blown gasket

i had the engine on my 426 rebuilt recently.I have 10 rides on that engine.runs real nice...last sunday i rode at the landing MX and i got stuck real bad..took 20 mins to get her out. the wheels were locked...finally broke her loose and away she went...when i got back to the truck i noticed some oil at the base of the cylinder at the front of the engine...after i got it cleaned up i fired it up and the culprit was a leaking lower cylinder gasket...leaking just oil , no water...the bike runs real strong and the leak is very minimal..what i want to know is , How hard is it to replace this gasket? ... i have that gasket and the top end gasket coming thursday.I have not taken a top end on a four stroke apart...

another question ,Why would this leak appear?what tips do you have to prevent this from happening again.I paid $1800.00 to get the engine rebuilt.I do not want to fu*k it up.

I did have to really labor the engine to get it un stuck from the mud...could that have been the reason for a leak?

Should I have retorqed(sp) the cylider after i got it broke in?Is that an easy thing to do?

One more question...Could something be loose that could be retightened and seal off this leak? or would gasket replacement be the only fix?

I want to do this right.



I have never had the head off of my 426, so I am not he most qualified to answer this question........but here goes.

Yes, a gasket repalcement is your only sound option. Once it has started to leak, you need to replace it.

How hard is it? Should be no harder than doing a ring job. You will have to remove the head and atleast one cam to remove the timing chain. Take the head off and then the cylinder to get at the base gasket. I have not had this motor apart, so I don't know how much of a chore it is to get the rings compressed and into the cylinder. I am not sure if you will need a ring compressor. maybe someone can chime in to that effect.

After you get the piston re-stuffed into the cylinder just install the head with a new head gasket and torque to spec. I wouldn't think that it would need a re-torque. Your new bike didn't need a re-torque from the factory. Re-install the cams at proper timing and go to the races.

For 1800 bones, what did you have done???


piston , rings, cylider ,bearings,cams, camchain,valves,gaskets, crank,+labor and shipping.. sent it to WRS in red lion PA. they did a great job with the engine...i had it out of the bike and sent it ups... i don't wanna do that for a cylinder gasket.

when i bought the bike it was used and was totally clapped out.never had proper filter maintenence and the camchain was shot.. motor jumped time and bent valves and died big time...once it got it back she was like a new beast... for that much it should be.


Wow......basicaly a new motor!!

Its not a bad job. Just a few more parts to remove. One thing to watch is the timing chain. When you are taking everything apart, the chain can (and probably will acording to Murphy) fall down into the engine. This isn't a real problem since your'e gonna take the cylinder off and have easy access to it down there, but if your engine turns (crank) it can jam the chain between the gear and other stuff down there. If that happens you will need to think about taking the flywheel off to un-stick the chain. If you are aware of it it is not a problem. Hope this helps. P.S. make sure you torque the 4 head bolts properly so you are not repeating the work.


I've unfortunately had mine apart 3 times recently (once due to a bad gasket, once due to me forgetting to put in oil, and again because the head gasket wasn't seated properly). I've never done a 2 stroke top end so I can't compare but with the manual, some patience, and preferably a friend to help hold stuff, it's not too bad. Worst parts for me were:

1) making sure timing chain didn't end up in the bottom end. I used zip-ties to secure the chain to the frame. Each time something would come off or go on (head, gasket, cylinder, etc.) I'd have to cut the tie off and secure a new one one the part was removed or installed. You'll see what I'm talking about when you do it.

2) Head removal the first time. There are two guides for the timing chain, one in the front and one in the back. The front one (closest to the front tire) can be removed once there is a small separation between the head and the cylinder. If you lift the head up a little then remove this guide it'll make taking the head all the way off easier.

3) Proper torque: my torque wrench has a big head and it was tough to get at all the bolts (#5-9 in the torque sequence from the manual). I ended up buying a 10 and 12mm crows feet wrench and using some extenders to get at them all. If you remove the engine from the frame I'm sure this is easier but it's not really necessary.

4) Lastly, I used Cometic gaskets and there is some slop in the placement on the head gasket. I think this is what caused my latest problem. Make sure you've got it centered over the cylinder before you start torquing.

As for the piston going back in the cylinder, it's pretty easy. No ring compressor is required. There are two relief arches cut into the bottom of the cylinder and it's beveled so they go in a little then you squeeze them by hand through the arches and they go in. It's really pretty easy. If you lube the cylinder and piston rings with a little engine oil I think it goes easier.

It's interesting that your engine leaked there instead of at the head. There isn't near as much pressure behind the piston as there is in the combustion chamber. If there was a torque issue with the rebuild I'd expect the head gasket to leak before the base gasket. May not hurt to closely inspect the two mating surfaces before you begin the reassembly and make sure there aren't any burrs or defects. Did the rebuild you had done involve splitting the cases? The seam where the cases meet runs right through the cylinder seating area and could be a potential leak source. Hopefully it's not that serious.

Whew, my hands are tired, I'm going to quit typing now. Good luck and let us know if you need any other help or have additional questions. -B

thank you bb... yes the base was split...when the crank was replaced...I assume it was split... anyway.if that is the source of the leak I'm screwed...I will not attempt that .


BB is right,

I know you probably will, but be sure to look for the cause of the gasket failure istead of just throwing another one on.

Good luck,

Let us know how it goes.

If you get as far as pulling the top end off and you find a lower end problem, you might as well do the labor. Sealing the cases is a easy thing. If you find that problem, let us know and Myself or someone else on the board can give you some heads up on the job.

Before you do anything, check the torque on the bolts that hold the cylinder down to the cases. If the gasget between the cylinder and cases is leaking and the job was done by a reputable shop then there is a good possibility that something may just be loose. If tightening the bolts to the proper torque fixes the leak then I would just double check the torque on the other bolts while you're there and forget about it. Just my opinion, good luck!

i took a look at cylinder with a 100w spotlight...ran the engine and got real close to the wet spot.thank god it is NOT the crankcase seals... it is leaking around the front left edge where the cylinder meets the case...I checked the bolts and they were torqued to spec. I cant beleive that the cylinder is held down in only 3 has the 2- 16 mm and the 1-8 mm bolt, unless there is some other bolt i missed.I tried to bump it a little tighter but didn't want to make it worse...It is leaking oil and coolant, it is so minor that it evaporates before it gets to drip.

I have the top and bottom gasket coming...

will i need a replacement gasket for the camchain adjuster?

and from previous posts i think the cam cover gasket can be reused.

I have a Clymers service manual with very detailed instructions.

a good freind of mine is a mechanic who will let me work on this problem in his shop with his supervision.I am really eager to learn ... especially since it cost me so much to get it rebuilt.

If anyone else has any other tips to add I would really appreciate it.we do the fix on Monday.


Chris Startt

The bolts that hold the head down, also hold the cylinder down. They are located underneath the cam cover. Did you check there torque? You should be fine with the gaskets you've already ordered. Hope everything goes well. Maniac

looking at the pics with the cam cover off, it looks like those bolts are under the camshafts...i haven't taken off the cam cover yet.they look like allen head bolts.

more questions... Why doesn't any coolant or oil leak out when the engine is off?

Also- if it was loose wouldn't the top gasket leak worse where the pressure is?


i got the gasket replaced yesterday. took 9 self and a buddy and half a case of, reread,and read the Clymers it back together...had fun finding torque wrenches..had even more find finding a magnet to pull out parts that fell down inside the engine..especially the little half rings that sit in the slots on the cam it when they take off.For the most part it wasn't that hard to get the job done...If you own one of these bikes and are not mechanically better plan to spend some money on took me 2 hours to get off everything i needed to , to get the top end getting all dirt and foregn matter cleaned off... you think you got your bike clean the last time you washed it? There are so many nooks and crannies that hold dry mud you can't count em. got her all back together...rode at the track today and all went real leaks :)

I have one question though....Is there a trick to getting the rear allenbolt off the black cover that covers the throttle cables, at the carb? I almost had to remove my rear shck to get to that damn thing.i took off the airbox and the subframe..loosened the intake boot twisted it to different was still a bitch to get to....

now...the front fork some leakage...rode in the mud for the last 4 rides...took it's toll. that and a new front tire...then well see what is next...

thanks for all your help gents...

Chris Startt

Red Lion ehhh, my kids go to school in RL :) Glad to hear you got'r back together. I should have mine together soon and I'll come down to the Landing, if you promise to come with me to Rocket Raceway. I need to ride the track anyway. They've added it to the district 7 schedule.

For pre tear down, always clean the bike as well as you can. Then when you get the seat and tank off. Wrap some saran wrap around the frame and all that crap above the head. That way you won't get any foreign objects in the motor when it's opened up.

Hope you drank the brewskis after you did the motor work :D


Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now