Blowing a little too much smoke.

[Sibbo]

Tilly, my R80 ST is using a bit too much oil, it's not a huge problem but I'm slowly working myself up to doing a rebuild .

Am I going to be able to get away wit just rings or is a set of bearing required too?

[ME 109]

If you're in there Sibbo, it would be wise to at least inspect the big end bearings. And as the cost of the bearings is reasonable, it would be unwise not to replace them anyway.
Just need to know which size bearings to get.

[Kurt in S.A.]

I'm currently doing a top end on my /7 at 100K miles...just about everyone I've asked is saying leave the bottom end bearings (shells??) alone. At most, I might stick a feeler gage at the bottom and see what thickness it takes to eliminate the movement.

If you're smoking, it's likely the top end anyway. Have you done a compression check? Better yet, do a leakdown test to see where the air escapes to. Simple tests...does it smoke when you get on the gas? Probably rings. Does it smoke when you chop the throttle coming down a hill? Probably guides.

At 100K, I'm doing it so that I can change out the old valves/seats to the new style.

Kurt in S.A.

[Major Softie]

I think knowing the mileage on your bottom end is a vital detail in making such a recommendation.

If it's the motor's first top-end job, I doubt it will need any bottom end attention, but it's still always a good idea to check it. If this bottom end has 250k miles on it, well that would be very different.

[georgesgiralt]

Hello !
I would take the equation by the dollar end.
If you only work on the valve and rings, you need *also* new base barrel gaskets, head gasket, and rubbers for the push rods.
And of course, rings and/or valves...
Plus the time to work on it.
So imagine you do not change the rod main bearing, and in a few hundred miles you had to open it up again.... You wasted all these gaskets and your time, both of which are not cheap...
The cost difference is a set of bearings and the 4 bolts for the rods... And you gain peace of mind which is priceless...
Compare with the price of 2 head gaskets, 2 base barrel gaskets plus the little o-rings on the oil tube, and the 4 rubber push-rods....
Just my 2 cents...

[montmil]

You didn't mention the mileage on the bike. Helpful info. If there's less than 100,000 miles and the R80 has been cared for, the lower end should carry on without issue.

[Sibbo]

Thanks all, yep I forgot that vital stat. 127000 km or 80,000 miles . I think the top end has been worked on not too many years ago by a PO as it is twin plugged.

At least the clock shows 127000 ! .

[Sibbo]

I'm currently doing a top end on my /7 at 100K miles...just about everyone I've asked is saying leave the bottom end bearings (shells??) alone. At most, I might stick a feeler gage at the bottom and see what thickness it takes to eliminate the movement.

If you're smoking, it's likely the top end anyway. Have you done a compression check? Better yet, do a leakdown test to see where the air escapes to. Simple tests...does it smoke when you get on the gas? Probably rings. Does it smoke when you chop the throttle coming down a hill? Probably guides.

At 100K, I'm doing it so that I can change out the old valves/seats to the new style.

Kurt in S.A.

OK, a compression test sounds like a good idea .