Laid crankcase halves together..have small gaps!

[Ndog]

Hey guys,

I finally had time to start putting my 250R motor back together. Laid the case halves together and there is two half inch areas where the cases do not lay flat. I even tightened in the case bolts to see if they pulled more together and they didnt. One spot is where they ground down the weld just a tad too much and the other spot looks like I accidently hit the surface with the polisher.

Both spots have about a 1mm gap. While thats not alot, I fear its enough to leak.

I looked at the OEM gasket in my kit and its not too thick.

With the new gasket and a nice layer of Yamabond or High temp RTV....do you think I will be ok?

If not...what should I do? This project has damn near killed me and if I get this thing on the trike and it leaks....I might die lol!!!!!

[AutoXer]

Check in the classifides freaks has a set of cases for a liquid r and he may have a set for a aircooled. did you fully polish these? Don't do all this work and chance a leak

[Ndog]

THE GAPS ARE MORE LIKE A HALF MM OR 0.5mm.

[Dirtcrasher]

^ Regardless, a half a MM is about .020 which is ALLOT. Way too much IMHO.....

Not good, better if it's away from the crank where an air leak could happen but still not good.

3 bond, hondabond etc etc does not take up thickness. It works fantastic for sealing but not making up space. You can try #1 or #2 Permagasket, which is not RTV silicone. One is soft setting, I forget which, but I'd use that one if I had to.

Sorry to say, it does not sound good bud............

[Ndog]

Gosh..sorry guys...not nearly as big as I estimated..

Only could get a 0.15mm feeler guage in there. AND YES IM SURE THAT is in MM...used the bottom metric reading.

Am in better shape?

[Bryan Raffa]

ya thats better...honda bond will work on that..put it on both sides of the case in that area and let it tac up good..

[deathman53]

bring it to a machine or motorcylce shop. They have a heavy perfectly flat wide block thats used to flatten engine cases. Some have dimples on them and others you attach some emery cloth on it. I've never used it on a engine, but I seen it done several times. I used it on a slightly warped cool-head. The depressions are usually caused by people using a screwdriver to pry the cases apart. Some 2 strokes don't use a center gasket and use a cement between 2 sides, the block is also used to remove and flatten the cement to make a good seal.

[Brad200X]

You could file the high spots as well. Somebody pryed my Airfooler's case apart with a screwdriver, I spent twenty minutes on it, and that was all it took. Just be careful. I used Hondabond instead of a center gasket BTW.

Oh yeah. You should use a Scotch Brite pad on the areas that you filed when you're done.

[Vealmonkey]

No, please don't file the high spots as this is a bad practice. It usually does more damage than good. The best method is to get a large thick piece of nice and flat glass. Then you purchase a couple of large pieces of emery cloth. Then you make sure and put some water or some type of water based lubricant and then you gently put your wavy flat side on the emery cloth and you give it a couple of gentle swirls on the emery clotch. Repeat for the other side and then put together mating surfaces and check clearances. You don't want to over do this!!! It works well if you are careful.

[Bryan Raffa]

s need that center gasket for clearance issues..

[Brad200X]

s need that center gasket for clearance issues..

How so? I broke my motor in and immediately changed the oil and didn't find any aluminum or anything... Everything spun nice too...

[johnny's X]

KEEP THE FILE AWAY! Take is to machine shop. I am not a big fan of silicone or any other fix like that. just my opinion though

[Dirtcrasher]

Maybe the is worn out a bit and could deal without the gasket, but it is designed to run one and thats built into the case machining.

He doesn't have high spots, he has low spots from a welding repair and an unintentional touch with the polisher. At this point the best he could do is the glass and emery cloth deal, just ever so slightly.

I also believe he'll be OK with 3bond as the gap is smaller than he 1st thought........

I take the high spots off of every aluminum surface I run into with a very hard toolmakers stone and WD40 or kerosene. But, I've been using those techniques for a dozen years now and I'm comfortable with it. I can see the high spots from previous mechanics disappear

Files are for large areas like an axle that had a pipe wrench on it. You can do allot of damage real quick with a file......