8n running rough

[michaelthorne75]

I had a previous post about my 51 8n running rough. So after doing
all that could on the ignition and the carburetor, I checked
compression. Reading about 90 on dry and about the same on wet
test. This is a newly rebuilt engine. I would have thought the psi
would be higher on a new rebuild.

So my question is , is it possible that all the valves are not adjusted
correctly and could that be the cause of it running rough.



It starts and runs but sounds somewhat rough. Won't idle below 600
rpm or it wants to cut off due to the rough idle.

Thanks.

 

[Steve A W]

How "new" of a rebuild?
Could it be the rings have not seated yet?

 

[michaelthorne75]

The engine has about 15 min of run time since rebuild.
Could the rings not seating be the issue ?

 

[R Geiger]

(quoted from post at 14:42:08 11/03/17) I had a previous post about my 51 8n running rough. So after doing
all that could on the ignition and the carburetor, I checked
compression. Reading about 90 on dry and about the same on wet
test. This is a newly rebuilt engine. I would have thought the psi
would be higher on a new rebuild.

So my question is , is it possible that all the valves are not adjusted
correctly and could that be the cause of it running rough.



It starts and runs but sounds somewhat rough. Won't idle below 600
rpm or it wants to cut off due to the rough idle.

Thanks.

I would readjust the valves before i got too excited about other things, if you have good spark and a well adjusted carb. hope you have adjustable lifters installed.

 

[michaelthorne75]

Ok. Thanks. Yes the are adjustable lifters. I adjusted them per the
manual before during rebuild. But I will check again. Is this normal
for them to need adjusting again ?

Thanks

 

[Dell (WA)]

Mike.......good rebuilt N-engine shuld compression test +150-psi. 15-mins is NOT enuff run time to seat the rings. I'm gonna guess you checked ring end gap and staggered them around the piston. Hope you used the BETTER 3-ring pistons vs the 4-ring oil burners.......Dell

 

[michaelthorne75]

Dell. Yes I used the 3 ring and staggered them. Sorry for sounding so stupid. I didn't realize that it took a while for the rings to seat.

Would this have anything to do with engine sounding rough?

Thanks for the help

 

[R Geiger]

(quoted from post at 15:35:21 11/03/17) Dell. Yes I used the 3 ring and staggered them. Sorry for sounding so stupid. I didn't realize that it took a while for the rings to seat.

Would this have anything to do with engine sounding rough?

Thanks for the help

lot of engine out there with 90 psi that do not run rough unless you are fouling spark plugs. assume you have double checked firing order?

 

[michaelthorne75]

Yes. I have done everything I can think of. It's a 6v system. I have
checked timing , points , coil ,carburetor etc. just can't figure out why
it's running rough. It's not real bad , just more noticeable at idle.
Only thing I haven't checked again is the valve adjustment.

 

[Den N Ms]

michaelthorne75,Vacuum leaks or a rich fuel mixture @ idle will cause a rough idle.You might want to check it for vacuum leaks (manifold gasket,carb mount gasket,warped flange or even a manifold with a hole in it.Vacuum with a gauge hooked to the manifold should be around 19.7 IN HG at a idle.Check for leaks by spraying WD40 or such around manifold ports and carb mount.Compression is 120 lbs. tops @ sea level on a new rebuild not 150#.

 

[Dell (WA)]

Den.......was just guessing on compression. Think my Dodge Cummins Diesel is close to 200#.........Dell

 

[boler76]

did you put new seals on the carb throttle shaft?

 

[michaelthorne75]

Yes. But it doesn't seat very well. Maybe I can put some grease on it to help seal.