Engine Trouble Recently Rebuilt engine won't start

[crassius]

the other half of builtin bearing seal is INSIDE the case

sorry about that - got confused running into shop from doing a repair outside - obviously, a seal inside would prevent lube from fuel mix from preserving bearing

will need to think more on this tonite to see why bad seal always reads about 25 - 30#

 

[gary55]

No it's not. And it's leaking like a sieve.

 

[crassius]

something different about your motor

I get a no-start bike in, I check spark and hook up gauge, I get on bike and peddle the crap out of it and get 30#, I open covers and replace whichever seal is just hanging off end of crank, I peddle bike and get 120# or more and it runs with plug back in.

that's how it goes here all the time

I see you have sealed bearings on crank - that may be what's holding pressure for you while they are still new.

 

[crassius]

just had a thought - sometimes the 4 screws for stator are drilled all the way into case and I have to put washers under stator to get a good seal - did you check that on your cases?

 

[gary55]

Were their nothing at all under the piston and cylinder. Completely open with nothing but atmospheric pressure to draw from. We'll give a meager 6 to 1 ratio at sea level you would have 88.2 lbs. compression. The compression is by far more based on the atmospheric pressure and how many times the atmospheric pressure is compressed above it's existing unit after the exhaust is closed. You are multiplying 14.7 lbs. by 6. Sealed not sealed 14.7=1 compressed at 6 to 1 has little choice in this universe to physically be anything other than 6X14.7.

 

[crassius]

that all makes sense, but there seems to be something else going on, some factor of how all the parts work together that changes things somehow

 

[Frankenstein]

What about the exhaust port being open to standard local atmospheric pressure and being the last part to be closed off? Unless there's significant back pressure why isn't most of the pre-pressured air not just excaping? Unless it has something to do with the speed at which one turns the engine over? Gary are you using a drill to spin it? That engine isn't mounted in anything and at your age I don't think you're cranking it over with a box wrench.

 

[crassius]

I'm also wondering if blown seal prevents fuel entering so maybe dry rings in a somewhat worn motor would cause that 30# reading - just don't know, but see it many times.

 

[crassius]

I'm wondering now if there are enough guys here who work on these to report if a blown seal reads that low for them, and is that reading only on motors that have no extra seal built into the mains.

seems this would be good info to have

 

[Frankenstein]

I'm also wondering if blown seal prevents fuel entering so maybe dry rings in a somewhat worn motor would cause that 30# reading - just don't know, but see it many times.

I wonder if the design of the pressure gauge would have anything to do with it, probably not.. I'd say someone needs to test it with a non-shielded bearing VS shielded. I no longer have a complete engine laying around that has movable parts in it..