2 stroke crankcase pressure? Lot or little?

[Super350]

I had to have a set of 2 stroke cases welded at the bottom end just below the crank area. The welder ground down his welds on the mating surface a bit and I think he may have hit the non-welded area a bit leaving a slight depression. Im having the mating surfaces machined (taking down the welds to the original deck) but due to his grinding this may result in a very small gap between the 2 cases. These are match ground cases from factory with no center gasket but you do use a sealer.

So my question is how much pressure is there inside the cases in the crank area? Do you think sealer will hold or should I have the gap filled and then re-machine the mating surface?

I realize this is a judgment call but the gap is very very small and I just didn't know how much pressure there actually is in there. Im most likely going to fix it proper but I just figured id ask. thanks

[oscarmayer]

if ti's done right there shoudl not be enough to blow through hondabond. if it's done wrong you'll blow the Hondabond out.

[RIDE-RED 250r]

Well, there will be altering pulses of pressure AND vacuum.

Oscar is right.

Might try this as a little insurance so you can run it before you get it fixed "proper". Apply a skim coat of epoxy or JB Weld in the area of concern. Make sure you leave it a little high and extending beyond both ends of the low spot. Once fully cured, you can use a sanding block to work it down flush again, being careful not to go too far. But using a good straight sanding block and not going crazy on it should get you pretty darned close to good to go! If you need to take alot of material down and sanding is going too slow, use a flat file to get the bulk of it down and finish with the sanding block. Just be mindful of the surrounding existing aluminum that you don't create another low spot.

This may sound a little too redneck for some, but it DOES WORK! I have done it myself. Just make sure and prep the surfaces properly so the JB Weld or epoxy adheres as it should.

[Super350]

thanks for the reply's guys!

Red - I had thought of doing what you described but was worried about using J.B. incase I needed to split the cases again in the future. Or could I just sand it all off to split them? thanks

[fabiodriven]

I wouldn't hesitate to use JB Weld. When used properly it is a permanent repair. You'll always be able to split the cases later, no problem with that. Just make sure it's done correctly and it will last forever.

[onformula1]

thanks for the reply's guys!

Red - I had thought of doing what you described but was worried about using J.B. incase I needed to split the cases again in the future. Or could I just sand it all off to split them? thanks

Hold on, he is talking about putting JB Weld on the sealing part of the cases (The lip if you will)

You will not have to grind or sand anything down to split the cases in the future.

And yes it works great.

I have seen box stock cases with casting prosperity problems and the JB works.

[RIDE-RED 250r]

Yeah, I'm not talking about putting the cases together and applying JB over the questionable area on the outside. I am referring to using the JB as a shim of sorts.

Apply it as I described. Then apply your Threebond or whichever sealant and assemble the crankcase as you normally would.

Fixed!

I made this type of repair on the deck of one of my 250r engines that had a couple of divots from some jackwagon using a screwdriver to pry the cylinder free of the case sometime in the past. Still runs and passes leak-down test to this day.

[SUPERBEAST]

are you guys talking about using the putty sticks or the 2 tubes you mix together?

[RIDE-RED 250r]

Use the tubes. The JB stick is too thick and clay-like for this type of application IMHO. The regular JB Weld or JB Quick Weld in the 2 tubes is thinner and I think will adhere to the aluminum better in this type of situation.

I used JB Quick Weld on my repair and it worked great.

I have also used the JB stick weld in other applications and while it worked well in those situations, I don't think the type of repair we are discussing is one it is best suited for.

[SUPERBEAST]

good info on the jb weld

[Super350]

I totally thought you were saying assemble the motor and then apply the JB to the outside over the questionable area...which is what I was thinking. But your saying apply it to the mating surfaces, the actual edges that come together? Doesn't that make them "weld" together and not want to come apart in the future? I believe you guys for sure I just never would have done that

[onformula1]

You apply it to the sealing edges where the damage is and let it dry per the instructions then sand it smooth they clean up the dust mess then put it back together with your sealer

[fabiodriven]

It is an epoxy but it's solid once cured and can be cut, formed, and machined.

[Super350]

right on boys! thanks for all the input

[RIDE-RED 250r]

Onformula1 and Fabio are correct.

I am not talking about slathering JB over a leaky gasket/seam on an assembled engine. I am talking about re-forming the actual sealing/mating surface with JB Weld and then putting the halves together once cured.

[RubberSalt]

The answer to the question depends on the engine. Modern engines have low pressure, older engines had higher pressure. Your looking at 7-8psi tops on any of them.

[atc300r]

I sent my cases to BDT and had the crank area fixed. They welded and machined the gasket surface they mate together very nicly. Im waiting on gaskets to get it back together.before and after pics. Once you get the JB weld on and cured get 3-4 sheets of fine sand paper an a smooth surface tape the sand paper to the smooth surface sand side up and put your case on it gasket surface down put slight pressure and do small circular motion . This will smooth it out. 213014 213015

[RubberSalt]

They did a pretty good job with that. JB only goes so far lol