Hi was wondering i have 1340 evo screaming eagle heads pistons 10.5 1 compression ev57 cam. screaming eagle coil, module the bike was idling and i noticed alot of pressure coming out of the front exhaust and alot less coming out of the rear exhaust.I am assuming they should be the same?I want to do a compression test on the cylinders what kind of readings should i be looking to get?Thx for the help

 

I would say 170 range give or take. Mine is similiar with 175 and 180. Unless both cylinders are extremely low the main thing is to make sure they are within range of each other. Some manuals say they need to be within 10 pounds difference and some say within 10% of each other.

 

Just wondering is there any thing else that would cause the rear exhaust pressure @ idle to be alot less than front?

 

Is the bike running Ok? Does it pull fine through the gears? It might just be the the rhythm of the engine making it feel as if the rear is moving less air. If it is low on the rear cylinder there are several things that could cause a compression loss. Bad or burnt valve, damaged or worn ring, scored cylinder walls, ETC.

I helped my friend rebuild his 76 shovel over the winter and it ran fine but was weak. Checked the compressioin and it was 90 front 60 rear. Pulled the jugs and there was a huge scar on the rear cylinder.

 

seems to run fine i wouldnt have even noticed but i was just standing behind the exhaust when i noticed the difference in the exhaust pressure.I will do a compression test to see i hope its nothing major as the motor only has 15,000 km after i did the heads and pistons.may have to do it again damn

 

Warm the engine up, take the plugs out, ground out the plug wires, lock the throttle open and crank it ver looking at the gauge. It should reach top numbers after about three revolutions, if it takes more your rings or valves may be weak. put some oil in the cylinders and see if the pressure goes up. If so your rings may be going.
You may also want to do a leakdown test. Don't forget to check the valve adjustment as mis-adjusted pushrods can also vary cylinder pressures. Different lengths and bends will cause different exhaust pressures. A weak spark will give incomplete combustion resulting in weak exhaust pulses, however this usually can be felt while driving. Hope this helps.

 

a bud is getting me compression guage so i will do on the weekend thanks for all the help