89 LT 250R keeps blowing base gaskets?

[Mosh]

Posting this for a friend.

He has a 89 Lt 250R. Last year his base gasket blew right below the reed cage.
So he did a top end job on it, and New PWK 38 mil carb.
after 10 hours ride time, he blows the base gasket again.
He puts a new gasket in, and 4 hours later it blows again.

So he grabs his extra bottom end, that had no problems.
Buys a different jug, sends it out for boring, and has the bottom of the jug decked.
He installs it with a OEM base gasket, and 1 ride it blows the gasket too..

He has decked the jug, tried different bottom ends, Wiesco gaskets, Cometeic gaskets, OEM gaskets.....
And the thing keeps blowing the base gasket right below the reed valve area where the jug meets the block.

He has used hi tack, double base gaskets...Everything he can think of.

He is getting frustrated so I wanted to toss this up and see if anyone has seen this problem before..

Keep in mind...2 Different jugs..1 was milled flat again...2 differend bottom ends..Every time with both combinations, the base gasket blows right below the reed valve in the same spot, no matter what jug or motor or gasket he uses.

His mods are Wiesco pro lite pistons, PWK 39 mil carb, Stock reed cage with Boyeson reeds, and a FMF pipe.

Anyone have any ideas for him?
He is at his wits end....

The bike runs like a scalded dog, for about one ride then it pops the base gasket..

Is the PWK 38 mil carb creating too much crankcase pressure?
There are no symptoms at all.
Crank case seals seem fine, it isnt sucking crank case oil in anywhere..

[RodKnockRacing]

the only thing i can think of is not torquing the bolts down or the gaskets arnt the right ones a guy i knew had that problem and it was because the gaskets werent a perfect match

[Jason Hall]

A few things come to mind when I think about that. The first Is, could he be tightening one corner of the cylinder Very Tight before snugging the opposite corner???? Could one dowl pin be bottoming out before the 2 mating surface's touch. If all else fails, then find some RITE STUFF!!! I swear by the stuff!!!! It's 14.00 for a small caulk tube, but will seal about ANYTHING. I use It on Caterpillar front engine covers, and they Never leak again.

Rite Stuff silicone made by Permatex. If you can't make It seal otherwise, I suggest he double up the base gaskets. Put a thin coat of rite stuff on the bottom of the first gasket (put the coated surface facing Down case side) On th second gasket put a thin coat on the top (Jug Side). Now you have the 2 gasket surfaces touching, along with a sweet seal on each surface!!! Let that baby dry over night, and he shouls have It. The trick Is to not Glob the sealer, just use a Skimm coat.

[SWIGIN]

my 89 did this after i turboed my crank with 240psi cly presure....but it would suck it in right under the reeds.

check the cly presure try to keep it no higher then 220psi.

[sblt500r]

get a cometic RCM gasket. rubber coated metal. stronger then a paper gasket. come in different thicknesses to.

it does sound like its not torqued correctly, or a stud is pulling out of the cases

[Mosh]

Ok thanks guys.

I will see if he will pull the motor and bring it to me, for dowel / stud inspection.
Then I will assemble it for him.

I will advise him of that Cometic gasket SBLT..I like them things.They work well.

If that is not an option, I will go with the "right stuff" that Jason suggested.

[Yamada]

A few things come to mind when I think about that. The first Is, could he be tightening one corner of the cylinder Very Tight before snugging the opposite corner???? Could one dowl pin be bottoming out before the 2 mating surface's touch. If all else fails, then find some RITE STUFF!!! I swear by the stuff!!!! It's 14.00 for a small caulk tube, but will seal about ANYTHING. I use It on Caterpillar front engine covers, and they Never leak again.

Rite Stuff silicone made by Permatex. If you can't make It seal otherwise, I suggest he double up the base gaskets. Put a thin coat of rite stuff on the bottom of the first gasket (put the coated surface facing Down case side) On th second gasket put a thin coat on the top (Jug Side). Now you have the 2 gasket surfaces touching, along with a sweet seal on each surface!!! Let that baby dry over night, and he shouls have It. The trick Is to not Glob the sealer, just use a Skimm coat.

The only thing I have to add to this is that on a Toyota Tercel I used the rite stuff to seal the motor oil pan. There is no gasket that goes there. Coat the parts, assemble, let dry overnight. This stuff is oil and gas resistant.

[cr480r]

lt250's almost always need to be machined to eliminate misalignment of the case halves. after the cases are fixed its best to remove the head stay and use copper base gaskets or try the rcm gaskes mentioned above. if you are heavy guy or jump alot the base gasket will blow everytime if the head stay is used.. good luck!

[SWIGIN]

lt250's almost always need to be machined to eliminate misalignment of the case halves. after the cases are fixed its best to remove the head stay and use copper base gaskets or try the rcm gaskes mentioned above. if you are heavy guy or jump alot the base gasket will blow everytime if the head stay is used.. good luck!

um...... im a big guy and i raced a lt250 just about all through the 90s and i have to call BS to the head stay thing.

[lndy650]

i was thinking cr480r must be joking lol

[300rman]

i second the mis-torqued studs or a stud pulling out.

[Saul]

To get a better base gasket seal you can take a good quality punch and make a small indentation every 3/8's of an inch around the base.