Question about crank case seals during reassembly after splitting a case - Dolmar 6421

[sevensandeights]

Working on a Dolmar 6421 that I had to split the case due to failed case gasket letting bar oil into the crank case.

Saw is all apart/cleaned and I just got notice my parts have arrived. Planning to reassemble today. Do you typically install the case seal prior to putting the case back together? If so, any concern about distorting the seal if you have to heat the bearing to accept the crankshaft?

Also, I only separated the case to get to the gasket. Pressed the crank out of the flywheel side. The clutch side of the case still has the crank attached (through the bearing) and seal intact. I shouldn't need replace that seal, correct?

 

[jacob j.]

If the seal on the PTO side is still in good shape and you've left the crank in that side of the case, then yes, you should not have to replace that seal. You'll want to replace the flywheel side seal after you've assembled the case with a new gasket. The flywheel side seal is pretty easy - I lubricate the lip of the seal good before starting to work it into the pocket. You'll want to make sure the lip of the seal gets over the shoulder on the crank without rolling. I think the crank is tapered well on that side so it should be pretty easy.

 

[hacskaroly]

Also, I only separated the case to get to the gasket.

Welcome to the forum!! I agree with JJ, if the PTO side is in good shape, no need to touch it, otherwise put the casehalves back together with the new gasket and then when complete, go ahead in install the new oil seal on the at the end, that way if you have to heat anything, you are not risking damaging the oil seal. I have done it that way for several saws and it has all worked out great with no damage to the oil seals, just have to watch and make sure they don't roll as you are installing them.

I don't use heat when putting a case back together, the tools I have don't require it, but I still wait until the case halves are back together before installing the oil seals.

 

[sevensandeights]

Thanks all - very helpful!

Saw a video (from MattyO) of the pop can trick for the seal so might try that to prevent the lip from rolling.

 

[hacskaroly]

Saw a video (from MattyO) of the pop can trick for the seal so might try that to prevent the lip from rolling.

Yeah, good stuff, I bought the tool set he sells for pulling cases together!

 

[Shane¹]

There is a good taper on the flywheel side I am sure it will slide together fine and you won't even need a new seal

 

[sevensandeights]

There is a good taper on the flywheel side I am sure it will slide together fine and you won't even need a new seal

Good advice - thanks!

Do you recommend anything for getting the cases back together when just the flywheel side of the crank needs to go through the bearing?

 

[Shane¹]

Flywheel side usually goes together really easy. Maybe the slightest amount of heat with a heat gun but I bet you will find flywheel side will almost slide together

 

[sevensandeights]

That would be awesome.

 

[huskihl]

Like mentioned, the flywheel side isn’t so bad. And some clutch sides aren’t bad, depending on how the crank is designed. If there is a step on the crank, it’s much more difficult to pull the crank case halves together with that seal in place. Even for people that do it often, most aren’t willing to add more fuel to the fire by dicking around with that crank seal in place. Much easier to lay the saw on its side, absolutely use the pop can trick or a sheet of thin plastic, lube the seal up well and push it in as straight as possible

 

[Shane¹]

I like using a plastic McDonald's cup for putting seals in they are so thin and work great but the flywheel side has a good taper I think you will be fine without anything just maybe a little lube

 

[Duce]

Like mentioned, the flywheel side isn’t so bad. And some clutch sides aren’t bad, depending on how the crank is designed. If there is a step on the crank, it’s much more difficult to pull the crank case halves together with that seal in place. Even for people that do it often, most aren’t willing to add more fuel to the fire by dicking around with that crank seal in place. Much easier to lay the saw on its side, absolutely use the pop can trick or a sheet of thin plastic, lube the seal up well and push it in as straight as possible

I agree. Have had to tap seal in place with deep well socket or small piece of pipe, then motoseal around metal flange. Have a few washers that fit over shaft and seat seal nice.

 

[huskihl]

I agree. Have had to tap seal in place with deep well socket or small piece of pipe, then motoseal around metal flange. Have a few washers that fit over shaft and seat seal nice.

Never thought about the washer idea. Solid

 

[sevensandeights]

Do any of you guys routinely pressure/vac test before putting everything back together? I have a Mityvac - just haven't used it in awhile so will have to see what kind of block off plates/plugs I have. I know I made a block off cover for the exhaust side of the cylinder but think I've only ever tested the intake side with the carb on.

 

[hacskaroly]

Never thought about the washer idea. Solid

I use washers, they evenly cover the oil seal and press it in equally, very simple process for people like me with two left hands and two left feet!!

 

[huskihl]

Do any of you guys routinely pressure/vac test before putting everything back together? I have a Mityvac - just haven't used it in awhile so will have to see what kind of block off plates/plugs I have. I know I made a block off cover for the exhaust side of the cylinder but think I've only ever tested the intake side with the carb on.

Double up some duct tape the width of the inside of the bolts and pinch it between the muffler and flange. Do the same thing on the carburetor side between the carburetor and boot. You can test through the impulse line. I usually check everything after I fix an air leak to be certain I got it. I don’t vacuum test every saw before replacing seals though

 

[hacskaroly]

Double up some duct tape the width of the inside of the bolts and pinch it between the muffler and flange. Do the same thing on the carburetor side between the carburetor and boot.

Genius idea!! Thanks!!

 

[sevensandeights]

Slick tip - thanks!