Question on 80 hp 4 stroke

[case man]

I'm looking at a 2000 model 80 hp that has the head off.The dealer said that it had low eratic compression after the owner dedicided to ajust the valves himself.My question is how much side to side clearance should the pistons have? Just guessing but they appear to have .008" or so. It seems like alot to me,but I'm new to the 4 stroke outboards. There is no cylinder ridge at the top,and appears to have very little wear in the cyclinders. I can buy motor,controls,and everything for $800. The shop owner does not like 4 strokes at all,and is telling me that the 2 strokes will equal or better the 4 stroke in fuel economy. What do you guy's think?

 

[rodbolt]

Re: Question on 80 hp 4 stroke

I think the dealer is a shadetree.
however on the F80, depends on why the compression was low/eratic. why wasnt there a leakdown test run?
just be aware that the F80 can be very expensive to put back together.
there is just no way a two stroke, unless its DFI can equal a 4 stroke in fuel econiomy.
the 2 stroke burns fuel everytime the piston comes up and the 4 stroke everyother time.

 

[case man]

Re: Question on 80 hp 4 stroke

Is .008" to much clearance between the piston? If this was a old Chev. motor I would replace the pistons. Also is there someplace I can go to check the spec's for clearance's and bore dia.? Is this a very dependable engine? I know ,too many questions. If I can get this engine running strong and still only have about $3000 in it,is that to much? Case Man

 

[rodbolt]

Re: Question on 80 hp 4 stroke

dunno, thyere is no spec on the piston crown area.
only way to test it, in both a yamaha and a chevy, is to either remove the rings and use a feeler guage or to measure the piston skirt and bore then do the math.
no other way.
the valve clearence can be checked and adjusted with the head on the bench. do that, then using a new gasket bolt the head on and correctly install the timing belt, then do a leak down test to see whats damaged if anything.
most all of it is in the service manual and marine technical guide.
but like most overhead cam desighns the valve lash can be be checked and adjusted with the head on the bench.
most any decent motorcycle shop can rebuild that head .

 

[case man]

Re: Question on 80 hp 4 stroke

Thanks Rodbolt for the info,I'll run by the Yamaha shop and get some spec's on the motor today.If your ever in OKlahoma,the coffee is on me.