Compression and Engine Question

[visionrevisit]

I had my 1982 Vision looked at by the mechanic and he said my compression is 128psi
or so.  He recommends me sell it and get nother one.  Should I look for an engine
swap of just buy another bike? I have a lot of money in this one and would prefer
to keep it.    He does not recommend a bore and hone.  Can I get another engine
and swap or should I give up?  I don'y want to start over unless a get a newer
bike like a BMW ot Buell or Yamaha

visionrevisit

Daniel Nordeen

[Brian Moffet]

My front cylinder was 119, and the rear 121 when I checked them December 3, 2006.  In my case, it's a 25 year old bike, with 42000 miles or more on it.  It's going to have low compression because of age.  However, it runs fine, and doesn't have any problems because of it.  I wouldn't want to race a modern bike with it, but for a daily commuter it's fine.

I would be more interested in whether there is any major difference in the pressures.  How long has the bike sat without running?  On the Visions, rarely do people need to replace the pistons and rings.  A few have changed out the bottom end.  I've changed neither.  I expect my bike to last at least another 20,000 miles or so, at least as far as the top-end is concerned.

Oh yes, in an airplane, a cylinder is considered bad only after it loses 25 percent or more of it's compression.  In my airplane, that would be a decrease from 100 psi to 75 psi...  On the vision, I think that would drop your compression to around 110.

Brian

[Lucky]

yes, definitely, gone! (the mechanic that is)

[inanecathode]

In an airplane, if you sneeze on it the right way you have to rebuild the engine  :D

128psi is fine revisit, your mechanic doesnt know much about motorcycles, and seeing as the vision isnt just a motorcycle that could be problematic in the future.

[Walt_M.]

Sounds like a mechanic at a dealership. Some are there not to fix bikes but to sell new bikes.

[YellowJacket!]

Or even worse, the next thing out of your mechanics mouth would be "I'll give you $175.00 for it" as he looks away and grins to himself......

David

[Rick G]

128 is fine. If it was down to 100 I'd worry. I've used the same top end on the last two bottom ends ( had a valve job in '05 ) and it runs fine. Didn't even bother to check compression , there nothing i could do about it anyway.
Many of todays mechanics were trained by MMI and are full of theory , but don't really know anything.

[inanecathode]

128 is fine. If it was down to 100 I'd worry. I've used the same top end on the last two bottom ends ( had a valve job in '05 ) and it runs fine. Didn't even bother to check compression , there nothing i could do about it anyway.
Many of todays mechanics were trained by MMI and are full of theory , but don't really know anything.

Theres a certain level of "good enough" you learn from crazy uncles/fathers and shade treeing in general :)
They dont teach you that canned air is a freeze spray if you turn it upside down in mmi, but try telling a graduate of that school to shrink a bearing race without a refridgerator/freezer :P