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what is SOP for fixing warn cylinder


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  #1  
Old 07-18-2006, 01:07:04 PM
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Craig DeShong Craig DeShong is offline
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Default what is SOP for fixing warn cylinder

I recently got a Briggs FH, tore it down, did a general clean-up, and got it running in short order. It’s run a few times (for about 5 min. or so each run) but it’s using oil and I’ve noticed (when it’s cantankerous and won’t start) that oil puddles on the top of the piston. The cylinder (at the top of the stroke) is oval and measures .003 thousands by .005 thousands oversize.

For you guys that get these old engines and have this problem, what is the Standard Operating Procedure to correct this? Do I need to hone the cylinder (as the Briggs book indicates) to the next size and replace the piston and rings? If so, are the parts available? Where do you get them? Or is there a less drastic solution.. like just new rings?

Thanks for your advice
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Old 07-18-2006, 01:20:55 PM
Dan Baalman Dan Baalman is offline
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Default Re: what is SOP for fixing warn cylinder

Doesn't sound like it is too worn to me. I bet the rings aren't seating in the bore. Have you honed the cylender to break the glaze? I would do that and then consider new rings. They are available from sponsors of this site.
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Old 07-18-2006, 05:41:02 PM
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Default Re: what is SOP for fixing warn cylinder

If you had the rings off the piston maybe they were re-installed upside down. A more likely source of oil getting into the cylinder is the intake valve guide or even a malfunctioning crankcase breather. The wear (.005"-.003" = .002 out of round) isn't great enough to warant a bore/ring procedure and shouldn't be enough to cause oil consumption.

Forrest A
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Old 07-18-2006, 05:58:36 PM
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Craig DeShong Craig DeShong is offline
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Default Re: what is SOP for fixing warn cylinder

I wasn't clear enough in my explination. I've had the piston out, but was very careful to make sure when I re-installed it, that I maintained it's orientation (so it's not in backwards). I did not remove the rings from the piston. They looked ok and were not "stuck" (don't really know what acceptable rings look like. I guess I could take ther piston out again and meeasure the ring clearence if it would help). I'm sure the rings have been rotated on the piston however... so they are not touching the bore as they were before disassembly, and with an oblong bore... this must be enhancing the problem.

The engine has overhead valves.. so the oil MUST be comming past the rings.

The bore is supposed to be 2.250 dia. It is 2.253 north and south and 2.255 east and west at the top of the bore. What I tried to say earlier was that I could hone the cylinder to 10 thousands over bore but then I would need to get an oversize piston and rings. I'm wondring if "things are that bad"... and you guys who have experience probably know and can advise me as how to proceed.

Thanks for your replies.
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Old 07-18-2006, 09:20:05 PM
Andrew Mackey Andrew Mackey is offline
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Exclamation Re: what is SOP for fixing warn cylinder

.005 over, with .002 differential is not too bad. The fact that the piston was removed, and the rings possibly rotated would equal a ,004 gap - enough to pump some oil. I would hone lightly, with a glaze breaker (it just takes the shiney surface off), and install a new ring set. Check the new rings for fit in the piston grooves. if they have more than .002 side clearance, perhaps a new piston is in order. If that is the case, I would go for the oversize. Is this a cast iron piston? If so, it can be flame sprayed oversize, if you cannot find a NOS one.
Andrew
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Old 07-18-2006, 09:40:34 PM
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Default Re: what is SOP for fixing warn cylinder

On the FH that I have, when I first got it and took it apart, I was shocked to find how much the rings had worn - They were down to about half the thickness of new ones. In my opinion, an FH has a rather skimpy oil supply to begin with and if you let that get low and / or dirty, you can wear parts out in a hurry. I agree with the others that your cylinder is not in too bad a shape and that a light honing to break any glaze and a new set of rings will probably be all you need.
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Old 07-19-2006, 07:59:26 PM
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Default Re: what is SOP for fixing warn cylinder

Hey Craig,
I agree with the others, it's pretty common to find oil on top of a Briggs piston. I think perhaps that has spooked you Does it smoke? How much oil is gone from the sump after a tank of gas is run? I bet it's OK in the cylinder, ring, and piston department.
LOL, Bill
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Old 07-20-2006, 08:06:00 AM
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Craig DeShong Craig DeShong is offline
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Default Re: what is SOP for fixing warn cylinder

Well, I tore it down again last night, pulled the piston out and removed the piston rings. Like I already said... don't know what good rings should look like because working in this area is new to me. The piston looks ok (to me) in that the ring seats don't appear to be excessively worn from what I can tell with a feeler gauge. The bottom two ring seats were ok but the top ring seat had a lot of crud in it... which I cleaned out. I would guess the rings are probably worn out (from all the helpful advise you guys have posted above) and because I can compress them well inside the piston, and when they are compressed to where they would be in operating condition now, there is about a 3/16 in. gap between the ring ends... which to me seems like a lot.

To answer Bill's question... I haven't got it to run for the last few days I've been fooling with it. Other folks have told me that excessive oil in the combustion chamber will keep the fuel mixture from igniting. This seems to bear out because when I mop all the oil out of the cylinder, and off the valves, and off the plug; and them re-assemble and give it a squirt of ether... it will reward me with a pop or two... but then nothing till I clean the oil out again. I've checked and re-checked the timing, and spark, and even disconnected the fuel supply just to be sure it wasn't getting flooded.

I'm going to take your advise from the above postings and get some new rings and we'll see what that does. Thanks again for your replies.
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Old 07-20-2006, 02:02:50 PM
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Default Re: what is SOP for fixing warn cylinder

Replace the rings, they can't be too expensive, but CHECK THAT BREATHER.

I recently had a Briggs engine (not and FH) that smoked quite badly, but when I tore it down, I found the bore not too bad and the rings not too bad either (but both with enough to cause me to get standard chrome rings for thr Al bore).

What caused all that smoke? When I took the breather off, it was full of oil (probably from loading and unloading the tiller it came from) meaning it was not "breathing". How does this cause oil to burn? Instead of retaining a partial vacuum in the crankcase as it should, pressure builds up in there and oil can be forced past rings that are even good, let alone ones with any wear.
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Old 07-20-2006, 07:23:43 PM
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Default Re: what is SOP for fixing warn cylinder

Hey Craig,
3/16 is quite a gap, I think about .010 would be about right for new rings, worn ones will go ten times that. Worn rings will be sharp on the top and bottom edges, but may still give good service. But rings with a 3/16 gap probably won't.
Oil in the cylinder will usually aid compression and starting to a point. If the oil wets the plug, it will not fire. Sounds like you are working things out. Good luck

Bill
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Old 07-21-2006, 01:43:24 PM
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Default Re: what is SOP for fixing warn cylinder

I agree with Bill. 3/16" =.1875 is WAY to big for the engd gap. I would be surprised if your engine can get enough compression to run like that. Even 3/32 is way to big. Install new rings and lightly hone the cylinder to rough it up a little and I bet that you will have a good runner. Make sure that you install the rings correctly. The package usually has a picture showing how they are supposed to fit onto the piston.
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Old 08-23-2006, 11:20:32 AM
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Thumbs up Re: what is SOP for fixing worn cylinder

Since I received so much encouragement and information from so many folks I thought this thread needed a conclusion. I ordered and received the rings from Otto, installed them, and it started on (practically) the first attempt. Thanks to all of you that responded for your guidance and encouragement!
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