Worn Piston Rings

Omar Morales

Omar Morales

Junior Member
Unfortunately, I am seeing more symptoms of worn piston rings with the most recent being evidence of blow by. The previous owner did mention that she would need a ring job sooner rather than later.

I plan on adding some Lucas Heavy Duty oil hoping this gets me through the season and working on a fix during the winter.

What are some risks of continuing to operate in the current condition?

I have zero idea (other than YouTube University) of how involved replacing piston rings would be. Is it possible to provide some insight?

I do enjoy working on my car but the thought of replacing the rings myself is intimidating. I imagine other components should get replaced in the process.

Depending on the complexity, I am also considering doing an engine swap with one from Schwalms (I know the cost is high).

She generally runs really smooth with no other issues other than the one mentioned above.

Any guidance will be appreciated.
 

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There is no risk to continuing to operate an engine that needs new rings. The only risk is if there are other worn parts such as bearings.

A ring and valve job was common in the early days. You will have to remove the head and pan. Removing the rod caps will allow the pistons to be removed at the top of the block. That is if there is not a ridge at the top of the cylinder. If you can feel a ridge with your finger nail then a ridge reamer will be required.

Mark everything so that it goes back together exactly as it was.

While you are in there check for rod bearing wear. If you can move the rod up and down at all on the crankshaft the bearing will have to be adjusted by taking one or more shims out. Also check the valves. Turn the engine over to open the valves one at a time to see if there is excessive wear on the valve face and/or seat. The shinny surfaces of the valves and seats should be uniform all around.

Working on the Model A engine is not hard and there is no reason to be intimidated. Have a friend who has had experience with automotive engines help. Study up on engine overhaul techniques by reading a book or on the internet before you start the job.
 
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You will have to pull the cylinder head and oil pan at the minimum to re-ring the pistons. You might as well change the pan's front donut seal while you're at it. So, plan on ordering these parts besides the rings.
And since we are discussing piston rings, do not trust what is stamped into the pistons for size when ordering new rings. If the engine has a lot of wear, chances are the new rings will not fit properly and have a wider end gap than spec's call for. I am dealing with this very problem in an extremely worn engine in a Model A owned by a local specialty car business. The stamped piston size reads 0.080". So, we ordered that size rings. When they arrived, I test fitted the top ring a couple inches from the block's deck. Instead of the recommended 0.014"-0.016" end gap, the new ring gap was about 0.026+"! That's unacceptable. Grumbling between my teeth, I ordered the next size bigger rings at 0.100", hoping the gap would close up enough to be used as is if the cylinders were that worn. Nope. 0.026" measured end gap minus 0.020" (the difference between 0.100" and 0.080 bore) = 0.006", as even the New Math would tell us. Now the problem was reversed = the end gap was too close! The only way to save the situation short of a complete engine rebuild was to HAND FILE each of the 0.100" rings in order to achieve the desired 0.016" end gap. That means four top rings, four 2nd groove rings and eight oil groove rings (one on top and one below the scraper) = 16 rings hand-filed. It didn't take as long as I thought to do this, maybe an hour, including test fitting and measuring. Now all 16 rings are 0.016" end gap and should seal well. I know it would have been better to pull the engine, bore out the cylinders and install new pistons and rings. But this is a budget "rebuild", so the path we chose should work.
A long story to answer your question about re-ringing pistons. I just wanted to prepare you for a shock if the cylinders are worn beyond what the piston stampings tell you they are. Measure your old rings first (as I should have done!) in each cylinder to get an idea of how much wear there is. That will dictate which size piston rings you order.
By the way, since you'll have the oil pan down anyway, this will give you a perfect opportunity to adjust the rod bearing clearance, as "nkaminar" recommends. Shoot for 0.0015". If your rings are that badly worn, then the rods most likely need attention, too.
Marshall
 
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nkaminar said:
There is no risk to continuing to operate an engine that needs new rings. The only risk is if there are other worn parts such as bearings.

A ring and valve job was common in the early days. You will have to remove the head and pan. Removing the rod caps will allow the pistons to be removed at the top of the block. That is if there is not a ridge at the top of the cylinder. If you can feel a ridge with your finger nail then a ridge reamer will be required.

Mark everything so that it goes back together exactly as it was.

While you are in there check for rod bearing wear. If you can move the rod up and down at all on the crankshaft the bearing will have to be adjusted by taking one or more shims out. Also check the valves. Turn the engine over to open the valves one at a time to see if there is excessive wear on the valve face and/or seat. The shinny surfaces of the valves and seats should be uniform all around.

Working on the Model A engine is not hard and there is no reason to be intimidated. Have a friend who has had experience with automotive engines help. Study up on engine overhaul techniques by reading a book or on the internet before you start the job.
Click to expand...

Thank you so much for the guidance!!
 
Marshall V. Daut said:
You will have to pull the cylinder head and oil pan at the minimum to re-ring the pistons. You might as well change the pan's front donut seal while you're at it. So, plan on ordering these parts besides the rings.
And since we are discussing piston rings, do not trust what is stamped into the pistons for size when ordering new rings. If the engine has a lot of wear, chances are the new rings will not fit properly and have a wider end gap than spec's call for. I am dealing with this very problem in an extremely worn engine in a Model A owned by a local specialty car business. The stamped piston size reads 0.080". So, we ordered that size rings. When they arrived, I test fitted the top ring a couple inches from the block's deck. Instead of the recommended 0.014"-0.016" end gap, the new ring gap was about 0.026+"! That's unacceptable. Grumbling between my teeth, I ordered the next size bigger rings at 0.100", hoping the gap would close up enough to be used as is if the cylinders were that worn. Nope. 0.026" measured end gap minus 0.020" (the difference between 0.100" and 0.080 bore) = 0.006", as even the New Math would tell us. Now the problem was reversed = the end gap was too close! The only way to save the situation short of a complete engine rebuild was to HAND FILE each of the 0.100" rings in order to achieve the desired 0/016" end gap. That means four top rings, four 2nd groove rings and eight oil groove rings (one on top and one below the scraper) = 16 rings hand-filed. It didn't take as long as I thought to do this, maybe an hour, including test fitting and measuring. Now all 16 rings are 0.016" end gap and should seal well. I know it would have been better to pull the engine, bore out the cylinders and install new pistons and rings. But this is a budget "rebuild", so the path we chose should work.
A long story to answer your question about re-ringing pistons. I just wanted to prepare you for a shock if the cylinders are worn beyond what the piston stampings tell you they are. Measure your old rings first (as I should have done!) in each cylinder to get an idea of how much wear there is. That will dictate which size piston rings you order.
By the way, since you'll have the oil pan down anyway, this will give you a perfect opportunity to adjust the rod bearing clearance, as "nkaminar" recommends. Shoot for 0.0015". If your rings are that badly worn, then the rods most likely need attention, too.
Marshall
Click to expand...

Thank you so much for the guidance!
 
As I admitted, the cylinders in the engine I'm trying to bring back from the dead really should be bored out and the next larger pistons installed. They are worn way beyond what an engine should still use. But, this is not only a budget rebuild; it's also an experiment to see if my procedure will work.
The rest of what I wrote in my SHORT answer still applies to your project. Check the old ring gap before ordering your new rings! By the way, should you need a new set of 0.080" rings, I'll sell the ones we blindly ordered last week for half the catalog price plus postage. :) My mistake, my loss...
Marshall
 
Marshall, I have a piston ring grinder which works great and was quite inexpensive. I’m afraid that at the moment I am unable to send a picture but I think you can find it at Summit or Speedway without much trouble. It sounds like it might be a handy tool for you to have on hand.
 
Thank you, jeepguy1948. I hope I don't have to do this procedure again. I'll look up the tool you recommend, but it would have to be darned cheap to beat the $10.00 mill file price I paid specifically for this job. :)
M.
 
In worn bores, ring end gaps should also be measured at the bottom of travel and set to minimum spec there. If set to original spec just below the top in a worn bore, the rings may end butt at the bottom of travel with dire consequences.
 
I pushed the rings not quite halfway down the cylinders, using an upturned piston to square them before measuring end gaps. This is where most of the wear in the cylinders will occur. Your advice is good, but in this particular case, the engine is so worn throughout that I'd be surprised if the bore diameter at the bottom of the cylinders is even close to being too tight. With an end gap of 0.016", the taper would have to be really drastic to cause the ring ends to butt against each other. However, as the new rings are on the still-uninstalled pistons, tomorrow for grins and giggles, I'll remove a couple random rings and check their gaps further down in the cylinders. I'll report back what I find for discrepancy between mid-bore and bottom-bore ring end gaps.
Marshall
 
Omar, take this as free advice from a Model-A rebuilder. You are likely wasting your time re-ringing an engine. If the rings are worn because of mileage, then the bores are likely worn excessively as will be the skirt of the pistons. Re-ringing usually entails honing the walls (enlarging the bore even more) where the rings can conform to the shape of the cylinder walls. The issue is that each bore will likely be worn out-of-round too, so getting the new rings to seal against those worn walls is going to be difficult at best. You may already have a better seal with what you have. ;)

The next issue you likely will encounter is the skirt of the piston will be worn allowing the piston to 'rock' within the bore. When this happens, the faces of the rings do not travel parallel or co-planer with the cylinder wall while moving vertically up/down the cylinder wall. This wears a beveled angle on the corners of the compression rings which soon acts as a funnel allowing compression to leak into the ring land, ...which is also likely worn. Many old mechanics used to have worn pistons knurled. Also, they installed an oversized ring and filed to fit the end gap. There were wornout vehicles back then and they were trying to get another 500-1000 miles before it would be scrapped. Hopefully that is not your intent!!

So, in essence what you are about to do is spend a lot of effort and a few hundred dollars for a gasket set, a set of rings, some freight and some oil ...all to find out you aren't much better off than when you started.
 
Omar I agree with Brent. Based on your limited comments relative to your experience with engine rebuilding and more specifically the Model A going with a professionally rebuilt engine is a wise direction. You live in NJ and not too far away from Schwams. You can save some shipping cost by transporting it yourself. The most involved part of this process will be removing and replacing the engines. Good success.
 
Good advice, Brent. The voice of experience speaks. Based upon what Omar has read here and other research he may have made, he just needs to decide whether he wants a patched-up job to get a few more miles out of the car while he saves up bigger money for the full engine rebuild we suspect he needs, or bite the bullet now and send the engine off for a stem to stern rebuild. It'll never be cheaper than now to rebuild a Model A engine in the coming years as Babbitt-pouring guys pass from the scene.
So, patch up or rebuild? There's room in the Model A world for both ways to go. So many factors to take into consideration when making this decision, both financial and practical. Pro's and con's for each way could be grist for a new thread. Boy-howdy, will the staunch opinions come out of the woodwork in THAT thread!
Marshall
 
Rebuilding is a bunch of money, but the peace of mind and confidence to drive the car afterwards is worth a lot.
 
nkaminar said:
A ring and valve job was common in the early days. You will have to remove the head and pan. Removing the rod caps will allow the pistons to be removed at the top of the block. That is if there is not a ridge at the top of the cylinder. If you can feel a ridge with your finger nail then a ridge reamer will be required.

Ditto

The cylinders should also be honed out before re-installing the pistons w/new rings.

The ring end gap should be measured after honing, near the bottom of travel as that's where the least cylinder wear is.
Piston rings are generally made of cast iron, so if the ends need to be filed down to increase the gap it's not hard to do.

If one removes a little too much while filing the end of a piston ring to increase the end gap, it's no big deal, nothing to worry about.
Click to expand...
 
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"I'll remove a couple random rings and check their gaps further down in the cylinders. I'll report back what I find for discrepancy between mid-bore and bottom-bore ring end gaps."

I checked a couple new 0.100" rings, whose end gaps I opened up with a file, in the lower regions of the cylinders. There was no major difference in end gap from where I had measured it up higher in the cylinder. I won't have to worry about the ring end gap closing up and seizing when the pistons are down in their bores. That's a relief!
Marshall
 
Marshall V. Daut said:
I checked a couple new 0.100" rings, whose end gaps I opened up with a file, in the lower regions of the cylinders. There was no major difference in end gap from where I had measured it up higher in the cylinder.
Marshall
Click to expand...

That tells me that there's very little wear in the cylinder.:)
 
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