blown head gasket.

[1fst400]

I just got my motor rebuilt.... I did the work, know I did it correct, quadruple checked every step.


I just had the motor completely aprart, replaced some tranny gears, crankshaft, piston, flywheel, clutch, clutch hub.

I got it together like 4 days ago, went riding 1st day, everything went good. started developing spark knock by end of ride (1hr).

next ride, spark knock verry bad, bump main jet from 175 to 180

Today, spark knock not quite as bad. Try puting tape on air filter to richen it up more (dont have a bigger jet). get to the point where it boggs from to rich, still knocking.:confused:

I called c&d, talked to colby. He gave me a cupple idears, but w/o hearing it in 1st person it is hard to figure out the problem. thats fine, I understand.

So I go riding again, let a budie drive it. He comes back after about 5 min, head gasket it blown. All compression is blowing out side of motor. All well I knew somthign was up, no big deal.


Why do you think it blew?

Here is a list of everything Im running in my motor.

Im running 12:1 je piston. cosmetic thin gaskets, hotcams stage 2, kibble white oversized valves w/ 3 angle valve job, porting, fcr carb, hot rods HD crankshaft, stock weight flywheel, sparks clutch, Wite bros rev box, crf timing chain, hinson clutch basket. think thats it.

And I'm running this all on c12 non deluted.

I know that I tightened the head studs good, I tightened them to 38ft lbs I believe.

[prepracing]

are you running stock bore with a 12:1 or an oversize bore with 12:1 ??? Oversize bores with 12:1 compression can pull head studs out of the head ( strip the holes ) due to the compression. You can buy an oversize stud kit that will eliminate the problem. Unless the stud bolts/nuts just happened to back off or its a bad gasket set ( but if it was bad gaskets I would think that would have happened 1st thing when you ran it ). I have seen studs back off, so double check them and see whats up.

[Glamis400ex]

Get HD studs. I only know 1 person running 12:1 on stock studs. Don't know how, but he is.

[1fst400]

wups forgot to mention, have hd studs and 416cc bore.

[boondockman]

I think you might have overtightned your headstuds,my service manual says 33ft lbs.

sounds like you need a piston return spring

you can get on here http://kalecoauto.com/index.php?main_page=product_info&cPath=3&products_id=27

[1fst400]

I have never heard of a piston return spring.. wtf is it.


I dont think that 38 is to much, that is what I was reccomened by a motor builder.

[Glamis400ex]

My FDO studs were set at a recommended 33 #'s

[bradley300]

make sure the carb boots and air filter are on tight. if not, they would suck in air, causing your lean mix. have you had this set up b4 and are just doing a rebuild, or is this a new set up? maybe the lean jetting got something hot and something had to give

[1fst400]

I just checked the carb boot and air filter, both on good.

This is a rebuilt built motor, Before I was running a 416 with 10.8:1 piston. Now I'm running 12:1 with hotrods crank on same 416 bore.


Im going to tear it doun in about an hour. I just gave the bike a bath first. And Im waiting for it to dry..

[1fst400]

oh and I doubt the motor got over heated. Its possible, but it was about 40 degree's out. And it was only ran for all of 10 mintues on the day it blew. It was ran for a good 3 hours scence rebuild.

[1fst400]

pic of the gasket, it totally destroyed it. head bolts wernt tight:confused: :confused: ???

The bolts may not have been tight because there was gasket missing or that they loosened then the gasket blew.

either way, I still dono why the motor was knocking.

[1fst400]

Put it back together with a new head gasket. Thing runs flawlessly,:confused: :confused: :confused: ????
NO knocking, nothing. Way more power than the first time it was together.

[nakomis0]

I got an idea.:macho

Re tighten the head studs.... like you suppose to do after an hour or so of riding. Heck maybe even check em again after another few hours.

Even the gaskets they make that they say you don't need to re tighten I would check and re tighten if needed.

Manuals are great too,