Compression Leak

[Escobar]

Hey Guys,

Got a ’04 Mastiff (107) Left side drive. Need a little advice on the level of difficulty I’m looking at for tearing my heads apart and replacing the gaskets. I went out for a ride this weekend and developed compression leak on my front cylinder (left side) between the upper and lower portion of the head, opposite side of the pushrods. I’m a decent mechanic… at least I think so; I do all my own work on all my cars and bikes anything from simple oil change to swapping out motors and even rebuilt my big dog when I got it from an auction wrecked. I’ve got no problem tearing it down and putting it back together but I've never actually had to break into the cylinders on the bike or adjust the pushrods. I’ve got the BDM service manual with all the torque specs and I think even some info on the pushrods but I figured there’s that’s done this before and could just give me an idea of what I’m looking at. From a glance this weekend I figure I’d have to start by removing the gas tank, spark plugs, coil cover, exhaust and the carburetor but I’m not sure if I’d be able to work on it with the frame backbone in the way. I did find a link in the “How to” from Raywood on Top end rebuild for an ’05 so that’s where I’ll start for now. Sure hope I can get it done before Novembers Rally; I’ve already got my room.

(http://www.bigdogbiker.com/forums/how/15092-top-end-rebuild.html)

Thanks,

 

[john sachs]

First thing you need to determine is if there's a stud pulling out of the case. :angry: You can check that by setting a torque wrench at 38 ft. lbs.,and see if the head bolts on that cylinder will hold that.Do it before taking it apart.Even if it does hold,you still need to look at the stud in the area of the leak,when you get it apart,to visually see that it hasen't tried pulling.
Check the head gasket area of the head,and the top of the cylinder to be sure you haven't burned a trough on either surface.
Level of difficulty is no different than removing the top end of a motor. :up:
John

 

[mobsta]

Very easy but like Mr. Sachs said make sure your studs aren't pulling.I made that mistake on my 04.Put new head gasket in blew in 15miles.pulled apart and found studs pulled.About 1000 miles later the other cyclinder studs pulled.sucks since the motor was rebuilt by s/s 2500 miles pryor.hope it all works out for you.

 

[Daddycool]

if you do take the head off, dont move the piston or you could lift the clyinder off the base gasket. If that happens then it will also leak and you'll need some ring compressors to get the piston back in the cylinder after you change the base gasket.

 

[john sachs]

if you do take the head off, dont move the piston or you could lift the clyinder off the base gasket. If that happens then it will also leak and you'll need some ring compressors to get the piston back in the cylinder after you change the base gasket.

I ALWAYS make a habit of replacing the base gaskets once the heads are off......If not you'll PROLLY HAVE A LEAK. :bang:
Use only S&S gaskets,and torque values.This way,no one can say you deviated from the factory assembly. :up:
John

 

[Escobar]

Thanks for the advice guys; I'll tear into it this weekend.

John, Do you know of a link where I can find the torque values for my Motor. It's probably in the service manual but it would still be a good reference.

Thanks again! :2thumbs:

 

[john sachs]

Thanks for the advice guys; I'll tear into it this weekend.

John, Do you know of a link where I can find the torque values for my Motor. It's probably in the service manual but it would still be a good reference.

Thanks again! :2thumbs:

S&S is 8 ft. lbs. then 18 ft. lbs. then 90 degrees.
I usually bump the 8 & 18 by 2 ft. lbs. each.If you do,it's your decision/responsibility, NOT mine.
John

 

[MARV]

Thanks for the advice guys; I'll tear into it this weekend.

John, Do you know of a link where I can find the torque values for my Motor. It's probably in the service manual but it would still be a good reference.

Thanks again! :2thumbs:

you should get the S&S 4.125 manual for 20 some odd bucks

its the holy grail

 

[Escobar]

you should get the S&S 4.125 manual for 20 some odd bucks

its the holy grail

I'll pick it up, thanks!

 

[Escobar]

S&S is 8 ft. lbs. then 18 ft. lbs. then 90 degrees.
I usually bump the 8 & 18 by 2 ft. lbs. each.If you do,it's your decision/responsibility, NOT mine.
John

Got it! thanks