# Crank Seal



## theoldwizard1 (Oct 4, 2020)

The definitive test for a crank seal is a pressure/vacuum test. This is a pain, because you need block off plates for both the intake (carburetor) and the exhaust (muffler) and a pressure/vacuum source.

Short of "visual inspection" _("Hmmm, there is a lot of oil and dirt build up that looks like it is coming from behind the flywheel" and "It's over 10 years old, I'll bet it need a new crank seal")_ is there any other method to assess the "quality" of a seal ?


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## Maintenance supervisor (Oct 4, 2020)

Smoke test, block exhaust and pack puddy or play dough around the carb/ choke,insert straw . Light up a cigar and blow smoke down the carburetor. Should come out at any leak point including casting defects.


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## theoldwizard1 (Oct 5, 2020)

Not a smoker, but if I get in this situation again I might have to start !

*An tips to installing the seal ? I plan on using a socket as a seal driver and will lube the crankshaft first. Do I need any RTV on the out side of the seal ?*


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## Maintenance supervisor (Oct 5, 2020)

I haven't resorted to rtv but inspect the bore for bad nicks, then its recommended. 
I put a couple of wraps of electric tape on any part of the crank shaft that is stepped, to keep the seal from grabbing it, just lube the seals rubber flange with grease. 
I use a nice stainless steel washer under the socket so I get full contact on the seal.


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## lone wolf (Oct 5, 2020)

theoldwizard1 said:


> Not a smoker, but if I get in this situation again I might have to start !
> 
> *An tips to installing the seal ? I plan on using a socket as a seal driver and will lube the crankshaft first. Do I need any RTV on the out side of the seal ?*


Dont use a big hammer use a light little one and dont let it get out of square as you tap it in ,correct it with little taps if not straight ,then drive it in. A sealer around the rim will help, I like Locktite it gets in better because its thinner.


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## theoldwizard1 (Oct 6, 2020)

Maintenance supervisor said:


> I put a couple of wraps of electric tape on any part of the crank shaft that is stepped, to keep the seal from grabbing it, just lube the seals rubber flange with grease.
> I use a nice stainless steel washer under the socket so I get full contact on the seal.


I will have to remember those tricks !


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## theoldwizard1 (Oct 6, 2020)

I have to install a new rubber hand grip before reassembly. That took twice as long as installing the seal !

The seal went in no problem using a socket, but the washer trick would have done a better job of getting it to bottom out evenly. I did not need the electrical tape as I used Fluid Film for lube on the seal.

It started and ran well (always did) ! Stored with about 1/2 tank of fuel. We will see if there is a stain on the floor tomorrow.

Last question for this thread. *Crank seals are a wear item. SWAG How long do the last for typical home owner usage ?*


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## Maintenance supervisor (Oct 6, 2020)

Hahs , some a couple years , others 40years. So recommended replacing every 2 ,I think but if installing high quality seals maybe your lifetime?


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## theoldwizard1 (Oct 6, 2020)

Maintenance supervisor said:


> Hahs , some a couple years , others 40years. So recommended replacing every 2 ,I think but if installing high quality seals maybe your lifetime?


OEM. $8 I'll probably go longer than 2 years. The quick check is to pull the starter rewind assembly (3 screws). If there is a lot of oily dirt, it is time for a new seal.


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## Maintenance supervisor (Oct 6, 2020)

A good check for me , is to spray the area with non- chlorinated brake cleaner(green can). If the saw is sucking air at idle the brake cleaner will almost immediately kill the saw running. Pressure test is the more scientific way. 
Easy to hit the clutch side a little bit more difficult to get the flywheel side.


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## sean donato (Oct 6, 2020)

I have saws that are older then me with original crank seals. My grandpas stihl 031av (that he bought new) has never even been apart. My lancaster 60, mac 10-10a, pm605, all original seals and run just fine. None of them.get used hard anymore, but all run with no issues. Even my daily go to saws have years on the seals. I don't think its necessarily a time issue. So much as a bearing starting to go out, or another issue. Crank seals (for me) havent ever just given up the ghost for no reason, and age typically hasn't been one of those reasons (again for me) ymmv.


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## Maintenance supervisor (Oct 7, 2020)

Yeah, heat ,debris and poor lubrication wil definitely lead to failure.


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