Tips for installing crank seals on a Stihl MS250.

[hometheaterman]

Well, I finally got around to putting my MS250 engine back together and it didn't go very well. I had a lot of trouble getting the crank seal on the side of the crank with the long shaft. It slid over the first lip fine, but it would get stuck on the lip where you put the clip. If you tried to push or twist it past there, it would pop the spring out of the back of the seal. I tried it with grease, without grease, etc. Finally after about 10 tries, I rolled up a piece of printer paper around the shaft, slide the seal on and pulled the paper out. However, when I put the engine back together and pressure tested it, it was leaking at this seal. Despite it looking fine, it had to have gotten damaged during the installation. I have a new set of seals on the way, but what's the proper way to install these without damaging it? Any advice would be appreciated.

Also, are you all putting sealant on the engine half that sits against the seal? I did as the old ones clearly had some on it, as did most YouTube videos I watched. However, the manual doesn't seem to mention it.

Here's a picture with the part circled where the seal is getting hung up. Hopefully it helps explain what I'm talking about.

 

[Pioneer]

The way you finally installed the seal is the correct way, I prefer using a very thin piece of Mylar and slide the oiled seal over it. I used sealant on the seal as you mentioned, my saw also came stock that way so why mess with success.

 

[SteveSr]

Scotch tape works good too.

All surfaces must be pristine clean before putting the sealant on. It goes all the way around the seal. I put the cylinder in a Workmate vice, correctly orient and insert the piston, flip the crank, bearings, and seals out of the way. Next add a thin bead of sealant to the seal pockets and flip the crank back in. Now put a thin bead of sealant all the way around the cylinder and seals. Install the bottom cover noting the oil pump location.

 

[farmguywithasaw]

You can pack the back of the seal with grease this will help keep the spring in place. Also grease the seal lips to help it slide on without damage.

 

[hometheaterman]

Thanks guys! It sounds like I should give it a go and just use the paper or tape or something similar from the start. I'm wondering if the tape might be better than the paper.

I also appreciate the advice on the sealant. I'd just put it where the seals sit in the lower cover. I didn't put any on the actual cylinder. It sounds like I should be putting

 

[hometheaterman]

You can pack the back of the seal with grease this will help keep the spring in place. Also grease the seal lips to help it slide on without damage.

I tried that as I've done it with other seals, but I was still struggling with this one.

 

[SteveSr]

I also appreciate the advice on the sealant. I'd just put it where the seals sit in the lower cover. I didn't put any on the actual cylinder. It sounds like I should be putting

Yea, that will make you a BIG leak. You also need to use a (silicone) sealant that is rated for high temperature and gap filling like Dirko.

Motoseal is not rated for gap filling, is non-hardening, and will blow-out during a leak test. Don't ask me how I know :-(