How To Check Piston Rings

bmw633 · 12-12-2012, 01:06 PM

Hi,

I have an 2001 GZ250 with 10K miles, and the engine suddenly has lost power. I pulled the head and everything looked ok to me, no broken rings, the valves appear ok. Carbon buildup on top of piston, which I assume is typical.

I cleaned everything and reinstalled the rings, and I used the old head gasket and torqued it down, according to specs. It started ok, but still doesn't have good power, only topping out at 45mph. I set the crank at TDC and then lined the cam according to the marks. It sounded different when I started it, like maybe I am off a link of cam chain. Is there a way to check engine timing without disassembling the engine?

The cylinder walls looked ok to me. The shop I took the bike to compression tested the engine and it only had 110 psi compression before I tore the engine down. I took the head, cam, and cylinder to a machine shop and he kinda looked stupid, said he didn't work on things like that.

How do you know the rings need replacing? Should I just buy the 0.5 or 1 oversize rings, and maybe hone the cylinder walls and put it back together?

Seth Anderson
Moon, VA

mrlmd1 · 12-12-2012, 02:05 PM

Did you check the valve clearances before you took apart the engine?

**jonathan180iq** · 12-12-2012, 03:58 PM

First, I wouldn't have reused the old gasket. That's a simple and cheap replacement that's just better to go ahead and get rid of for piece of mind and to eliminate variables. Maybe there is a weak spot in it and you're getting the same results because of it.

Before the other work, did you check the basics, like checking the exhaust gaskets for leaks? Those are known to deteriorate and people have expressed similar symptoms and it was something as simple as that. I'm not insulting your intelligence. Just making sure it's all been done.

You do definitely need to get the head checked to make sure it's planed. With everything else being sound and/or replaced, a slightly warped head caused by overheating or whatever will still be losing compression...

Like with the gasket, a set of replacement rings are cheap enough, if for nothing else to know that those aren't the cause of your problem. Do you have one of those ring tester things? I don't even know what they are called but they test the tension and make sure they aren't worn

mrlmd1 · 12-12-2012, 06:02 PM

If any of the exhaust or head gaskets were leaking, you might hear a poof or see some smoke coming out where it shouldn't, but if a valve is leaking, which is more likely, if they were neglected, you could lose compression that way. The valves appearing OK don't give you the clearances, you can't see that that well.

DAN · 12-16-2012, 11:54 AM

If you have compression, spark, and gas, next check the air filter for restrictions (mega dust, ants, mouse, bee's), then check the exhaust for carbon build up at the inward exhaust pipe or it is possible the internal baffels in the muffler have rusted and collapsed causing a retriction. Personally I would do a complete cleaning of the carburator first and look at the spark timing to make sure the timing setting point has not slipped. --dan--

bmw633 · 12-16-2012, 03:16 PM

I am taking the heads, the piston, the cylinder, and the camshaft to a machine shop for them to do a valve job and to hone out the cylinder wall or bore it out, whichever it needs. I will get the rings depending on what is needed.

While I was putting the bike back together, one of the screws that holds the plastic top of the carb was loose. I am sure that impacted the bike's lack of power.

The gasket between the case and the cylinder jug: do I order another gasket or can I use some Permatex like what is used to seal the head cover?

bmw633 · 12-16-2012, 03:23 PM

Another problem I had was lining up the crankshaft and camshaft. With everything in position as per the manual, one of the two bolt holes to the camshaft sprocket is obscured by the side of the cylinder, so I had to advance the motor to the point that I could access the bolt hole. I believe on the first attempt at reassembly I did not take out the slack on the front side of the camshaft, which made the camshaft timing one link retarded. As far as bolting the the sprocket to the camshaft, is there a trick to it?

OldNTired · 12-16-2012, 11:56 PM

Quote:

Originally Posted by bmw633

I am taking the heads, the piston, the cylinder, and the camshaft to a machine shop for them to do a valve job and to hone out the cylinder wall or bore it out, whichever it needs. I will get the rings depending on what is needed.

While I was putting the bike back together, one of the screws that holds the plastic top of the carb was loose. I am sure that impacted the bike's lack of power.

The gasket between the case and the cylinder jug: do I order another gasket or can I use some Permatex like what is used to seal the head cover?

Get the gasket. Any pressure going past the rings will blow out the Permatex.

bmw633 · 12-17-2012, 12:48 AM

I am referring to the head gasket, but the gasket between the cylinder and the crank case. It is black and paper thin.

Water Warrior 2 · 12-17-2012, 02:18 AM

It would be best to go with a gasket (in my opinion) whether it be the head gasket or base gasket between the cylinder and cases.

12-12-2012, 01:06 PM	#1
bmw633 Junior Member Join Date: Aug 2012 Location: Moon, VA Posts: 20	How To Check Piston Rings Hi, I have an 2001 GZ250 with 10K miles, and the engine suddenly has lost power. I pulled the head and everything looked ok to me, no broken rings, the valves appear ok. Carbon buildup on top of piston, which I assume is typical. I cleaned everything and reinstalled the rings, and I used the old head gasket and torqued it down, according to specs. It started ok, but still doesn't have good power, only topping out at 45mph. I set the crank at TDC and then lined the cam according to the marks. It sounded different when I started it, like maybe I am off a link of cam chain. Is there a way to check engine timing without disassembling the engine? The cylinder walls looked ok to me. The shop I took the bike to compression tested the engine and it only had 110 psi compression before I tore the engine down. I took the head, cam, and cylinder to a machine shop and he kinda looked stupid, said he didn't work on things like that. How do you know the rings need replacing? Should I just buy the 0.5 or 1 oversize rings, and maybe hone the cylinder walls and put it back together? Seth Anderson Moon, VA Login or Register to Remove Ads
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12-12-2012, 02:05 PM	#2
mrlmd1 Senior Member Join Date: Jan 2008 Location: Crawfordville, Florida Posts: 2,853	Re: How To Check Piston Rings Did you check the valve clearances before you took apart the engine?
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12-12-2012, 03:58 PM	#3
jonathan180iq Super Moderator Join Date: Jan 2007 Location: Dalton, GA Posts: 3,996	Re: How To Check Piston Rings First, I wouldn't have reused the old gasket. That's a simple and cheap replacement that's just better to go ahead and get rid of for piece of mind and to eliminate variables. Maybe there is a weak spot in it and you're getting the same results because of it. Before the other work, did you check the basics, like checking the exhaust gaskets for leaks? Those are known to deteriorate and people have expressed similar symptoms and it was something as simple as that. I'm not insulting your intelligence. Just making sure it's all been done. You do definitely need to get the head checked to make sure it's planed. With everything else being sound and/or replaced, a slightly warped head caused by overheating or whatever will still be losing compression... Like with the gasket, a set of replacement rings are cheap enough, if for nothing else to know that those aren't the cause of your problem. Do you have one of those ring tester things? I don't even know what they are called but they test the tension and make sure they aren't worn Login or Register to Remove Ads
	0

12-12-2012, 06:02 PM	#4
mrlmd1 Senior Member Join Date: Jan 2008 Location: Crawfordville, Florida Posts: 2,853	Re: How To Check Piston Rings If any of the exhaust or head gaskets were leaking, you might hear a poof or see some smoke coming out where it shouldn't, but if a valve is leaking, which is more likely, if they were neglected, you could lose compression that way. The valves appearing OK don't give you the clearances, you can't see that that well.
	0

12-16-2012, 11:54 AM	#5
DAN Junior Member Join Date: Apr 2007 Location: Fort Lauderdale Posts: 25	Re: How To Check Piston Rings If you have compression, spark, and gas, next check the air filter for restrictions (mega dust, ants, mouse, bee's), then check the exhaust for carbon build up at the inward exhaust pipe or it is possible the internal baffels in the muffler have rusted and collapsed causing a retriction. Personally I would do a complete cleaning of the carburator first and look at the spark timing to make sure the timing setting point has not slipped. --dan-- __________________ 1999 GZ250 - teal green past bikes 100cc twin yamaha-1960's era - first bike 100cc and 125cc honda CB 350cc yamaha twin - 1970 160cc honda -1966 model 350cc honda CB 1970 350cc honda SL 650 Yamaha 1972 F650gs BMW 2007 Virago 750 Yamaha 1996 Login or Register to Remove Ads
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12-16-2012, 03:16 PM	#6
bmw633 Junior Member Join Date: Aug 2012 Location: Moon, VA Posts: 20	Re: How To Check Piston Rings I am taking the heads, the piston, the cylinder, and the camshaft to a machine shop for them to do a valve job and to hone out the cylinder wall or bore it out, whichever it needs. I will get the rings depending on what is needed. While I was putting the bike back together, one of the screws that holds the plastic top of the carb was loose. I am sure that impacted the bike's lack of power. The gasket between the case and the cylinder jug: do I order another gasket or can I use some Permatex like what is used to seal the head cover?
	0

12-16-2012, 03:23 PM	#7
bmw633 Junior Member Join Date: Aug 2012 Location: Moon, VA Posts: 20	Re: How To Check Piston Rings Another problem I had was lining up the crankshaft and camshaft. With everything in position as per the manual, one of the two bolt holes to the camshaft sprocket is obscured by the side of the cylinder, so I had to advance the motor to the point that I could access the bolt hole. I believe on the first attempt at reassembly I did not take out the slack on the front side of the camshaft, which made the camshaft timing one link retarded. As far as bolting the the sprocket to the camshaft, is there a trick to it?
	0

12-17-2012, 12:48 AM	#9
bmw633 Junior Member Join Date: Aug 2012 Location: Moon, VA Posts: 20	Re: How To Check Piston Rings I am referring to the head gasket, but the gasket between the cylinder and the crank case. It is black and paper thin.
	0

12-17-2012, 02:18 AM	#10
Water Warrior 2 Senior Member Join Date: Dec 2006 Location: Squamish B.C Canada Posts: 11,409	Re: How To Check Piston Rings It would be best to go with a gasket (in my opinion) whether it be the head gasket or base gasket between the cylinder and cases.
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