How many miles is the bottom end good for?

[scott s]

I have a '78 engine with a LOT of miles on it; almost 80,000. It runs fine, but has low compression. I figure it's needs a re-bore/rings, valve job, etc.

But what about the bottom end? No known issues, just LOTS of miles. If I wanted to put this engine back in service, what, if anything, would you tend to on the bottom end?

 

[bloodthirstysystem]

bearings, clutch, repair the hole in your sump filter

 

[xjwmx]

Do you have any idea what's been done to the motor before? The low compression implies to me the whole motor has lasted 80,000, because the first thing somebody would address would be rings. Of course the rings could have been done before, but my motor has 25,000 and compression is like new.

I'm asking to find out how long motors last...

 

[scott s]

bearings, clutch, repair the hole in your sump filter

It has new clutch plates and the filter has been replaced.

 

[650Skull]

Would depend on how the motor has been ridden and serviced. The only way to tell would be to pull the top end for a re-bore and check the tolerances on the little end and any play in the big end and bearings. 85,000 is a lot so when you do the tear down check the size of the pistons, (oversize), and that will give you an indication how many times it has been rebuilt. Some mechanics don't like to do a 1st oversize, .25, they go straight to the second .50

 

[scott s]

Well, I'm just figuring on everything from the case UP needs attention. I was wondering about the bottom end....the transmission, bearings, etc.

The motor has been well cared for with minor things repaired along the way.

 

[XSLeo]

As 650Skull says you wont really know till you get in there.
I rebuilt a crank just recently, all new bearings and Heavy duty rods About $480 in parts.
I would tear it down and check things out. If the runout on the crank is ok and the rods check out good then just the top end needs doing. $400-$500 in parts and a few days she'll be up and running just fine. A bit of careful shopping can knock that back a couple hundred.