1996 ST1100 High crankcase pressure

Jaymillikan

Joined
Apr 10, 2024
Messages
2
Age
54
Location
Massachusetts
Hi all!

Just purchased a 1996 ST1100 non-ABS bike. In amazing shape with one small problem. Run it for a minute or two and it pushes oil out of the right valve cover. I removed the cover, cleaned it, sealed it, and replaced. Ran again, similar results.

I have been looking everywhere for a clear diagram showing the crankcase vent hoses. The emergency fuel bypass has been done, but the hose to the airbox is also missing.

Any help is greatly appreciated!
 
The Honda factory service manual has a page showing that. I don't have one anymore, but there may be someone who could post the image here.
 
Welcome from Northumberland, England.
US bikes can have a different breather configuration to UK bikes but I think they all end up pushing it into the air cleaner through the secondary air filter at the front of the air cleaner box. The filter can be replaced with a lawn mower type gauze if missing or blocked. If you follow these two pipes back you'll be able to trace the breather route.
A compression test would show if there may be an issue, although I doubt you have.
Good luck.
Upt.
 
Bush said:
The Honda factory service manual has a page showing that. I don't have one anymore, but there may be someone who could post the image here.
Click to expand...

I looked at that diagram but it is not the best as far as routing. From what I understand, it routes from the water pump and under the carbs. I'm guessing I'll have to dig deep and check it out LOL. Thank you for the info, I'll double check to make sure I don't miss anything.

Upt' North said:
Welcome from Northumberland, England.
US bikes can have a different breather configuration to UK bikes but I think they all end up pushing it into the air cleaner through the secondary air filter at the front of the air cleaner box. The filter can be replaced with a lawn mower type gauze if missing or blocked. If you follow these two pipes back you'll be able to trace the breather route.
A compression test would show if there may be an issue, although I doubt you have.
Good luck.
Upt.
Click to expand...

Thanks! I checked the compression, everything looked good. I am going to take off the tupperware and take a closer look. The emergency fuel bypass has been done, so maybe there has been some other work done prior to my purchase. Thank you for the info!

Uncle Phil said:
Check your oil level - it can be caused by overfilling the crankcase.
Inspection window at the bottom right side.
Click to expand...

I thought I had overfilled the oil! I did an oil change, and filled it to the upper line. I had oil come out of the plug well drain on the right side. I removed the valve cover, resealed the gasket, and replaced the cover. Started it again and blew out a half moon. I noticed when the engine was running the oil level dropped to the lower line. I'll double check today when I'm checking the breather hose. Thanks!
 
Jaymillikan said:
I thought I had overfilled the oil! I did an oil change, and filled it to the upper line. I had oil come out of the plug well drain on the right side. I removed the valve cover, resealed the gasket, and replaced the cover. Started it again and blew out a half moon. I noticed when the engine was running the oil level dropped to the lower line. I'll double check today when I'm checking the breather hose. Thanks!
Click to expand...
Probably isn't related but I always liked checking the oil after it stood overnight, I kept it on the top line and all was good.
 
Jaymillikan said:
I thought I had overfilled the oil! I did an oil change, and filled it to the upper line. I had oil come out of the plug well drain on the right side. I removed the valve cover, resealed the gasket, and replaced the cover. Started it again and blew out a half moon. I noticed when the engine was running the oil level dropped to the lower line. I'll double check today when I'm checking the breather hose. Thanks!
Click to expand...
Should be slightly less than 4 quarts - assuming you changed the filter.
 
I tried taking out the PCV out of my valve cover on my Mustang when I was in High School, You are entirely correct to go after the crankcase venting syste\m. I was amazed at how much oil can come out of a valve cover. Put it back in and problem went away.
 
The crankcase breather is blocked causing pressure buildup in the crankcase. It has to go somewhere so it blows by the valve cover seal.

One possibility is that someone has blocked the oil drain passage in the head between the valves with a rag or sumsuch to keep errant valve shims from falling down into the sump during a valve clearance adjustment and forgot to remove it (yes, it’s been done and reported here and on [edit: ST-Riders.orgnet]).

There have been a number of cases during a carb assembly R&R where during reassembly the crankcase breather hose was hooked up to the float bowls’ drain tube instead of the underside of the air cleaner housing. As that’s a closed system the crankcase can’t vent and blows the valve cover seals.

Or the hose is blocked somewhere else between the water pump housing and the air cleaner.

Please let us know what you find.

John
 
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PS Begs the burning question: who sold you this ST in this condition? Private party? God forbid, a dealer?? Please enlighten us with the details… please.

John (Very curious long-time ST-Rider)
 
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