78 XS750 with excessive oil burning and lower compression in center cyl.

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Sep 25, 2024
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I purchased this bike with 21,000 miles on it. They are known for sticking rings especially in the center cylinder as it runs hotter than the outboard ones. It has always used more oil than it should and a compression check revealed the center cylinder was lower than the outboard cylinders. I have used the HPL cleaning product with little affect. I was going to get some Auto rx, but he now only sells a minimum of 2 qts. I had really good luck with it in my 6.9 diesel and it's highly regarded on the diesel forum I frequented. They had before and after compression readings which showed the increase in compression which proves it cleans the rings, but I don't need 2 qts. and he didn't even reply to my email. Project Farm had a Ford tractor that required ether to start when cold and compression was lower than it should have been. He used some Engine Restorer on it and compression readings were up and he didn't have to use ether on it any more to start it. He did a 1 yr. follow up with no change in compression or performance. I got a can of it and then found out they don't recommend it be used in wet clutches so there went that fix.
I came across a couple of videos of a guy using B-12 Chemtool on Audi 2.0 engines with very serious oil burning issues. Pours it down the plug holes and lets it sit for 8 hours and then turns the motor and gives it a second dose. Fixed both of the cars issues in miraculous fashion. I did this to the bike last fall and I can honestly say the oil smell coming from the crankcase breather is not near as noticeable or maybe even gone so blowby has been reduced. I have ridden the bike appx 100 miles and it has used 1/2 qt. of oil so oil usage hasn't really gone down.
The only difference which might affect my results are the Audi cylinders sit straight up and down and the XS cylinders are slanted towards the front so the Chemtool poured in might not be getting to the rear of the piston. I haven't checked compression again which might tell me something, but I would need to borrow the compression tester again. I adapted an XS850 oil cooler to the bike and the oil temps are much cooler now. I have a Yoshimura Multi meter so I can monitor the oil temps and high oil temps cause the stuck rings.
Trying to think of a easy way to get the cylinders straight up and down so the Chemtool can work on all parts of the rings. Should I give the Hpl a second try? I saw something to the effect that it's not proven to clean the ring area and that's the only area I need the stuff to work. I just remembered I used some of Yamahas gas additive that was supposed to clean rings, but I can't really say it did anything noticeable.
The bike now has very close to 30,000 miles on it and I thought I had this problem licked with the Chemtool, but checking the oil after the ride today I found out differently.
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How long did you run the HPL? It doesn't clean quickly, it's not designed for that. It can take several thousand miles.

What is the leakdown and compression like on that cylinder?
 
I did run it for several thousand miles, but with the amount of oil it was using I'm not sure there was much HPL left. Never done a leak down test and I'm not sure if I could find the figures from the compression test, but the center cylinder was lower than it should have been. I did that test about 7 or 8 years ago. I'm sure I kept them, just not sure where they are.

Looks like the pictures didn't work.
 
I just got the thing back together and inspected so I can ride it. I've got the manuals and have little desire to tear into the motor unless absolutely necessary. Been wondering if I could rotate the motor in the chassis to where I could get the cylinders straight up and down for better coverage with the Chemtool.
 
I just got the thing back together and inspected so I can ride it. I've got the manuals and have little desire to tear into the motor unless absolutely necessary. Been wondering if I could rotate the motor in the chassis to where I could get the cylinders straight up and down for better coverage with the Chemtool.
Take the rear wheel off.
 
Nice bike! I love the late 70s Yamaha 750s and 1100s. My dad had an XSEleven Special. Maybe if you put the front wheel up on an elevated ramp it would make the cylinders vertical?
 
I was thinking about hanging the front end higher with some tie downs to some hooks I screwed into the floor joists above. I kind of like the idea mentioned above of taking the rear wheel off and that would be more stable as it would rotate on the center stand and might just be enough to do it.
 
Anyone know how the picture thing works. They loaded, but couldn't get them to appear. Nothing but a question mark.
 
Easy for you to say. I don't think it's monkey business when people have had great results with the Chemtool and stopped their oil usage.
 
I'm a bit confused ... The OP states that he put "several thousand miles" on it, but also that he "just got the thing put back together"? Maybe there's a delay in the storyline I'm not understanding?

The HPL EC and oil need time to dissolve the ring deposits. If you've put 5-7k miles on those products and there's still a compression issue, then no other product will fix this problem; you'll need to do a ring/hone job.

As for the pix ... our website was having some system/server upgrades the last few days and it may have been affected, but it seems the photos loaded fine (I removed the duplicate photos).
 
Is the air/oil separator in place? I had a 76 and it used oil from the start, installed the A/O separator and it cut consumption and ring clogging to nothing. It had 75K miles when I sold it. The A/O separator is in the breather hose at the crankcase.
Smoky
 
Put it on the center stand, take off the rear wheel, lift the front wheel. If you need more elevation, put a board under the center stand. You should be able to get the cylinders vertical. Then do your B-12 soak.
 
I'm a bit confused ... The OP states that he put "several thousand miles" on it, but also that he "just got the thing put back together"? Maybe there's a delay in the storyline I'm not understanding?

The HPL EC and oil need time to dissolve the ring deposits. If you've put 5-7k miles on those products and there's still a compression issue, then no other product will fix this problem; you'll need to do a ring/hone job.

As for the pix ... our website was having some system/server upgrades the last few days and it may have been affected, but it seems the photos loaded fine (I removed the duplicate photos).
This has been ongoing for several years since I got the bike on the road and found the low compression and oil usage. The HPL and the Yamaha ring treatment were the first things I used. After putting the Yoshimura multi meter on and seeing the too high oil temps I bought an oil cooler setup off an 850 which wasn't just a bolt on and that is why I just got the bike back on the road, that and for some reason the headlight quit working.

Thanks for the work on the pictures, but I still don't see them.
 
Is the air/oil separator in place? I had a 76 and it used oil from the start, installed the A/O separator and it cut consumption and ring clogging to nothing. It had 75K miles when I sold it. The A/O separator is in the breather hose at the crankcase.
Smoky
The oil separator is in place, but the stock hose just has a filter on the end. When I got the bike I put pods on and got rid of the stock airbag for several reasons.
 
Put it on the center stand, take off the rear wheel, lift the front wheel. If you need more elevation, put a board under the center stand. You should be able to get the cylinders vertical. Then do your B-12 soak.
Going to try and get some riding in before it gets too cold, but this is the way I'm going to attempt the job. Thanks.
 
Have you checked the valve clearance ever in that 30,000 miles? You could be barking up the wrong tree if the clearance hasn't been checked and you have a valve not fully closing.
 
Have you checked the valve clearance ever in that 30,000 miles? You could be barking up the wrong tree if the clearance hasn't been checked and you have a valve not fully closing.
A valve not closing would cause a miss or poor running, but I don't see how it would cause oil usage. The clearances were checked before I put it on the road and it runs great although it would probably run better with the compression up to snuff.
 
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