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Ram Jet 01-04-2009 12:17 AM

Piston Ring End Gap
 
I need a-little advice. I've written enya-engine.com twice and didn't get my usual immediate response from Ken Enya. I just bought and rebuilt an Enya .46-4C. The ring endgap is .011" or .279mm. It seems excessive to me. Any guesses as to what is acceptable? In addition, does anyone know the where abouts of a gentleman that specializes in piston ring sales and, I think, manufacture that is mentioned many times in posts here.

Thanks,
Bill

w8ye 01-04-2009 12:58 AM

RE: Piston Ring End Gap
 
ringmaster46@msn.com
Frank C. Bowman
1211 N Allen Ave.
Farmington, NM 87401
505 327 0696

I was thinking .004" per 1" of bore but this only comes up about once a year and I forget

".004 inches times the bore diameter for the top piston compression ring"

Charley 01-04-2009 01:01 AM

RE: Piston Ring End Gap
 

Quote:

ORIGINAL: Ram Jet

I need a-little advice. I've written enya-engine.com twice and didn't get my usual immediate response from Ken Enya. I just bought and rebuilt an Enya .46-4C. The ring endgap is .011" or .279mm. It seems excessive to me. Any guesses as to what is acceptable? In addition, does anyone know the where abouts of a gentleman that specializes in piston ring sales and, I think, manufacture that is mentioned many times in posts here.

Thanks,
Bill
Is it a pinned ring? If so, deduct the diameter of the pin.

CR

DarZeelon 01-04-2009 01:57 AM

RE: Piston Ring End Gap
 
1 Attachment(s)

Quote:

ORIGINAL: Charley


Quote:

ORIGINAL: Ram Jet

I need a-little advice. I've written enya-engine.com twice and didn't get my usual immediate response from Ken Enya. I just bought and rebuilt an Enya .46-4C. The ring endgap is .011" or .279mm. It seems excessive to me. Any guesses as to what is acceptable? In addition, does anyone know the where abouts of a gentleman that specializes in piston ring sales and, I think, manufacture that is mentioned many times in posts here.

Thanks,
Bill
Is it a pinned ring? If so, deduct the diameter of the pin.

Wrong, Charley!

The pin does not protrude fully through the ring...
The ring ends can touch each other, over, under, or outside the ring...

The first photo is from Wiki, shows a pin protruding into the upper part of the middle ring.

The other two from Tower show the OS ring, which closes over (outside) the pin and the Super Tigre ring, which has the pin 'cavity' completely outside the ring-gap...



As to the actual gap, Bill; Jim is right and it should be about 4 thousands per inch of piston diameter.

With the Enya .46 having a bore of under 1", the ring you have should have a gap of about .004".
So yes, it does seem excessive.


Talk with Frank Bowman. He's very helpful; even on the phone.


w8ye 01-04-2009 02:06 AM

RE: Piston Ring End Gap
 
Yes and get your new ring from Frank.

He makes the best ones for model glow and gas engines

Ram Jet 01-04-2009 02:11 AM

RE: Piston Ring End Gap
 
Nope Charley, it's not pinned. But good advice anyway. Thanks.

Bill

Ram Jet 01-04-2009 02:55 AM

RE: Piston Ring End Gap
 
Thanks w8ye. I will order from Frank. I'm guessing that this little Enya has either had a-lot of use or was run very lean on oil. Surprisingly the main bearings are in good shape but they will survive on very little oil anyway. The engine makes a click when the toe of the cam approaches the follower and another click on the tappets ride down the backside of the lobe. I suspect loose manufacturing gear lash to be the culprit as spur gears seldom, if ever, wear out. I'm hoping the loose gear lash will be of little importance when the engine is running at speed.

Thanks again,
Bill

w8ye 01-04-2009 02:56 AM

RE: Piston Ring End Gap
 
The clicking is normal

asmund 01-04-2009 03:05 AM

RE: Piston Ring End Gap
 
All my fourstrokes from the cheap ones to my YS click, A friends brand new YS 63 clicks too. Quite normal, if there wasn`t a clicking sound from the cam followers/tappets then I would suspect them to be stuck and need maintainance;)

Ram Jet 01-04-2009 03:21 AM

RE: Piston Ring End Gap
 
Thany you asmund. I'm new to four cycle model engines. I would be quite concerned if a full scale engine of mine made noises like that.

Regards,
Bill

Ram Jet 01-04-2009 03:28 AM

RE: Piston Ring End Gap
 
I'm releaved. I should have posted weeks ago then I wouldn't have been sitting here fretting about it. I was disappointed that Enya didn't install the little brass wrist pin retainers like they did on my .19 and the brass thread insert for the glow plug threads. I was happy to see that the valve seats were cut into brass inserts in the head. I'll give you a tip. Work on the valve springs, retainers and retainer clips inside a cardboard box. I lost one of the itty bitty retainer clips in the carpet and spent two hours looking for it.

Thank you.
Bill

Motorboy 01-04-2009 04:16 AM

RE: Piston Ring End Gap
 
Quote:

ORIGINAL: DarZeelon

As to the actual gap, Bill; Jim is right and it should be about 4 thousands per inch of piston diameter.

With the Enya .46 having a bore of under 1", the ring you have should have a gap of about .004".
So yes, it does seem excessive.

This ring gap are for 2 stroke engine. The 4 stroke engine has a bit larger ring gap to allow the oil to enter into the crankcase for the moving parts need oil..

Ramjet told about his engine are the Enya 46-4C, this is a 4 stroke engine.

Ramjet..

Are your engine running well at idle and start easy each time, nice trottling? If the engine works well without problem, replace the ring not neccesary.

My Magnum XL 52 FS has ring gap at 0.03 mm and works well as it will be.

wjvail 01-04-2009 08:34 AM

RE: Piston Ring End Gap
 
Every OS and Saito I've measured is .010". Big ones little ones, old one new ones... all about the same. As Motorboy said, it's how they lube the lower end. It is why we are able to run these engines on 10% oil and why 4C engine need less oil in general. All the major moving parts are lubricated not by a mixture of methanol and oil, but by mostly undiluted oil.

Since I mix my own fuel, there is also a lesson here... and that is, it is dangerous to assume that fuel and operating procedures for one type of engine will work for all engines. While fuel for an OS with .010" ring end gap may be fine with only 8 or 10 % oil, the next engine may be a Laser with .002" and need not only more oil in the fuel, but periodic supplemental oiling under the valve cover. What is good for the goose is not always good for the gander.

Bill

gkamysz 01-04-2009 08:41 AM

RE: Piston Ring End Gap
 
While rebuilding a magnum .91 RFS I measured ring gap at .012", 0.3mm and checked one of my OS FS-91 to find it was .006", 0.15mm as one would expect per the .004"/1" bore rule. I have a new ring for the Magnum but haven't checked to see what the gap is.

Ram Jet 01-04-2009 08:59 AM

RE: Piston Ring End Gap
 
It's nice to know i'm not alone Greg. A call to Frank Bowman in your future?

Regards,
Bill

Ram Jet 01-04-2009 09:18 AM

RE: Piston Ring End Gap
 
Yes, I agree. Fuel/oil/nitro combo requirements for each engine are as varied as prop diameter and pitch. Most of us just don't bother to experiment. I'll be interested in Frank Bowman's view on this end gap issue. Honda recommends an end gap of .0118 on my 500cc 4 cycle single. If the .004"/1" piston diameter guideline were applied .014" would be acceptable. At .0197 honda specifies replacement. It looks like Honda leans toward .0035/inch. Interesting.

Bill

Motorboy 01-04-2009 10:10 AM

RE: Piston Ring End Gap
 

Quote:

ORIGINAL: Ram Jet

Yes, I agree. Fuel/oil/nitro combo requirements for each engine are as varied as prop diameter and pitch. Most of us just don't bother to experiment. I'll be interested in Frank Bowman's view on this end gap issue. Honda recommends an end gap of .0118 on my 500cc 4 cycle single. If the .004"/1" piston diameter guideline were applied .014" would be acceptable. At .0197 honda specifies replacement. It looks like Honda leans toward .0035/inch. Interesting.

Bill
4 stroke model engine and 4 stroke engine with oil in the pan are the ring gap not the same. We should not have larger ring gap in the 4 stroke engine with its own oil lubrication system in that oil consumption will not increase and in addition there is an oil scrape ring that keeps the oil away from the combustion space.

For small ring gap leads to the ring expands and running tight in the cylinder. For a large ring gap leads to compression loss. Right gap size in the upper and lower limits in the ring gap for 4 stroke engine model is not easy to measure. The engine are running without problems and it comes enough oil out of the crankcase means the ring gap are in the "right sized gap"

gkamysz 01-04-2009 10:20 AM

RE: Piston Ring End Gap
 
I don't think ring gap is all that critical. Some texts say it might be worth a couple percent in power, but there are so many other things that influence power in our models engines that the ring gap is the last thing we need to worry about.

Ram Jet 01-04-2009 10:21 AM

RE: Piston Ring End Gap
 
Thanks Greg.

Bill

Ram Jet 01-04-2009 11:18 AM

RE: Piston Ring End Gap
 
I don't think it matters whether an engine has a wet sump oil system, a dry sump oil system or whether the oil is mixed with the fuel. Ring end gap is important for proper combustion and overall efficiency of an engine and may even be more citical in a two cycle in that ring blowby will contaminate the incoming fuel/air charge. In an ideal world there should be zero end gap in an engine that has reached proper operating temperature but that state is nearly impossible to achieve and may be undesireable in an overheated engine. Ring end gap is quite easy to measure. Place the ring in the bore and square it in the bore with the piston crown. To get real fussy and check for cylinder taper it should be measured in position at the top of the stroke and the bottom. Simply use a good quality set of feeler gages and use the old "go/no go" method of obtaining a very accurate end gap measurement.

Well, that's what I think.

Regards,
Bill

Ram Jet 01-04-2009 11:21 AM

RE: Piston Ring End Gap
 
That might be to say that compression ratio is not important and that ring blow by and the resultant contamination of the incoming fuel/air charge in a two cycle is of little consequence.

Regards,
Bill

Motorboy 01-04-2009 12:03 PM

RE: Piston Ring End Gap
 

Quote:

ORIGINAL: Ram Jet

Ring end gap is quite easy to measure. Place the ring in the bore and square it in the bore with the piston crown. To get real fussy and check for cylinder taper it should be measured in position at the top of the stroke and the bottom. Simply use a good quality set of feeler gages and use the old "go/no go" method of obtaining a very accurate end gap measurement.

Well, that's what I think.

Regards,
Bill
Yes, in bigger engine, not so simple in model engines. The ring gap can be smaller than the feeler will go into.. The test are to run the model engine are in good contidion or not as i wrote in early post: Are your engine running well at idle and start easy each time, nice trottling? If the engine works well without problem, replace the ring not neccesary.

Most critical ring gap are in 2 stroke engine since the cylinder filling are bad. The 4 stroke engine has much better cylinder filling hence the ring gap are not critical.

gkamysz 01-04-2009 12:07 PM

RE: Piston Ring End Gap
 
Ring blow by amount is very small when ring sealing is good regardless of the ring gap. The bigger the gap the more power loss, and this may be exaggerated in model size engine because the gap relative to the cylinder volume is large. If it bothers you replace it. I hope to actually investigate this but I have no idea how I would do a controlled experiment for something like that. I just checked some new parts for the Magnum 61 four stroke and measured .003" and the bore is just under 1". I also checked an Enya 46-4C with low time at .004".

Like Jens says, unless the engine is not running correctly I wouldn't bother. It is after all a model engine.

Ram Jet 01-04-2009 12:45 PM

RE: Piston Ring End Gap
 
Your point is very well taken. I guess the only definitive way to check the affect of end gap on compression would be to fashion a pressure guage connected to reinforced rubber tubing with a drilled out glow plug internally threaded to accept a tire valve stem valve.

Oh heck, I think I'll just call Frank Bowman.[sm=idea.gif]

Regards,
Bill

Ram Jet 01-04-2009 12:50 PM

RE: Piston Ring End Gap
 
Yes, and as my friend's father would say "If it ain't broke, don't fix it." I just can't resist tinkering. Maybe if I did less tinkering I could fly more often.[sm=thumbs_up.gif]

Cheers,

Bill


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