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Do I have the wrong rings?

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Basil

Basil

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I had my Spit 1500 engine rebuilt a few years ago, but have only put about 2000 miles on it since, so I don't think what I am seeing is due to excessive wear. At the time, I bought after market flat top pistons and had them installed by a machine shop (I assumed they knew what they were doing). Anyway, I have my motor torn down now and on a stand. Before reinstalling the now cleaned up pistons into the bores (I just lightly hones them) I decided it would be a good idea to check the ring gap. So, I took the top ring off a piston and inserted it about 3" down the bore, per the manual. The gap is supposed to be between .015 and .038 (not sure why such a wide variance?). Anyway, at 3" down the bore, the gap is about .065" which seems way too much! Now the question is, were my bores bored out too big, or do I have the wrong rings or possible the wrong size pistons/rings for the bore? It has been awhile, but I seem to recall I was putting in .030" oversized pistons, which leads be to wonder IF:

Is it possible that the bore was bored out .030 over, but the pisons/rings I received were actually standard diameter? Might that account for the fact that the ring gap seems to be about .030 or more TOO large?


This is going to be fun, I can just tell!

Basil
 
Something is obviously wrong.

You need to measure the bores and see what they actually are.

Meanwhile (in case you don't have an ID micrometer or bore gauge handy), it would be interesting to see if the ring gap is the same at top, middle and bottom. Should be the same, top to bottom.
 
It appears to be the same gap (or very close) at both the top and the bottom (by bottom, I mean about 3" down the bore, which is where the book calls for measuring "bottom." The bores seem to measure just about exact as standard bore size (2.9") so it doesn't appear they are oversized bores. Could it just be the rings are worn that much? The measurements given in the book (.015 to .038) are for if you are fitting NEW rings. These have a few thousand miles, but really not much more than that. It it possible though that I'm just seeing normal ring wear? Seems a bit excessive given the relatively few miles on the motor. If I had 50k on it I could believe that. What do you think?
 
I don't think it is wear. For that to happen, with no cylinder wear, you would have needed to wear off almost .010 on the rings. Pretty hard to imagine.

I vote poor quality control and mechanic who did not check it prior to installation. Or, someone read the clearance wrong and ground off some of the ring (long shot).
 
Are these new rings? New or old, have you tried a few more rings to see if that is about average or just that ring? At any rate, the gap is too big.
 
TR6oldtimer said:
I don't think it is wear. For that to happen, with no cylinder wear, you would have needed to wear off almost .010 on the rings. Pretty hard to imagine.

I vote poor quality control and mechanic who did not check it prior to installation. Or, someone read the clearance wrong and ground off some of the ring (long shot).
Click to expand...

Agreed.

I re-ringed my 1500 Spridget four years ago and the ring gap has hardly changed over that time. It never uses oil.
And that's probably 5000 miles of <span style="text-decoration: underline">racing</span>.
 
Basil, from what I've been told over the years, the point might be moot. Even having rehoned the cylinders, I suspect you'd be better off renewing the rings. And from personal experience, I'd consider getting a good set of rings and sending them off to Total Seal for the "gapless" modification they do. I used their converted rings (Grant cast iron rings purchased from TRF)in an 1147cc Spitfire ex-race car and was extremely happy with the results.
 
FWIW, Steve Hedke at British Pacific has been talking about this very thing lately. He claims to have seen it in quite a few different engines (including Triumphs, old Land Rovers and even an old Ford flathead V8). Basically it's extreme ring wear in just a few thousand miles on freshly rebuilt engines. Maybe Bob M. can chime in, as I believe it was his TR4 that triggered the discussion. I don't recall the numbers now, but it showed huge ring gaps after just something like 4000 miles. And only the rings, for some reason.

Anyway, Steve's theory is that it's caused by the ethanol being added to our gasoline now; and feels the solution is to use Marvel Mystery Oil in the gasoline at the recommended rate (which ISTR is something like 4 oz per 10 gallons).

Also, a standard ring in a .030" over bore will have a gap that is more like .090" too large (assuming it follows the walls). Bores are measured along the diameter, while rings are along the circumference.
 
So perhaps I should order a new set of rings (standard) and see how they gap out? Any recommendations on where to get a good set of rings, and does teh fact that I have after-market pistons (flat top) matter?
 
Basil,

Can you get your hands on a cylinder bore gauge and accurately measure the cylinders before reassembling the engine? I don't doubt what Randall stated, but think that it would be a good idea to know for sure what you have in each cylinder starting out.

I'd be willing to bet that someone removed too much material creating a larger ring gap, in the event that the ethanol didn't do it.

I'd try Greg at BPNW for the AE or Deves ring set. And get the Payen gasket set as well.
 
I wonder if I could rent a cyl bore gauge? I rented the Hone from Autozone for $20 fully refundable.
 
Possibly even at some NAPA stores as well. If not, do you know anyone who works at or owns an automotive machine shop?
 
If the cylinders are worn from the rings running on them, then they would only be worn where the rings touch. That leaves several inches at the bottom, and a fraction of an inch at the top, that would be unworn. Should be easy enough to push the rings to those areas and check the gap; no need for a gauge.

Generally the wear is most severe right at the top of where the rings run (since that's where the force on the rings from combustion gases is greatest, plus lubrication is minimum), so the ridge at the top of the cylinder is a good indicator of cylinder wear. No ridge means no wear.
 
TR3driver said:
If the cylinders are worn from the rings running on them, then they would only be worn where the rings touch. That leaves several inches at the bottom, and a fraction of an inch at the top, that would be unworn. Should be easy enough to push the rings to those areas and check the gap; no need for a gauge.

Generally the wear is most severe right at the top of where the rings run (since that's where the force on the rings from combustion gases is greatest, plus lubrication is minimum), so the ridge at the top of the cylinder is a good indicator of cylinder wear. No ridge means no wear.
Click to expand...

I already checked the gap (see first post). And I don't seem to have a ridge either. But the gap is too big and I don't know why. I want to see the diameter of the bores so when I buy new rings I can be sure to get the correct size.
 
On a related question - if my ring gaps are too wide (and they seem to be), could that cause excessive blow-by into the crank and thus account for the strange oil leak I've had since having the engine rebuilt? When I shut the motor off, I would get a few seconds of oil coming out the back in a stream....just a few secs after shutoff, then it stops.
 
Heart warming to see you're building and posting, Basil. Very glad
to see and hear this. Best wishes,
 
Basil said:
On a related question - if my ring gaps are too wide (and they seem to be), could that cause excessive blow-by into the crank
Click to expand...
Oh yeah.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:] and thus account for the strange oil leak I've had since having the engine rebuilt? When I shut the motor off, I would get a few seconds of oil coming out the back in a stream....just a few secs after shutoff, then it stops. [/QUOTE]Never heard of that (but I never claimed to be a Spitfire expert). But sure, if the crankcase vent system can't keep up with the blowby and the crankcase gets pressurized, it could blow oil out almost anywhere.
 
Hi,if you carefully clean the top of the piston you should find stamped or engraved STD +30 +60 or whatever the pistons are.could be that they are the wrong sized pistons or it could be that the rings have been set at that gap.There is a good guide on "united engine and machine co"site to piston to wall gaps and ring gaps -makes interesting reading.
PS.I was always taught that if you pulled the pistons and honed the cylinders you should put new rings in anyway hence the importance of knowing what oversize the piston is to order the right rings
 
I don't know the situation. However, if the engine is still together, why not go to Harbor Freight and get an inexpensive Cylinder leak down tester and put this issue to rest? Also, if you didn't bore the engine, just honed the worn cylinders, from experience, you most likely have to much ring gap, or are at the limit of end gap, which means, after the rings seat, you will have to much gap. The only rings that I have seen lately that have the correct gap, assuming you have the correct bore, are AE. The rest of the manufactures rings I have had, and checked, are all over the place. Deves required filing, and, they insisted that I should use far less gap than stated in the TR6 manual. Also, some of their rings had to much gap, not even close, however, they did offer to replace them. I packaged them up and sent them back. AE parts are by far the highest quality parts available for LBC's. The parts suppliers want to sell parts that they make the highest margin off, not the best parts. Engine crankcae ventilation is usually designed to allow mostly fumes to escape, I don't know anything about a spit.
 
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