400ex is knocking.can u help

[crewworrior]

my friend has a 99 400ex that just started knocking and smoking all at once, does anyone know what this might be, it hasn't lost any power ,and the knock sounds like its coming from the bottom end, and theres oil coming out of the pipe. if anyone can help i would greatly appreciate it.
thanks

[400eXr1d3rZ]

Is it burning oil? Bluish Purple smoke?

[crewworrior]

yea its blue smells like its burning oil

[400eXr1d3rZ]

Replace valve seals.

[flauge]

Im no expert but ive always heard the knocking could be from a worn rod or crank bearing... sorry man:scary:

[250X_project]

Yeah, You deffinitely have more trouble than valve seals. A knock from the bottom end is probably the main bearings on your crank. It could also be the needle bearings in the bottom end of the rod on the crank pin. Also if it's not the BOTTOM, bottom than it could be exessive piston to cylinder clearance. This would also cause oil burning. Run a compression test to see how worn the rings, valves, and head gasket is.

Let us know what you get for a reading.

Does it get hotter than usual?

[crewworrior]

i dont have a compression guage but ill try to get one,i kinda thought it might be the crank bearings myself but i wanted to get some more opinions.the head gasket looks like its leaking and the intake boot that connects the carb to the cylinder is busted too.i think were just gonna tear the whole engine down and go through it. it doesnt seem to be running hot,and has plenty of power. thanks for the help and let me know what you think.

[crewworrior]

Originally posted by 250X_project
Yeah, You deffinitely have more trouble than valve seals. A knock from the bottom end is probably the main bearings on your crank. It could also be the needle bearings in the bottom end of the rod on the crank pin. Also if it's not the BOTTOM, bottom than it could be exessive piston to cylinder clearance. This would also cause oil burning. Run a compression test to see how worn the rings, valves, and head gasket is.

Let us know what you get for a reading.

Does it get hotter than usual?

it doesnt seem to be getting hot

[250X_project]

If it is an actual knock coming from the bottom end, than I would have to say it is the main bearings on your crank.

Though, if it is a ticking up top, 400EX's are known for the cam chains, and cam chain tensioners.

Do you have an Advanced Auto shop near you? That is where I got my compression tester. I couldn't be happier with it.

[Lukeidiot]

Advice 1: Check oil, if empty, you'll have to replace piston/head

Advice 2: A valve adjustment

[m.h.s.c.#527]

Originally posted by 250X_project
If it is an actual knock coming from the bottom end, than I would have to say it is the main bearings on your crank.

Though, if it is a ticking up top, 400EX's are known for the cam chains, and cam chain tensioners.

Do you have an Advanced Auto shop near you? That is where I got my compression tester. I couldn't be happier with it.


yea my 250 is in the shop and they called and said the cam chain tensioner was out of adjustmment

[crewworrior]

i thought that the tensioner adjusted its self,its full of oil,and does anyone know if the 400 has crank seals because i can only find the bearings with no seals,im kinda thinking that the knock is coming from the crank bearings and the smoke is coming from the rings because of the play that the worn bearing allow in the piston. what do you guys think. also i checked the valves there within specs, and the cam chain is tight.

[250X_project]

You shouldn't have crank seals. Also your cam chain tensioner should be self-adjusting, but can get worn and alow slack in the chain. A compression test will tell you if your piston and rings are still good, yet a high compression piston will give it better power. you'll be in there anyway, so why not a new piston?

just my 2 cents ;)

[CDCHONDAS]

Originally posted by Lukeidiot
Advice 1: Check oil, if empty, you'll have to replace piston/head

Advice 2: A valve adjustment

Not much there I would listen to.

A serious bottom end knock would normally come from the large rod end rather than the crank bearings, crank bearings can to bad but the rod normally does first. FYI these are not like car engines and the main bearings are bearings with balls in them (if I said ball bearing you would all think of slingshots) as where the rod bearing is needles., on a car its just soft metal, the only real similarity is the rod on both is pressure fed.

[crewworrior]

i talked to a man yesterday and he says that he would check the cam chain tensioner,and that its smoking because the head studs are streched,this is probably what im going to do first because its alot easier and cheaper than tareing into the engine.

[Which 450?]

Originally posted by crewworrior
i talked to a man yesterday and he says that he would check the cam chain tensioner,and that its smoking because the head studs are streched,this is probably what im going to do first because its alot easier and cheaper than tareing into the engine.

because the head studs are stretched?? Ive never heard more crazy ideas in this thread about what the problem could be.

[250X_project]

Yeah, I don't see that being any part of the cause either. If the studs were stretched they may cause a lose in compression, which people often associate with oil burning, because of ring wear. That is the only reason I see anyone would say such a thing.

Also the cam chain and/or tensioner would not be a knock, rather a ticking or a rattle. It would be on the top end of your engine as well.