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Head rebuild: what to replace

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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Bike: 1980 GS850G w/ 82k miles.

Prelude: Went for a 400 mile ride on the f*ing freeway in 90+ degree weather. RPMs were between 5-7k nearly the entire way. Nearly halfway through the ride I noticed a little oil on my boot. Got nervous, pulled over, but couldn't see anything leaking and my oil level was still dead-on. 200 miles in I stopped for an hour and had lunch. When I started riding again there was no oil leakage, but at about 350 miles I fould oil on my boot again, but the oil level was still good. I started to get nervous at this point, but I finished the ride and parked my bike at home.

There were a few drips of oil under the bike in the morning, but I rode it to work without any trouble, other than a bit of smoke from the leaked oil on my engine burning off. Over the next few days it got exponentially worse until yesterday I took it to a car wash and pressure-sprayed the engine in the hopes of seeing where it was leaking. 10 miles later oil was nearly pouring out of the head gaskit. sh*t.

Current: Last night I tore my motorcycle engine down to the pistons. I've never done this before, but I followed my Clymer manual and it took about four hours. I removed the exhaust, air box, carburetor, camshafts, cylinder, cylinder head, cylinder head cover. all that's left of the motor is the crankcase with the pistons sticking out of it. Felt great to get my hands dirty. Set everything aside clearly.

So, besides the cylinder gaskit, cylinder head gaskit, the rubber square o-ring under the cylinder head (labeled CYL HEAD NO 1*0 #472153-001 on bike bandit), the breather cover gaskit, and the cylinder head cover gaskit; what else should I replace while I'm in there?
 
At 82 K miles it may or may not need a rebore I would check it & if within limits would at least replace the piston rings. Dissasemble the head decarbon, lap the valves & replace the valve seals
 
At 82k, I'd consider new valve springs also, and a cam chain.
 
top end

top end

you cannot make any decisions until you check the head for flatness the bore for tapper and if its still round, as well as the cylinder deck for flatness, you need to check the valve guides for wear using the deflection method, as well as the valve spring tension, you may also want to check the camshaft bores, once the head is apart with some plastic gauge, also consider wrist pin wear if reusing them as well as checking con rod deflection since the top is off, nothing worse than doing a top end just to have a bottom end go bad, do it right do it once
 
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