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1981 Honda CX500
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Discussion Starter · #1 ·
Hey all,

I want to try some MMO especially in the right cylinder which I note is not as strong as the left. Granted, the bike only has like 100 miles since rebuild after sitting (and laying down) for several years. When I got the bike which was laying on its side for a few years, I did find some junk in the right cylinder which cleaned off pretty easily. No idea what it was but it was some hard caked on stuff. It did not seem like rust though but almost like the stock head gasket material. I wish I kept the crud to check on what it was. It cleaned off pretty well / left no marks. Anyways, these days the bike usually starts right up even when cold and is in decent shape overall.

I do want to try some MMO in the cylinders through the spark plug holes as I have read about on this forum. According to the MMO's website "Marvel Mystery Oil is not recommended for use in motorcycles with wet clutches."

Obviously, I will not be pouring it per their recommended 80% regular oil and 20% MMO suggested mix but just adding some through the spark plug hole and then I guess pulling any excess out. Even if some of the MMO got into the oil, it would be like what 2%? Is that something people should be worried about with the MMO getting into the engine oil and possibly mixing in and getting on the wet clutch?
 

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Before adding MMO a little more investigation is warranted. Have you run a compression check or a leak down test since the rebuild? What was involved in the rebuild?
 

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1981 Honda CX500
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Discussion Starter · #3 ·
Basic quadruple bypass. I cleaned up the right cylinder with piston not removed. i regret not trying to get a foot look of the piston on right side. i just cleaned the top of the pistons and any / all carbon from valves etc for everything up to he head gadgets but not beyond the head gaskets.

compression left side average about 125.

Right side average about 85.

leak down test not completed.

my hunch oxidation or rust on right piston ring. this is because last owner left bike on its side outside in michigan. any rain or melted snow over the years infiltrated to piston. top of right piston might have had a different color to its metal. i have photos somewhere.

what could it hurt though to let the mmo soak a few days as i won’t plan to do any intensive work like piston rings until the winter?
 

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Was the bike burning oil after the rebuild?
 

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Discussion Starter · #5 ·
I never tried to start it before the rebuild. after the rebuild when i first tried to start it, it would be have been the first time in 7 or more years that the thing ran. i mean the exhaust was not clear at first but all that cleared up after warming up.

There were things burning out of there but I wouldn’t say it burned oil.

Why do you ask that?
 

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When these engines sit for a while the rings can get stuck. If it shows no evidence of burning oil then the oil control rings are probably OK. The rings often free up after a few hundred miles of use. I'd suggest to just ride the bike a bit more before trying the MMO.
 

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Discussion Starter · #8 ·
When these engines sit for a while the rings can get stuck. If it shows no evidence of burning oil then the oil control rings are probably OK. The rings often free up after a few hundred miles of use. I'd suggest to just ride the bike a bit more before trying the MMO.
Okay. Thank you for the suggestion. I will try that.
 

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Discussion Starter · #9 ·
What do you think the MMO will cure or accomplish?

What do you expect after using the MMO?
Since the bike sat for so long (under some unconventional storage circumstances), I am assuming the rings could be stuck and was curious to see if the MMO could help speed up the process of loosening up the rings a bit. As reclinedrelic suggested, maybe putting on a few hundred miles might do the trick without MMO.

I guess I could plan to also check compression every hundred miles to see if there is any change. Of course, it could be one of those things where there is no gradual improvement and one day / one ride it just breaks loose finally.

Again, I was hoping the MMO might be a good idea for a few days of soaking to see if it could help break things loose a bit.
 

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Discussion Starter · #10 ·
FYI

On the right cylinder which has the lower compression number, the compression does improve right away if I pour a bit of oil into the right cylinder through spark plug hole.
 

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@Stingmaster 75. In post #1 you indicated the bike has 100+/- miles since rebuild. In post #10, you indicate the compression rises with a wet compression test.

This wet compression test indicates the piston rings are not functioning well. With the bikes history, I suspect corrosion has gotten to the sealing edges of the piston rings.

I seriously doubt if MMO will cure the issue, I believe you may need a replacement set of rings for that cylinder.

On the other hand, a trial with MMO won't hurt, although, it may not help. Temper your expectations from the MMO.

Can you peak inside the cylinder with a bore scope to possibly inspect the condition of the cylinder wall?

Good Luck resolving the low compression.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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As MMO is touted as an oil treatment, there should be no problem if some gets into the crankcase. Unless I'm mistaken, it's full of detergents rather than fiction modifiers.
If you suspect a problem, you can change the oil.
 

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Discussion Starter · #13 ·
@Stingmaster 75. In post #1 you indicated the bike has 100+/- miles since rebuild. In post #10, you indicate the compression rises with a wet compression test.

This wet compression test indicates the piston rings are not functioning well. With the bikes history, I suspect corrosion has gotten to the sealing edges of the piston rings.

I seriously doubt if MMO will cure the issue, I believe you may need a replacement set of rings for that cylinder.

On the other hand, a trial with MMO won't hurt, although, it may not help. Temper your expectations from the MMO.

Can you peak inside the cylinder with a bore scope to possibly inspect the condition of the cylinder wall?

Good Luck resolving the low compression.
Ty for the data.

Yea, I looked more at MMO as an option and do not think it will be a cure all. It contains agents that could help remove carbon build up and could help prevent rust, with the keyword being prevent rust (not remove rust). Prevention of course is not the same as removal. Maybe it would help to remove any carbon or sludge deposits which could have an effect on breaking up some corrosion over or under any carbon. At the same time, I could have it sitting for a week with MMO soaking or I could just replace the rings over a weekend and be done with it.

When I had the head removed, the top half of the cylinder wall with the piston pushed all the down looked just fine. There was slight discoloration of the wall at one spot but it still looked still smooth and had a shine to it.
 

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Discussion Starter · #15 ·

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Discussion Starter · #16 ·
Sorry one more question if anyone can offer their advice.

Right now I am assuming it might be possible to do the piston ring job on the right side only without dropping the engine. I believe it may still be a pain but possible for the right side only to do it with engine still mounted.

I have not taken the front cover off yet and have not touched anything in there. What else should I possibly look at replacing while I am in the front? Clutch is okay.
 

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Sorry one more question if anyone can offer their advice.

Right now I am assuming it might be possible to do the piston ring job on the right side only without dropping the engine. I believe it may still be a pain but possible for the right side only to do it with engine still mounted.

I have not taken the front cover off yet and have not touched anything in there. What else should I possibly look at replacing while I am in the front? Clutch is okay.
Sorry one more question if anyone can offer their advice.

Right now I am assuming it might be possible to do the piston ring job on the right side only without dropping the engine. I believe it may still be a pain but possible for the right side only to do it with engine still mounted.

I have not taken the front cover off yet and have not touched anything in there. What else should I possibly look at replacing while I am in the front? Clutch is okay.
Download a copy of the factory service manual. The oil pump has to be removed to gain access to the right side big end. A good time to replace the oil pump chain and to check the internals of the oil pump.
 
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You might be giving up too soon on getting the rings free. Have you soaked the mmo in that cylinder yet? After the soaking you should take it for a hard ride for at least an hour but I recommend a good solid day of riding. If there is a mountain pass near you that would be good to go up too. Ride it like you stole it, these motors are happier that way even when in perfect condition.
 

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Discussion Starter · #19 ·
You might be giving up too soon on getting the rings free. Have you soaked the mmo in that cylinder yet? After the soaking you should take it for a hard ride for at least an hour but I recommend a good solid day of riding. If there is a mountain pass near you that would be good to go up too. Ride it like you stole it, these motors are happier that way even when in perfect condition.
Maybe you are right. It is supposed to rain for 3 or 4 days. I might go ahead and try MMO. At worst (or at best) the MMO may help loosen things up a bit.

If I have corrosion in there causing the piston ring to stick, could it hurt if I poured a bit of MMO through spark plug hole and some type of penetrating catalyst / oil like a PB Blaster? In other words, what if I created a mixture of MMO and a good penetrating oil and poured that mix in and let it soak? I feel like it would just be like MMO plus additional compounds that are in the penetrating oil that are more proven to help loosen up corrosion.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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I'd plan on an oil change if you do try that. I don't think it would have any long term effects if you don't run it with the thinned oil.
 
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