Honda 250SX Valve Train Noises At High RPM

[kdagenais]

Hello,
I need help in finding out why my Honda 250SX has valve train noises only at the high RPM's. At idle it as quiet as it should be. Here is the curent history of the engine rebuils to help pinpoint the problem.

This engine was rebuilt with a new crank & crank bearings, new rod, cylinder was bored out to .025" then new piston and rings installed by a dealer. Bike was borught home and dropped a valve the first day after reassemby. Come to find out the timing chain was slap wore out and skipped time. I can't belive the dealer wouldn't have noticed during the reassembly that this timing chain was wore out.

So to get it running again I had to purchase a used head from ebay and then sent it to my machine shop to get clean up. I put new valves and seals into the head just for good measure. Replaced the timing chain and guides to keep it from skipping time again. Had to replace the piston again cause it had a big hole in the top.

So that is the history of the rebuild very painful and costly obviously but fortuanetly I bought from my Uncle after it dropped the valve so I didn't have pay for the first rebuild expense.
Thanks In Advance,

[heehawlittle]

sounds like you should have split the cases i have rebuilt 4 of them this year allready have one on bench right now and 3 more sitting i split cases on all my rebulds and measure the tollarance on all the gears bushings
i learned the hard way just like you did

[Dirtcrasher]

Hello,
I need help in finding out why my Honda 250SX has valve train noises only at the high RPM's. At idle it as quiet as it should be. Here is the curent history of the engine rebuils to help pinpoint the problem.

This engine was rebuilt with a new crank & crank bearings, new rod, cylinder was bored out to .025" then new piston and rings installed by a dealer. Bike was borught home and dropped a valve the first day after reassemby. Come to find out the timing chain was slap wore out and skipped time. I can't belive the dealer wouldn't have noticed during the reassembly that this timing chain was wore out.

So to get it running again I had to purchase a used head from ebay and then sent it to my machine shop to get clean up. I put new valves and seals into the head just for good measure. Replaced the timing chain and guides to keep it from skipping time again. Had to replace the piston again cause it had a big hole in the top.

So that is the history of the rebuild very painful and costly obviously but fortuanetly I bought from my Uncle after it dropped the valve so I didn't have pay for the first rebuild expense.
Thanks In Advance,

At all RPM's I have heard a valve noise and it was the cam chain, I have also heard noisy valves but setting the clearance should correct that. If that motor dropped a valve bad enough to put a hole in the piston I would assume something else got bent. Unfortunately I have no good news for you unless you haven't made certain the cam chain adjuster is good and the clearance of the valves - it's gonna have to be torn down, measured and inspected for wear and out of roundness. Doesn't sound like your in for a good time - I would harass the hell out of the mechanic/dealer as it sounds to me like you got it back and there work failed.

[kdagenais]

I have replaced the timing chain with an new one along with the slides and it is tight so that rules that out. I have replaced both intake and exhaust valves. I also had to get a used head which I had gone through by a machine shop.
The only unknown is the cam and rocker arms or possible valve adjustment. I am not sure if the cam would cause this kind of problem if it can wouldn't know what to look for if it was bad and the same goes for the rocker arms.
I performed the second rebuild myself so taking it back to the dealer is not an option. The first rebuild was done when my uncle owned the bike and when it blew up the day he brought home from there shop they said it was his fault and where not willing to help him out. :x

[Dirtcrasher]

I have replaced the timing chain with an new one along with the slides and it is tight so that rules that out. I have replaced both intake and exhaust valves. I also had to get a used head which I had gone through by a machine shop.
The only unknown is the cam and rocker arms or possible valve adjustment. I am not sure if the cam would cause this kind of problem if it can wouldn't know what to look for if it was bad and the same goes for the rocker arms.
I performed the second rebuild myself so taking it back to the dealer is not an option. The first rebuild was done when my uncle owned the bike and when it blew up the day he brought home from there shop they said it was his fault and where not willing to help him out. :x

As far as the cam goes there are specs in the manual - either the journals or the lobes themselves should not be scored along with the journals the cam rides in, the rocker arm pads that ride against the cam lobes and the rocker arm pivot shafts themselves should be smooth on the shafts and not scored or worn out. Usually if that stuffs cooked you find like aluminum paste in the head because the cam journal is wearing into the head. You also need to make sure oil is getting up there - crack that oil pipe 10MM bolt while running the engine and oil should flow right out.
Are you certain it's a top end noise?? Is it apart?? It's easy to check the cam journal to bearing when apart - just pop that rubber plug out and snug up some bolts with it on a bench resting - no cam chain etc. it is apart and it shouldn't be able to rock up and down or side to side much.

You should be able to see it if it's the top end noise - scratchy?? Nocking?? what is the noise?

[kdagenais]

Hello Dirtchaser,
It is a very fast pace knock and is definately in the top end of the engine. As far as the cam goes it is smooth as it should be. The only thing that I can figure is it is worn down. The reason for that guess is I belive it is still the original cam and this bike has a lot of time on it prior to the rebuid. My other possiblity could be the head journals from the used head I picked up could be worn to. I am not sure how to measure the head journals though.
My questions now is could either of these problems cause this knock and how to measure the head journals?
Thanks In Advance,

[whyzee]

As far as the cam goes there are specs in the manual - either the journals or the lobes themselves should not be scored along with the journals the cam rides in, the rocker arm pads that ride against the cam lobes and the rocker arm pivot shafts themselves should be smooth on the shafts and not scored or worn out. Usually if that stuffs cooked you find like aluminum paste in the head because the cam journal is wearing into the head. You also need to make sure oil is getting up there - crack that oil pipe 10MM bolt while running the engine and oil should flow right out.
Are you certain it's a top end noise?? Is it apart?? It's easy to check the cam journal to bearing when apart - just pop that rubber plug out and snug up some bolts with it on a bench resting - no cam chain etc. it is apart and it shouldn't be able to rock up and down or side to side much.

You should be able to see it if it's the top end noise - scratchy?? Nocking?? what is the noise?

Old thread complements of the search funtion.
, I seem to have developed an annoying scratching noise and a slight knocking when under load after a weekend of fairly hard riding.
Checked valves, they were in spec , compression perfect, plug was showing pretty lean so I am a bit nervous.
no smoke ever, starts and runs perfect but the sound is gross. Ideas?