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Discussion Starter #1
Hi there I recently had the top end of the engine in my kodiak 400 rebuilt due to smoking after overrun. It had a new valve, valve guides, valves seals and the valves were lapped. It started streight up no problem and runs well but still there is smoke, now not just on over run but at other inconsistant points. I didnt change the rings but the bore was perfect with no lip etc. The shop i had the head work done at has advised i run it and to "bed in " but fo valve guides burn oil when bedding in like piston rings? It may have improved very slightly in the 5 miles since reassembley , although that could just be it warming up? Many thanks
 

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smoki

Hi there I recently had the top end of the engine in my kodiak 400 rebuilt due to smoking after overrun. It had a new valve, valve guides, valves seals and the valves were lapped. It started streight up no problem and runs well but still there is smoke, now not just on over run but at other inconsistant points. I didnt change the rings but the bore was perfect with no lip etc. The shop i had the head work done at has advised i run it and to "bed in " but fo valve guides burn oil when bedding in like piston rings? It may have improved very slightly in the 5 miles since reassembley , although that could just be it warming up? Many thanks
did u do a leak down test before you took it apart ???.
just run it and burn off the excess oil in the muffler....mine smoked like a chimney for some time after rebuilding the top end...rings had to seat and lots of oil residue in the muffler
 

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The engine shop is taking telling BS. There is no bedding or seating in of the valve seals and guides.
You lap the valves to the valve seats using valve grinding compound to seal them. This is done on the bench. There is no seating or bedding them in on operation.

The rings are more than likely worn. They may "look" good, but they may not be good.

You could have oil in the muffler, but this does not usually cause intermittent smoking. This almost always causing a consistent smoke (especially once the mffler gets up to operating temperature) until all the oil is burned off.

Right now since you got it all put back together, do a leak down test. You'll need to start with these results.
 

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You really should have installed fresh rings while you had it apart. Do a leak down test.
 

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Discussion Starter #6
Hi there, ive tried to respond a couple of times today but it doesnt seem to be working. Ive torn the engine apart again and took the bore off, it doesnt seem to be any worse than i tgought exept a bit of a lip i didnt pock up before at the top where rarther than being silver the bore looks gold. The rings arent cracked. Ive ordered an oversized piston but its made by a comapny caled namura and after a bit of research im not sure if i should cancel it as there seems there may be a few quality issues? The head doesnt seem to leak fluid past the valves. Do i definatly need to go oversized or would just new rings do the trick? Cheers
 

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Did you measure your piston and cylinder to verify if they are in spec? Why do you assume you even need an overbore / bigger piston in the first place?

Just because rings look ok doesn't mean anything. A proper cylinder leakdown test would have verified if your rings were sealing without even taking the engine apart. Though it is possible that your oil control ring simply isn't doing its job, witch is why it should have been replaced the first time around.

Now that the engine is apart, do you see oil dripping down your valves? Check out the photo, these were leaking exhaust seals on my classic car after a complete engine rebuild . The intakes ports were also covered with oil from bad batch of int/exh valve seals.
 

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Did you measure your piston and cylinder to verify if they are in spec? Why do you assume you even need and overbore / bigger piston in the first place?

Just because rings look ok doesn't mean anything. A proper cylinder leakdown test would have verified if your rings were sealing without even taking the engine apart. Though it is possible that your oil control ring simply isn't doing its job, witch is why it should have been replaced the first time around.

Now that the engine is apart, do you see oil dripping down your valves? Check out the photo, these were leaking exhaust seals on my classic car after a complete engine rebuild . The intakes ports were also covered with oil from bad batch of int/exh valve seals.
x2...completely agree.

In your first post you stated the bore was perfect. How did you come to this conclusion? Did you mic the cylinder bore? Is cross-hatching still visible?

Before assuming anything or throwing parts at it, have the cylinder properly measured. Once you know the condition of the cylinder, then you make the correct decision on what your next step would be.

In most cases, unless the engine has been abused, sunk or over-heated, the cylinder bores and piston are fine, but rings will be worn.....but this should not be assumed. The cylinder should be measured to know for sure. Trust us on this. Taking a little extra time to have it measured and knowing for sure leads to a much less aggravating experience. It will actually save time and money in the long run with a properly repaired and reliable ride.

Replace the piston rings either way. I always replace piston rings if I remove a cylinder.

Keep us updated as well.
 

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smoke

Just measure the piston ring end gap...that will tell you the story...when i did mine i had like .070.. bore was fine as was the piston but a leak down test told me the rings were not sealing...
 
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