until you can run a white lint free rag through the cylinders and they come out clean. also take a clean lint free rag soaked wit atf, and wipre down the cylinder walls after you are done cleaning them to prevent rusting of the cylinders while you have the engine apart. it happens faster than you think it might.