low compression

[slmon92]

hey everyone,
I'm trying to get my (first) bike on the road. its an 82 heritage special. For the sake of getting it there faster, I took it to the mechanic to diagnosis the issues and repair them if it was cheap enough. he called me back today and told me I had low compression and even some rust in the cylinders. he mentioned a "cold soak" where Id simply fill the cylinders with something to take the rust off, and potentially improve the compression

REAL QUESTION:

1) has anyone done/seen/heard of such a situation and technic?
2) if I went the route of putting new cylinders in, what size and where would one find them

laugh at me, or cry with me...but then tell me what you think

 

[DARKMIDKNIGHTWARRIOR]

Did they tell you what the comp. numbers where?

 

[slmon92]

approx. 90 psi

 

[Specdog]

About 5 years ago I had the same situation with an XS360 I had just bought for cheap. I had about 90 lbs on one cylinder. I brewed up a concoction of ATF and acetone (equal parts, about one ounce each) with a spoonful of Sea Foam. I poured it into the plug hole and left for about a month. You may not need to leave it in that long, but I had lots of other things to do on the XS. It worked. The compression came up to 127 and later after I rode it for a bit, moved up to 135. I am guessing the problem was a stuck/rusted piston ring.

 

[slmon92]

interesting. has anyone else experienced such success? in my pessimistic fashion, I have begun (so far not very successfully) finding and pricing new pistons and gaskets. thanks specdog....food for thought

 

[16VGTIDave]

I'll second ATF and Acetone in a 1:1 mix. Makes every other penetrating lube look like muddy water. Pour a couple oz into each cylinder and let it sit for a day or 2 while you work on other things. Then turn the engine over by hand (a lot!) with the plugs out to try to get most of it out. Have a spare set of spark plugs handy as it may foul the plugs when you try to start it. And it will make LOTS of smoke when the engine does start.

 

[Lou Ranger]

I'll second ATF and Acetone in a 1:1 mix. Makes every other penetrating lube look like muddy water ...

I am intrigued.
Recently I tried to resurect a bicycle which had been unused for several years. Several links of the chain - the ones around the small wheel on the derailleur/changer - had seized.
WD 40 was handiest, hardly any difference
Then Gunk penetrating oil - barely any difference
Then PB Blaster - I could get them to barely move using 2 sets of big vice-grips

I knew I couldn't sit there all day wiggling 6 or 8 links until they were free enough to bend both ways around the rear changer. Didn't think of acetone and ATF.
But I did pour a cap-full of my wife's white vinegar on the links, waited about 10 seconds, rinsed it off with water and the links were 100% free. Dried it off, put on a little chain lube, good as new

Now, I am not advocating dumping vinegar into the cylinders (... although ... ), but I am recounting this to illustrate that some these expensive products are not what they are cracked up to be.
I suppose, for a bolt rusted into a thick piece of metal, that vinegar wouldn't penetrate like Blaster, but none of those expensive concoctions could hold a candle to of vinegar on that bike chain!

 

[slmon92]

16VGTIDave, you suggest I start the engine at the end of all this with the atf/acetone concoction in it ??

 

[16VGTIDave]

Only after you have spun the engine over many times by hand with the plugs out. This should get most of it either out the spark plug holes, or into the exhaust. Just be sure to not have the cylinders full or the engine will hydraulically lock and things will break!

 

[slmon92]

since I have such low compression, its not unrealistic to think that there may be holes in the rings correct? do you suggest I take the oil out before hand in case the mixture makes its way down to the crankcase?

 

[xschris]

Have the valves been adjusted yet? Was the test done dry or wet?

 

[Lou Ranger]

While it could end up being the worst case scenario with the only fix a rebuild or replacement, why not assume your mechanic could be right and you will be as fortunate as Specdog and be able to get the compression up from 90 to 135? No need to lose sleep or dollars unless and until you determine that the simple stuff isn't enough.

While you are waiting for the witches brew to do it's thing though, by all means you should take the opportunity to adjust the valves to spec and maybe ensure the gas tank is sediment free, install an in-line filter, etc.

It sounds to me like it would be a good idea to change the oil before you do any riding after it is fixed, but, subject to being corrected by a real expert, if it were me, I would leave the oil in so I could at least run it long enough to warm and mix it up before draining it out to change it.