80k on a 2002 Monster 750... rebuild or get a new 750?

[Jordan1234]

Hello!

I just bought my first motorcycle - a 2002 Monster 750.  It was $700.

The guy I got it from said it had a "blown head gasket" which I've since learned is only half true since the 750 has o-rings.

My question is this:
With 80k on the motor is it worth trying to fix, or should I just get a new(ish) motor on ebay?

More detail:
From research, at best I'm looking at a head gasket and valve job.  At worst the cylinders are worn and there is so much blowby that the engine needs a total rebuild, at which point a new motor is more cost effective.  I've got lots of experience fixing/rebuilding automobile engines and a good set of tools so I'm not intimidated by the work, but if the community can tell me before I even start that 80k miles is too much then I'd love to save myself the trouble.

Thanks!!!
-Jordan

[koko64]

For the cost of repairs you could pick up a cheap 900 motor and fit it yourself.

[cokey]

damn i need to find a bike for 700$..  and i second that.. if you can, might as well put in a bigger motor..

[Howie]

Or properly diagnose the problem.  Start with a compression test, or better yet, a cylinder leakage test.  I remember a friend of mine buying an air cooled VW with a "bad engine".  A new distributor cap fixed that one.

[koko64]

Or properly diagnose the problem.  Start with a compression test, or better yet, a cylinder leakage test.  I remember a friend of mine buying an air cooled VW with a "bad engine".  A new distributor cap fixed that one.

True. Check it all out first, if the motors shagged get a 900, if not and its a simple fix, fix it and ride. Sometimes people miss simple stuff and you get a bargain.

[Jordan1234]

To do a compression test (or leakage test) I'm still looking at replacing the cylinder-head orings and dedicating a few hours... but it sounds like its possible that the motor could be fine other than that.

My big concern was that 80k is way outside the design spec for these engines; i.e. its unheard-of for a 750 to still have decent compression past 80k miles.  It sounds like this is not the case.

Thanks!

[greenmonster]

Nicasil cyl walls last longer than 80k.
But if it still got original pistons, the rings surely will be worn, and maybe guide seals.
Leak/comp test is good.

[Jordan1234]

Ok... I should also go ahead and get the cylinders honed and put new rings in while its apart, and the nikasil coating should be fine - i.e. the cylinder walls havent ground out too much.

20 minutes of internet research showed me that new rings cost ~$150 per piston, which is crazy.  Am I missing something?  I just rebuilt a 6.4L FE and the premium rings were $40 for all 8 cylinders.  Is there a secret place in the internet that doesnt charge an insane amount for a little piece of metal?

[greenmonster]

20 minutes of internet research showed me that new rings cost ~$150 per piston, which is crazy.  Am I missing something?

No, they are expensive.

The positive side is that an uppgrade to Hicomp pistons will cost just a little more than rings. 

[akmnstr]

I'd let the compression test be your guide.  As I recall, a stock 750 should be around 140 psi when new.  It is an easy job to pull the head but you will need to either make of buy a special tool to remove and replace the head nuts.  You could have your bike fixed in a few hours. 

[2-Skinny]

Not going to touch the 900 swap suggestion...? 

[evoasis]

Swap out with a lower miles engine, it's pretty easy if you get the same year/ CC size...  GL!

[Jordan1234]

Will a 2001 M750 motor fit on my 2002 M750 frame?

EDIT:
Thanks for the advice everyone - I did a compression test and have 90 PSI on the horizontal and 0 PSI (?!) on the vertical.  A bit of exploration demonstrated that the vertical timing belt was broken, and the cam on the vertical cylinder wont turn by hand.  90 PSI is much lower than 140 so I suspect that I've got significant blow-by.

There is a 2001 M750 engine on Ebay that I'll buy if it fits - that would save me a great deal of time and possible even money.

Thanks!
-Jordan