Board index Flathead Power-Technical Questions, Answers, and Suggestions K-Models Crank compression on 52 Model K.

Crank compression on 52 Model K.

Moderators: Curt!, Pa

Post Mon May 15, 2006 5:29 pm

Posts: 328
Location: north central Ma.
Pulled the plugs tonight after 7 days of rain i had to do something out the in shop.
As you might recall my 52 smokes on start up and lightly while running and is using 1/2 quart per 100 miles sometimes more.

Plugs look better then i though both are evenly colored.

Tried my leak down tested but can't seem to keep the motor from rolling over in gear, brakes locked you get to 60psi and she moves. ERRRR.........

Got out the old compression tester and opened the throttle fully kicked away.......
Front cyl 70psi
Rear cyl 77psi

Seems low but it's a flat head Is this in the right range?

Thanks for the help.

44dwarf
"Smok'in the competition NOT Tobacco"
"Transplant organs, Don't bury them!"
Why dwarf? 5/8 scale race cars! http://www.dwarfcarracing.com

Post Tue May 16, 2006 5:45 am

Posts: 1050
Location: Greenbackville, Virginia, USA
44dwarf, compression should be 90psi +. Engine hot? Did you try squirting some oil into the cylinder/piston area to check if it's the rings? My KH would give 90 psi even with poor sealing rings. Yes a leak down is an SOB to do on a K type, damn engine just wants to turn over. G 8)

Post Tue May 16, 2006 10:01 am

Posts: 328
Location: north central Ma.
Too much rain to warm it up. I wanted to take it cold and hot to compare. Will do hot when the water level drops. Got the bike up on a pallet now............
Noah build me an Ark!

44dwarf
Last edited by 44dwarf on Tue May 16, 2006 10:59 am, edited 1 time in total.
"Smok'in the competition NOT Tobacco"
"Transplant organs, Don't bury them!"
Why dwarf? 5/8 scale race cars! http://www.dwarfcarracing.com

Post Tue May 16, 2006 10:36 am
panic

"If atmospheric pressure is 14.7 lbs psi....then 6:1 should be 88.2 and 5:1 about 73.5 psi."

No, doesn't work that way.
1st: you can't capture the entire stroke length since the intake valve is still open ABDC.
2nd: the compression raises the temperature in the chamber, which increases the pressure. The theoretical effect (ratio of variable heats of the gas) is CR^1.4, but that's too high since some heat is lost back into the castings etc. The usual value is about 1.2 to 1.3 depending on the engine.
Read more: http://victorylibrary.com/tech/cam.htm

Post Wed May 17, 2006 6:15 pm

Posts: 328
Location: north central Ma.
An old timer freind say it has to be rings and that 52 was know for a crap oil control type ring. He also say i can pull the cyl off with the motor in the frame! Looks to me like theres not enough room. Anyone know for sure?
Can you pull the cylinders in the frame?

Thanks
44
"Smok'in the competition NOT Tobacco"
"Transplant organs, Don't bury them!"
Why dwarf? 5/8 scale race cars! http://www.dwarfcarracing.com

Post Thu May 18, 2006 7:27 am

Posts: 1050
Location: Greenbackville, Virginia, USA
44, yes you can remove the cylinders in the frame. Disconnect battery. Remove the gas tank. Top motor mount and heads. Carb. Intake manifold. Open the valve covers and back off the tappet adjustments all the way. Exhaust system off. Remove the generator. Rotate flywheels till pistons are at bottom of stroke and put the transmission in gear. Remove cylinders. Total time less than an hour to remove. Be carefull of crap (like broken rings, carbon, gasket pieces) falling into the cases! Re-assembly takes a lot longer. Have fun! (Been there, done that, don't envy you) G :wink:


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