Cam Chain O-ring Blown

[WaconiaGSer]

Hi Everyone,

I have a '79 GS850G that likes to blow it's cam chain o-ring that's at the level of the head gasket. When I bought the bike last year this was blown and it did it again about a month after I put considerable time and money getting the bike running well.

My thought is that one of the exhaust pipes is plugged and exhaust gas is getting past the piston rings, into the lower end of the engine and creating pressure that blows the o-ring. Can't find any info to verify this but after doing so much other work on it last season, don't know what else it might be.

ANY HELP/ADVISE WILL BE GREATLY APPRECIATED!

[tkent02]

Hi Everyone,

I have a '79 GS850G that likes to blow it's cam chain o-ring that's at the level of the head gasket. When I bought the bike last year this was blown and it did it again about a month after I put considerable time and money getting the bike running well.

My thought is that one of the exhaust pipes is plugged and exhaust gas is getting past the piston rings, into the lower end of the engine and creating pressure that blows the o-ring. Can't find any info to verify this but after doing so much other work on it last season, don't know what else it might be.

ANY HELP/ADVISE WILL BE GREATLY APPRECIATED!

Is your breather plugged?

[WaconiaGSer]

I dunno'. The thought hadn't occurred to me and I don't remember my mechanic mentioning it, either. Could you explain to me how this could cause my problem.

[BassCliff]

Greetings and Salutations!!

Hi Mr. WaconiaGSer,

The breather circuit is there to allow the crankcase to "breathe" so that it does not build up pressure enough to blow gaskets and seals.

There is cam chain tensioner repair information and links on my website. Let me roll out the welcome mat for you...

Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

[WaconiaGSer]

Thank you very much tkent02 & BassCliff. Just as soon as my ordered gaskets arrive I will tear into this again and check the breather. Probably is the most likely culprit by what you described. Will let you know what I find.

[tomcat24551]

...I will tear into this again and check the breather.

If you find the breather chambers on top of the valve cover are clear and the hose going from there to the top of the airbox is clear, the problem may be that the chamber in the top of the airbox is clogged.

The '79 has a metal airbox and the blow-by gasses from the crankcase are corrosive, so if your bike has had very poor maintenance for 30 years or so, that small, upper airbox chamber could be clogged with scaly rust or who knows what kind of crud. This is a worst-case scenario, but make sure this little chamber is clear and if you can treat the inside of it with some kind of anti-rust treatment (like POR-15), do so.

Tomcat

[WaconiaGSer]

Nothing has ever gone as it should with this bike!

I told you all that I'd get back to you when I had torn into the engine to take care of the blown cam chain o-ring gasket and I just got to that point.

As you all suggested I checked the breather, breather hose and even the top of the air box where the breather hose goes to. The breather and hose were very clear and, although I could not visually verify, the top of the air box seemed very clean as well (a screwdriver pushed down the connection for the tube produced absolutely no resistance).

I did find something that might be of interest and possibly give a clue. The tops of #s 1 and 4 cylinder heads were heavily covered with a layer of soft black deposits. Last year when my mechanic and myself worked on the bike it appeared that 1 and 4 might not be doing the best but we did a lot of diagnosing and work to make sure that all was well. We put in new points, set the timing and then checked the spark plugs and the charge going to each one. They were all good. Wondered if the coil for cylinders 1 and 4 could be bad but, again, the charge at all plugs was good.

Part of the work also done at that time was overhauling the carburetors and they were all functioning great. Also, the cylinder head was milled just in case it was warped at all.

So, I don't know what is up! Could the problem with cylinders 1 and 4 be as simple as old plug wires on the coils? And, could the cam chain o-ring problem be caused by cylinders 2 and 3 running well (and hot) and cylinders 1 and 4 running more cool? Could that be causing the head to warp when the engine is at operating temp and be giving the o-ring enough space for it to blow out?

I know that these are great bikes and can't help but think there has to be something that we have just missed. That when that is corrected the bike will be just fine.

Again, any help will be greatly appreciated!

[WaconiaGSer]

Nothing has ever gone as it should with this bike!

I told you all that I'd get back to you when I had torn into the engine to take care of the blown cam chain o-ring gasket and I just got to that point.

As you all suggested I checked the breather, breather hose and even the top of the air box where the breather hose goes to. The breather and hose were very clear and, although I could not visually verify, the top of the air box seemed very clean as well (a screwdriver pushed down the connection for the tube produced absolutely no resistance).

I did find something that might be of interest and possibly give a clue. The tops of #s 1 and 4 cylinder heads were heavily covered with a layer of soft black deposits. Last year when my mechanic and myself worked on the bike it appeared that 1 and 4 might not be doing the best but we did a lot of diagnosing and work to make sure that all was well. We put in new points, set the timing and then checked the spark plugs and the charge going to each one. They were all good. Wondered if the coil for cylinders 1 and 4 could be bad but, again, the charge at all plugs was good.

Part of the work also done at that time was overhauling the carburetors and they were all functioning great. Also, the cylinder head was milled just in case it was warped at all.

So, I don't know what is up! Could the problem with cylinders 1 and 4 be as simple as old plug wires on the coils? And, could the cam chain o-ring problem be caused by cylinders 2 and 3 running well (and hot) and cylinders 1 and 4 running more cool? Could that be causing the head to warp when the engine is at operating temp and be giving the o-ring enough space for it to blow out?

I know that these are great bikes and can't help but think there has to be something that we have just missed. That when that is corrected the bike will be just fine.

Again, any help will be greatly appreciated!

I have ordered new coils and think that should solve some problems. Don't know for sure, but hope that it will cure the o-ring problem, too.

[bonanzadave]

Is your breather plugged?

Check items 9 & 10. If they're all gunked up thats a plugged breather.

[WaconiaGSer]

Nope, the filters/screens are clean. I don't think that the breather is plugged at all.

Check items 9 & 10. If they're all gunked up thats a plugged breather.

[Matchless]

Just a comment, I have seen an engine with the newer MLS headgaskets, that covers the slot for the cam chain o-ring where the PO fitted the o-ring and bolted the head down. The o-ring is not to be used if the later gaskets that cover the o-ring slot is fitted and can cause sealing problems as it lifts the head gasket up.
If you use the older type gaskets then the o-ring is still to be used.

[WaconiaGSer]

That is very good information. Thank you! Is there a newer o-ring that is to be used with the new head gasket? Or should I use the good old gold silicone gasket?

Just a comment, I have seen an engine with the newer MLS headgaskets, that covers the slot for the cam chain o-ring where the PO fitted the o-ring and bolted the head down. The o-ring is not to be used if the later gaskets that cover the o-ring slot is fitted and can cause sealing problems as it lifts the head gasket up.
If you use the older type gaskets then the o-ring is still to be used.

[Matchless]

That is very good information. Thank you! Is there a newer o-ring that is to be used with the new head gasket? Or should I use the good old gold silicone gasket?

The o-ring is not supposed to be used with the later OEM spec type MLS gasket that has a smaller rectangular hole than the older type. The gasket then overlaps the o-ring head and cylinder area and performs the sealing function. The gasket usually has a layer of viton rubber and will not need silicon sealer, goes on dry. I know some who run a light smear around the opening though, not sure if its good or bad.
Whereas the older composite gaskets had a larger rectangular opening and requires the o-ring to form the seal between the cylinder and head, metal to metal.
The o-ring should not seal metal to gasket, as it is designed include the thickness of the gasket.

In actual fact if the o-ring pushing on the gasket prevents the head from seating properly compression leaks on #2 & #3 is also likely if oil leaks from that area and could even warp the head.

Let us know the outcome.