Installing Crank Seals Without Lubrication

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Mr. Piste

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Greetings and salutations!

I am in the midst of rebuilding a Stihl MS361, and am installing a brand new OEM top end (as the last one was shish kabobed as the result of a disconnected impulse line). I have decided to replace the old and worn crank seals as a precaution against possibly burning up aforementioned top end (nothing would frost me more). I started with the PTO side. I applied a bit of Stihl Ultra on the crank bearings, and made darn sure that there wasn't even the smallest spec of dust present in the assembly before I installed the new seal. The new seal went in without any trouble, but I realized once I had gotten it into place that I had forgotten to lubricate the seal in any way, whatsoever. There was a small amount of Ultra on the crankshaft in and around where the seal sits when I installed it, but there is nothing around the garter spring, and all in all there sure isn't what I would call a thorough coating of oil anywhere on the seal.

So my question is should I pull the seal and replace it? What exactly will happen if I run it the way it is? I'm not too keen on burning up a brand new top end, and if replacing the seal is the answer, then I can do that no problem. Interestingly enough, the seal I removed (installed in the factory) was as dry as a desert.

Thanks in advance for any help!
 
I don't think you need to do anything either... BUT... if you're REALLY worried, shlep a little bit of 2-cycle oil (or mix, honestly) into the bottom end and tip the saw on its side... it should get past the bearings and onto the seal. Ultimately, the whole bottom end is lubed by the oil in the mix, including the seals.
 
Thanks for the replies and help! I just took a dropper of Stihl Ultra and emptied it slowly into the PTO side crank bearing, and it seemed to disappear rather quickly. It comes back out slowly when I flip the crankcase to almost upside down. I inspected around the lip of the seal and just lightly touched it with a mini screwdriver, and it seems quite wet with oil. Of course, there's no way to know for sure if the oil is getting through to the rear of the seal.
 
I've made that mistake a time or two, but that's not as detrimental as a dry start on a lower rod bearing. Lol
When a puff of white smoke comes out of the exhaust followed by a screeching halt of the engine, it sticks in your mind from then on.
Anyway, with the unoiled seal; what I did was pull about 20 lbs of vacuum on the crankcase, then oiled the outer lip's circumference at the crankshaft.
Then I took a super thin gauge feeler gauge, and carefully lifted the pliable outer lip, allowing it to suck in some oil. They are resilient enough as long as you are careful not to nick the seal.

Although it worked, if I were you and I had more seals easily available, I'd opt for replacing them.
With me, it would latently "OCD on my mind", like a scratch on a new expensive paint job.... lol
 
No idea on the dry install, but you could put oil in the case and pressurize it. Conceivably, if you lie it on one side at a time, you could push some oil out of the seal without ruining them. Then rinse out the case with some mix.
 
Some years ago I was having a "chin wag " with a bike 2T engine tuner of some repute, & I said I used to oil crank seals with bar oil as it was tacky & I thought it would stay in place a little longer I gave him a small amount to try, & he came back a came back a couple of months later to say he was now using it on all his bottom end builds, so Iv'e continued to do the same I don't know if it is good or otherwise but the 2 of us have had no problems .
 
So would a dry seal simply be at higher risk for burning up before it receives oil via the mix (after which it should be fine)? I would imagine that any lubrication that's applied to the seal during installation would only last so long under the friction and heat generated by the seal's contact with the crankshaft, and thus the seal's lubrication needs to be constantly replenished via the mix. Correct?
 
Correct.
A seal on a chainsaw usually will fail under vacuum before it will under pressure.
If you don't have compressed air or a vacuum tester, just lift up the seal lip and let some oil flow into the seal.
 
Would slipping 2-stroke oil in behind the seal via injecting it through the PTO-side crank bearing work, as well, to sufficiently lube the seal? I don't currently have the top end installed, so there's no chance of creating a pressure/vacuum situation in the crankcase.
 
Would slipping 2-stroke oil in behind the seal via injecting it through the PTO-side crank bearing work, as well, to sufficiently lube the seal? I don't currently have the top end installed, so there's no chance of creating a pressure/vacuum situation in the crankcase.

Just drop a bit of two stroke oil in thru the open bearings and forget about it.

Unless you plan to dismantle your saw every time you run it how do you think the seal sees oil but thru the bearing. Some manufacturers in days gone by (Stihl being one) left metal shields in the bearings that would seem to severely limit oil to the seals. Bearings would go bad long before seals would fail. Old seals are worse.

Chris B.
 
Well, an unfortunate thing just happened. I noticed that the seal was sitting just a bit too high above the case (probably only about 1mm or so), so I decided to knock it down just a wee bit until it was flush. My heavy-hammer-hand knocked it down a bit, alright: all the way to the darn crank bearing. So, it looks like it has to come out after all. But, on the brighter side of things, this time I won't forget to grease it!

Thanks a bunch for all the help, folks! I really appreciate it!
 
I've made that mistake a time or two, but that's not as detrimental as a dry start on a lower rod bearing. Lol
When a puff of white smoke comes out of the exhaust followed by a screeching halt of the engine, it sticks in your mind from then on.
Anyway, with the unoiled seal; what I did was pull about 20 lbs of vacuum on the crankcase, then oiled the outer lip's circumference at the crankshaft.
Then I took a super thin gauge feeler gauge, and carefully lifted the pliable outer lip, allowing it to suck in some oil. They are resilient enough as long as you are careful not to nick the seal.

Although it worked, if I were you and I had more seals easily available, I'd opt for replacing them.
With me, it would latently "OCD on my mind", like a scratch on a new expensive paint job.... lol
novel approach
 
Well, an unfortunate thing just happened. I noticed that the seal was sitting just a bit too high above the case (probably only about 1mm or so), so I decided to knock it down just a wee bit until it was flush. My heavy-hammer-hand knocked it down a bit, alright: all the way to the darn crank bearing. So, it looks like it has to come out after all. But, on the brighter side of things, this time I won't forget to grease it!

Thanks a bunch for all the help, folks! I really appreciate it!
I just did the same thing to an 036. I thought the seal was a little proud so I tapped it around 10pm... ugh. Too tired to focus and drove it in too far. Luckily I have about 25 AM seals for this model.
 
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