MS460 air leak

[coredaus]

Patient is a 460, melted piston/cylinder. before disassembling top end, did a pressure test. the oil seal is leaking like an SOB, I'll replace.
Also noticed that air is leaking out of this screw hole (oil pump mount screw hole, clutch side). Is this normal, the screw just plugs this leak?? Just trying to avoid ripping open bottom end

 

[a. palmer jr.]

I guess you could use a little thread sealer when you put it back together..I don't see any reason to rip it apart.

 

[Philip Wheelock]

Suggest checking the crank bearings since a bad bearing can cause the oil seal to fail; if the saw's got lot of hours, it may be worthwhile to replace them anyway. Splitting the case is a pain, but the bearings and gaskets are cheap.
Place the small rubber 0-ring to the right of the crank in a safe place until re-assembly; they're easy to lose.
The service manual doesn't mention any special treatment of the oil pump screw hole you mentioned.

 

[gunnusmc03]

I don't recall if those oil mount holes are supposed to be blind or go through the case wall . The screw threads should seal it up though. It'd be easy enough to test, just thread in the screws and check for bubbles.

 

[Frogfarmer]

The screw hole will not be an issue. As stated above check the bearing and fit to the case if the seal is leaking alot.

 

[Definitive Dave]

That hole should be 4mm and not go through the case in my experience, in the picture it looks oversize (5mm), maybe a prior owner stripped the old hole and used a larger screw as a repair?
lots of good advise already in this thread specific to your question
dave

 

[Chainsaw Jim]

Hopefully that hole didn't get blown out when the pump was last installed. If so I would imagine there would have to be a chunk of magnesium floating around that has already passed through the system or is ready to.

 

[coredaus]

cool thanks for the responses. man this site is awesome, wealth of knowledge. I'll throw up some pics once I look into this more

 

[pioneerguy600]

460`s are notorious for spinning the bearings on the clutch side, have many case halves with spun bearing syndrome here, the bearing will feel good but it will spin in the case and it will cause a vac leak, the seal lip will wear unevenly.

 

[coredaus]

Split the case... The hole is blind, and 4mm as it should be. Found the issue, maybe.
looks like a crack, going all the way around the bearing seat. or not, is the bearing seat an inserted piece cast into housing?? can see the broken paint line all the way around.
whatchya'll think, this thing shot?
already have the new top end parts, would rebuild if it makes $ sense

 

[pioneerguy600]

I think you will find that crack will cause an air leak, I fixed one like that with Locktite 290 Green, it is a wicking type locker that I applied to a case I had cleaned thoroughly with acetone. With the engine built to the point I could do a vac test, all blockers in place applied vac while applying acetone to the damaged area, the vac drew it into the crankcase, let it sit for an hour and then applied the green Locktite to the damaged area again with vac pulled on the case, it drew the Locktite into the cracks, after applying a good amount of sealer I removed the vac and left a little sealer on the surface of the cracks. After 12 hours I completed the assembly of the saw, it held vac and is still running 5 years later.

 

[lone wolf]

I think you will find that crack will cause an air leak, I fixed one like that with Locktite 290 Green, it is a wicking type locker that I applied to a case I had cleaned thoroughly with acetone. With the entire built to the point I could do a vac test, all blockers in place applied vac while applying acetone to the damaged area, the vac drew it into the crankcase, let it sit for an hour and then applied the green Locktite to the damaged area again with vac pulled on the case, it drew the Locktite into the cracks, after applying a good amount of sealer I removed the vac and left a little sealer on the surface of the cracks. After 12 hours I completed the assembly of the saw, it held vac and is still running 5 years later.

Slick work there

 

[pioneerguy600]

Slick work there

All I can say is that it worked for me, the crankcase was still structurally sound, just had those cracks around the steel insert so I figured it would be worth a try.

 

[jackdaripper]

I think I may have this issue as well. @pioneerguy600 what were your symptoms? I've been going crazy trying to diagnose a major air leak that only shows up when it's running. Only hint that I have is that it is leaking air from the oiler screw hole like the OP. I split the case and replaced the bearings and seals, and I recall a strange crack or casting bevel exactly like the OP's picture.

 

[pioneerguy600]

I think I may have this issue as well. @pioneerguy600 what were your symptoms? I've been going crazy trying to diagnose a major air leak that only shows up when it's running. Only hint that I have is that it is leaking air from the oiler screw hole like the OP. I split the case and replaced the bearings and seals, and I recall a strange crack or casting bevel exactly like the OP's picture.

Every saw I rebuild gets a Vac and pressure test before teardown, the saw was straight gassed and needed cylinder cleanup and a new OEM piston. It failed its Vac and pressure test so I was looking for bad seals but found the leak at that point. The pocket for the bearing was still tight so I figured give the sealer a chance. I work on all different kinds of engines so the background of repair spans a wide assortment of engine build and repair. I live in an area of freeze and thaw and have seen many engines with cracked crankcases that we have fixed with sealers.

 

[jackdaripper]

Every saw I rebuild gets a Vac and pressure test before teardown, the saw was straight gassed and needed cylinder cleanup and a new OEM piston. It failed its Vac and pressure test so I was looking for bad seals but found the leak at that point. The pocket for the bearing was still tight so I figured give the sealer a chance. I work on all different kinds of engines so the background of repair spans a wide assortment of engine build and repair. I live in an area of freeze and thaw and have seen many engines with cracked crankcases that we have fixed with sealers.

Gotcha. If you can remember this particular one, did you split the case upon finding the leak and then see the crack like the OP's photo showed? And was the leak only coming through the screw hole?

 

[pioneerguy600]

Gotcha. If you can remember this particular one, did you split the case upon finding the leak and then see the crack like the OP's photo showed? And was the leak only coming through the screw hole?

I found the leak during the initial vac and pressure test, it was leaking around the steel insert that surrounds the bearing pocket, not the screw that retains the oil pump. The screw that retains the oil pump is a blind hole it does not leak normally.

 

[jackdaripper]

I found the leak during the initial vac and pressure test, it was leaking around the steel insert that surrounds the bearing pocket, not the screw that retains the oil pump. The screw that retains the oil pump is a blind hole it does not leak normally.

Ok, thank you. I think I'm going to heat up my case while doing pressure/vacuum testing and see if it begins to show the leak from around the steel insert. If so, I'll keep it hot with a heat gun and try your technique of sucking in green loctite under vacuum. I really appreciate your help.

 

[pioneerguy600]

Ok, thank you. I think I'm going to heat up my case while doing pressure/vacuum testing and see if it begins to show the leak from around the steel insert. If so, I'll keep it hot with a heat gun and try your technique of sucking in green loctite under vacuum. I really appreciate your help.

It has worked for me but I cannot guarantee it will work for everyone, getting all oil out of the crack before applying the Loctite is of great importance, nothing will stick to oily surfaces.