Off topic: Need 2 stroke help!

[93Bandit]

Hey guys, first off sorry if this is the wrong area to post this question. I need help and was worried if I posted this elsewhere it wouldn't be seen. Please move the thread if this is inappropriate.

I've got a 2 stroke concrete saw (Basically same as a chainsaw) that won't start. Backstory, it's only a few years old but engine got dusted during use and ruined. I completely rebuilt it, new jug, rotating assembly, gaskets, seals and bearings, etc. Rebuilt the OEM carb and put on new rubber intakes. Basically the only thing I reused was the engine case and carb. After rebuild, started on the 2nd pull and ran great. Used a few times and then it sat for a few months. Well now it won't start, at all, plug is dry but machine is full of fuel. Checked spark, good. Poured a bit of fuel into cylinder through the spark plug hole, reinstalled plug and it fired briefly. OK, so seems like its not getting fuel for some reason. Maybe the fuel line got disconnected? I started disassembly to check fuel lines and carb, but as I was taking it apart I noticed one crank seal was blown out of the case, resting on the crank behind the clutch. I checked the other seal behind the flywheel and it looks fine, fully seated into the case. Hmmmm. I'm not a 2 stroke expert but I know the crank case must be sealed to run properly because crank case pressure and vacuum is used to pulse the carb fuel pump as well as charge the cylinder with air/fuel.

So here's my question, I know a leaking/bad crank seal can cause irratic idle and/or cause it to die, and/or over Rev. But, can a crank seal that has completely blow out prevent the engine from starting? I'm wondering if the lack of crank seal is preventing the fuel pump from working? If this is true, wouldn't using the primer bulb charge the cylinder with enough fuel to fire at least once? Or could that massive crank case leak even prevent it from firing even if primed, due to the lean condition caused by the crank case leak ? I guess I'm just concerned because i wouldn't think a blown crank seal would completely disable the machine, but maybe it can?

What do you guys think? Any help is appreciated!

 

[Grimly]

For sure, a crank seal blown out of position will prevent the fuel/air mix being transferred.

 

[rphillips]

And, I'm pretty sure, the primer bulb doesn't send fuel into the cyl. Thinking that bulb assures the carb system is completely primed.

 

[93Bandit]

For sure, a crank seal blown out of position will prevent the fuel/air mix being transferred.

Thank you for the confirmation!

 

[93Bandit]

And, I'm pretty sure, the primer bulb doesn't send fuel into the cyl. Thinking that bulb assures the carb system is completely primed.

I think you're right. After I made my post, I thought about it further and realized the primer just makes sure the carb is primed. So it still needs crank case pressure to pull fuel into the cylinder.

 

[93Bandit]

I ordered a new seal so I'll let you guys know if that fixes it.

Now the greater question is, why did the seal blow out? I know it was pressed in fully when I installed it, and it took some force to drive it in so I don't think it was undersized. It was an OEM part. Hmm.

 

[Grimly]

I ordered a new seal so I'll let you guys know if that fixes it.

Now the greater question is, why did the seal blow out? I know it was pressed in fully when I installed it, and it took some force to drive it in so I don't think it was undersized. It was an OEM part. Hmm.

What was the crank end float like? I'm thinking the seal may have walked out.

 

[93Bandit]

What was the crank end float like? I'm thinking the seal may have walked out.

I thought about that but there's no perceiveable crank end float. Maybe it was a faulty seal, or maybe I didn't get it fully seated as I thought.

The only other thing I can think of is if the crank case got overpressurized somehow. Idk if it could backfire all the way into the crank case?

 

[Grimly]

The only other thing I can think of is if the crank case got overpressurized somehow. Idk if it could backfire all the way into the crank case?

It's not something I've had happen so can't say for sure it wouldn't happen that way, and it's about the only source of a massive overpressure event I can think of. Also worth checking the ignition timing in case it's slipped.

 

[93Bandit]

It's not something I've had happen so can't say for sure it wouldn't happen that way, and it's about the only source of a massive overpressure event I can think of. Also worth checking the ignition timing in case it's slipped.

Ignition timing is determined by the flywheel clocking on the crank, which is keyed. So it can't slip without the key snapping off. It's in good shape so Ignition should be fine. Idk what else to do. I ordered an extra seal, so I'm going to install the new one when it arrives and see how it goes.

 

[dorkburger]

Interested to hear the result. I had a 15 year old leaf blower (Echo) that was stone reliable until it just quit. It had spark, compression, but the plug was either bone dry or soaked. After much trouble and nearly burning the garage down by drying the plug with a torch, I figured carb, and bought a cheap replacement. Same result. After searching countless YouTube videos, I found one- and only one- pointing out spark timing. That was my issue. The keyslot on the flywheel was damaged. A temporary fix bought another season. Last summer it died again and I'd had enough. To the curb....The thing that really annoyed me was that I had a good running extra that was a trash night salvage that I had thrown away the year before to save space in the shed...

 

[93Bandit]

Interested to hear the result. I had a 15 year old leaf blower (Echo) that was stone reliable until it just quit. It had spark, compression, but the plug was either bone dry or soaked. After much trouble and nearly burning the garage down by drying the plug with a torch, I figured carb, and bought a cheap replacement. Same result. After searching countless YouTube videos, I found one- and only one- pointing out spark timing. That was my issue. The keyslot on the flywheel was damaged. A temporary fix bought another season. Last summer it died again and I'd had enough. To the curb....The thing that really annoyed me was that I had a good running extra that was a trash night salvage that I had thrown away the year before to save space in the shed...

Yeah I checked the keyslot and flywheel and all is well. That's disappointing, I've done things like that as well. I'm a bit of a hoarder for that exact reason. I pickup anything with a small engine from the side of the road and fix it, then they pile up in my shed. I've recently started selling/giving them away. Trying break bad habits and get rid of stuff. Also why I sold all my bikes, except my 850L. Hard to enjoy any of it when you have too much and none run.

 

[Michael Graziosi]

If the engine is still together, can you do a compression test? If so, be certain to perform it with the throttle wide open. I have no idea what the psi spec would be for a small engine, but I would think it should be at least 100 psi. If it's low, then the crank seals are likely leaking assuming that the piston and rings are good.

 

[93Bandit]

If the engine is still together, can you do a compression test? If so, be certain to perform it with the throttle wide open. I have no idea what the psi spec would be for a small engine, but I would think it should be at least 100 psi. If it's low, then the crank seals are likely leaking assuming that the piston and rings are good.

I didn't do a compression test, but it is fine by feel. The engine has a brand new jug, piston, rings crank etc, and it is difficult to pull with the compression release closed.

Per the factory manual, the crank seals are supposed to be pressed into the case without an adhesive, but I'm wondering if maybe I should smear a very small amount of RTV on the outside of the seal before pressing it in. What do you guys think? It's such a small engine and tight space to work in and the seal is incredibly close to the crank bearings, I do not like the risk of potentially contaminating the bearing/crank case with RTV. I ordered 2 seals, so maybe I'll just press this one in and if it pops out again I'll RTV the second seal before installing it?

I don't like running the saw with the chance of the seal popping out. Concrete saw runs in very dusty harsh conditions and I do not want it sucking in concrete dust through the crank seal. This saw consumed a ton of concrete dust which is why I rebuilt it in the first place.

 

[Michael Graziosi]

I would think that the majority of the sealing is from inside of the seal on the crank. The press fit of the seal into the case should be enough. If the previous seal popped out, maybe it was slightly cocked and not completely seated and/or some slight damage either to the outer portion of the seal or the case. RTV silicone may not have much adhesive effect. I don't recall the name of the stuff but years ago Permatex had a gasket maker product. It was a brown liquid and a bit tacky. It worked great but a beast to clean, especially if removing the stuff after disassembly. There's so many different gasket products at the auto stores today. Maybe a visit to one that the counter/cashier people actually know what they are talking about and can offer some advice on a "tacky" gasket maker product.

 

[93Bandit]

I'm leaning towards it being installation issue or maybe slightly out of spec seal. I'm going install the new one without any sealer or adhesive. The concern I have with putting anything on it before install is it's a maintenance part so will need replaced again in the future. It'll be nearly impossible to clean the mating surfaces in the future without tearing the whole bottom end apart which is not ideal. Supposed to be able to just pull the old seal out and press the new one in so I'll try it that way one more time.

 

[93Bandit]

It's fixed!!!!

I pressed in a new seal with no sealant/adhesive. It drove in pretty snug so I'm thinking I installed the previous seal incorrectly or the seal itself was defective. Either way, with new seal pressed in and no other repairs made, it fired right up and runs great.

Thanks for the help guys!

 

[rphillips]

Probably something just didn't fit exact or go in exactly right. Sounds good now, would be completely confident after the 3rd. use. Great to hear it's looking good.