Cold Knocking?

[ZSK]

I went out today to start my 400 after it has been sitting for 3 weeks. Battery was drained from a short and the fuse popped so after a charge over night and a new fuse I was ready to go. Upon starting it would run for 2-3 seconds with a bad knock and die. Repeat and the same result until warm. I rode it around and noticed blue smoke (oil burning) but only if the throttle was pinned. The power was there, seemed a little low though. It's a 440 11.5:1 compression, I've been running half and half, with full premium the knock (much like I heard today) is there. I mixed it at half and half and it went away until today. Would switching to full race gas solve my problem, or is it just masking it? Is the cold just making mountains out of mole hills?

[400ex men]

did you put in a HD rod win you put in that 11:1

[ZSK]

Yup, Wisco (don't know the spelling) HD rod, FDO HD head studs, ross piston.

[Aceman]

Was the gas fresh? It almost sounds like you have a broken piston skirt that's causing piston slap. This problem is a lot less noticeable when the engine is warmed up. I also can't see how your fuel would cause it too burn oil when revved which makes me think you have piston or piston ring problem. I think you should compression test your engine, if it's low squirt some oil in there and test it again. Then you'll know what the problem is, but it sounds like a topend teardown to me.:(

[ZSK]

I did a top end tear down just a few months ago for the headstud installation. The pistion/rings/cylinder wall were all in great condition. I've also heard that the cam chain being stretched too much could make a knocking, but I'm not sure on that one.

[Aceman]

Originally posted by cleanshave300ex
I've also heard that the cam chain being stretched too much could make a knocking, but I'm not sure on that one.

I've heard that also, but I'm pretty sure the sound wouldn't go away when it was warm.

[mojoe2878]

the ex's have piston slap at cold start up, when the engine warms up the piston will expand and the knock goes away, thats normal. thats why you have to have a certian amount of piston to cylinder clearance so there is room for the expansion when it warms up. if it knocks all the time after warm up then there are other issues.
my 440 smoked a little when i nailed it for the first 4 or 5 hours after it was rebuilt, then when away, it was just time for the rings to seat good and the new valve seald to seals to swell up and seal off properly. also check your air box and air box to carb hose to see if there is oil in it from crank case blow by.

[ZSK]

I should have been more specific, the knock is there even when warmed up. It speeds up with more rpm's, and is very predominate at idle. On the vent tube from the case to the airbox hose it is very black, and looks like oil. What can be done about that?

[mojoe2878]

after you saying that, then it sounds like you have a cracked piston or broken ring. it would still have enough compression to run in most cases but the knock will be there like you say and it will cause air to be pulled into the crank case on the down stroke through the crack or broken ring and letting the oil blow by thru the case tube into you air box hose.

[rneal]

try replacing your cam chain tensioner. I had a similar sound occuring and after adjustibg my valves the noise didn't go away. I figured before tearing the motor down I would relpace the tensioner to see if it made a difference. It solved my problem and I'm running smoother than I can ever remember.