The Harley Hummer Club

I have put a new set of rings in my 1956st engine. I rebuilt the complete engine last winter and had to take it apart again to check crankshaft hence new rings now. My problem now is that the engine will not start. It has spark and gas and seems to have compression ( I haven’t actually checked it with guage yet). But it won’t even pop when I prime it with gas. I have checked timing. But engine will not fire. Any ideas would be awesome!! Thanks!!

If the cylinder is getting gas, a hot spark, good compression and the timing is correct I can't think of any reason it should not start. Have you tried spraying some starting fluid into the carb before kicking it?

I've had this same problem with various 2 stroke engines over the years. When everything else is good then it comes down to the crankshaft seals being bad... or good seals and worn crankshaft areas where they seal. This throws off the air/fuel mixture ratio. Using old O.E.M. seals also isn't a good idea as most of them are just that... old. If they work they usually won't work for very long. I read in a post a while ago that Mutt found a source for metric seals that are good replacements. You might want to reach out to him if you find you need them.

Whenever I am faced with a situation like yours, I go back over everything. Clear your mind of the motor not wanting to start by doing some other task, wash the car(s), read a comic book, go to a junkyard… clear your mind.
Don’t assume (yea, you know) you have done everything correct. Go over everything because something was missed.
If you have gas and air at the correct ratio, good compression and spark at the correct time, physics dictates the motor should run.
Every motor has their own personality which we as their owners, need to learn.

After reassembling you may have flooded the motor in your excitement to hear it run again.
Good Luck

Thanks for the tips and thoughts. I’ll definitely look into seals and also give the whole process a restart. What should my compression be on an engine that the rings haven’t seated in yet?

I just put a compression guage on my engine and kicked it over. 55psi is what I get and 60 if I put a few drops of oil on piston. So much for my good compression thought. What should a 165st with new rings have for compression before the rings are seated. Thanks

I have been thinking about this because I rebuilt my engine last winter but still haven't run it yet and I may need to know that. To calculate what it should be you need to know the compression ratio which I don't know and multiply that by atmospheric pressure.I found that online as compression to psi calculator.If you have a head and measure the combustion chamber volume you can calculate the compression ratio with engine displacement and the head volume. Online examples I found : CR 6.5 is 95 PSI 8 is 117 and CR 10 is 146.
So if you are measuring 60 Pounds psi CR is 4. Seems low . Just thinking!

I dont' know the dimensions, but if you do know them, the compression ratio can be calculated.

http://www.torqsoft.net/compression-ratio.html

90 psi is good. 50 is not. compression ratio for 1948-61 models is 6:1

I have decided to tear my engine apart again. I’m looking for someone who could rebuild my crank and also for a new piston and a cylinder honed to match it. It’s a 1956st engine. Thanks