Engine burning too hot?

[-easy--rider-]

so this is the deal. i recently got the heads reconditoned on a v twin nv400 and after about 2000km i start smoking heaps and heaps and would hardly go. so i took it back to the mechanic he rang the other day and said the coils stuffed and one of the cylinders is burning too hot and it blew a hole through the piston? had never heard of this ever happening or didnt think it was possible. when the bike crapped out there was oil all in the air box and dripping out the exhausts. originaly i thought there couldve been oil coming in the airbox through a breather pipe from engine. the mechanic seemed a bit rough and i though he couldve put something back to gether rong on the head as he seemed like he was in a hurry. there are breather pipes coming from there and it could cause the engine to smoke if the airbox is full off oil.

when i got the oil back from him i checked the oil and it didnt even show up on the dip stick when cold. it just did when hot and alot of the bolts on the bike came loose so it seems like he is rough and was in a hurry and this makes me suspicious of him.

what i mainly want to know is, is what hes saying someting that can actualy happen? didnt think a hole would be able to be burnt through a piston and the engine temp was normal all the time.

[no-coast-punk]

The coils have NOTHING to do with an overly lean burn. Whoever re-assembled the thing didn't get the carb's adjusted correctly. Healthy cylinder heads vs. screwed up ones will breath COMPLETELY differently.

Have the compression checked to verify any internal damage.

The damage is basically on whoever did the re-assembly. Correctly setting fuel mixture is part of re-assembly of a top end like that. If it was you... lesson learned. If it was him... I'd be screaming for an engine.

Engine temps as shown on your instruments won't really be effected too much by a lean burn. Normal cooling will still be able to pull heat away from the cylinder jackets/heads. Pistons aren't really included in the cooling design. Surplus unburnt fuel basically acts as the "piston coolant". A lean burn means that surplus fuel for cooling just isn't there.

Have the pipes started to turn blue at all?

[-easy--rider-]

thanks alot for that. he did it and he is saposed to be a really good mechanic but i thought he was rough. it is twin carb and it was just one of the pistons he said. before it crapped out, it used to cut out if ridden for an hour or more. but then you would stop and turn it back on it would be fine again. and it seemd to only do it when it as in overdrive. do you mean the smoke or the pipes themselves turning blue?

[no-coast-punk]

Has the metal on the pipes started to turn blue? Especially at the collector right off the cylinder head.

If the pipes aren't chromed or polished disregard that.

Blued metal indicates excessively high > 800c exhaust temperatures.

Why exactly did you have the heads rebuilt? Burned valves?

[-easy--rider-]

didnt ever notice that. the water that cools it got into the head.

[no-coast-punk]

Interesting.

Typically headgaskets fail or heads warp due to excessive heat. It's fairly rare for a headgasket to simply fail for no reason unless there are a gagillion miles on a really old bike.

Based on the current failure I would be willing to bet that there was a pre-existing carb problem that caused the motor to run hot. That caused the head problem. During re-assembly the carb problem was made worse (I see this a lot. Some piece of debris that was not causing any problems will get dislodged and partially clog a jet when things are moved around.) and things ran lean enough to cook a piston instead of a headgasket.

That's just my theory based on what I've read from the other side of the planet though. I don't have all the info.

Get a compression test done to verify that there is a cooked piston. If there was a pre-existing carb problem it's less his fault than if he simply botched the re-assembly. He still should have been asking questions as to why the headgasket failure happened.

You're going to need to take it back and report what is found.

Let us know what you find.

[-easy--rider-]

the bike had about 90,000 kms on it. and now i think about it its the same head that the water was in. the mechanic has allready pulled the engine out and apart. thanks alot for the info.

[-easy--rider-]

also, the bike did used to over heat when my dad owned it because the thermostat was stuffed after we put a new one in it was fine. could that have stuffed that gasket? it couldve happend before we got the bike because it was like that when we got it.