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moto4 smoking - valves and/or head gasket?

6475 Views 4 Replies 2 Participants Last post by  dezz
Got this 89 Moto4 350 running but it smokes. Thinking this was a slam dunk piston ring/clearance issue, I took the head and cylinder off but man, the piston and rings look good as does the cylinder bore. I mic'd it out at 82.98 in a few different places so it seems tight. I also dont notice any blow by on the piston. The engine leaks oil out the front down the cylinder and on the starter so the O ring and/or head gasket has failed there. If it leaks out, I guess its possible it also sucks oil into the chamber and its burning off?

At any rate, I ordered a new top end gasket kit and am also going to be replacing the valve guide seals. I'm stumped as to why the engine is burning so much oil but hopefully replacing these parts will solve it. I didn't have the correct adapter to check compression and I'm kicking myself for assuming it was just rings. It also ticks a bit which is the timing chain, but after listening to youtube videos about loose chains, mine is nowhere near as loud as those are. If it needs to be replaced, I can do it at a later time fairly easily. I'll be doing a light hone on the cylinder before putting it back on.

Valve clearance was within spec, .06 for intake, .18 for exhaust as well. What else should I be looking at?


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Valve seals are more than likely the culprit. Being this old, they could be dried and leaking.

I would replace rings too. You already got it apart, and rings are cheap. No matter how good the piston and cylinder look, the rings could still be worn.
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I put in an order for a new set of rings also on your recommendation which is good because as I was taking the old set off, the middle ring was brittle and it cracked. The valve spring compressor hopefully will be here this week as will the rest of the parts on Friday/Saturday so maybe I'll be able to get it all back together and be riding it Saturday or Sunday. /cross fingers.

How do I get the rocker arms out? The pin they ride on is pressed in and I can't get to the opposite side to press it out.

Looks like I need to use my slide hammer and pull it out as they are threaded.. no biggie.
Update to my post, I disassembled the head completely and soaked it and the cylinder in parts cleaning solution overnight and brushed them clean, along with the valves. I lapped the valves gently with valve grinding compound and reassembled everything with new valve guide seals. I did have to tap the rocker arm dowels as they are supposed to be M6 x 1.0 but someone had buggered the threads, but that was painless and they came out after fixing them.

Rings I ordered weren't an exact match. I guess my piston isnt OEM? because one of the rings was too thick, so I reused one of my old rings and new oil rings (3) and a new top ring, and everything buttoned up fine along with new gaskets.

Fired up and has considerably less smoking than before, and I took it up and down the block, brought it back into the garage, and did an oil and filter change. UGH, there was a lot of crud in the oil filter cavity, so I flushed it all out, drained the cooler, and the oil was disgusting soupy black and very runny, but didn't smell like fuel.

New oil, filter, everything cleaned up, and she purrs and after another 10 minutes of idle, and light throttle play, 99% of the smoking is gone. I think once I run it hot and get everything warmed up, seated, and burned off, it will be a success.
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Thanks for the update. We appreciate it.
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