Case Colt Ingersoll Tractors banner
1 - 4 of 4 Posts

·
Registered
Joined
·
40 Posts
Discussion Starter · #1 ·
Can anybody help me with suggestions as to what might be the cause of all the pressure when I pull the dipstick with the engine running. I was told to check this to see if the engine was in good or poor condition. Also while engine in low idle it won't stop hunting. This is a 1974 Case 446 with 16hp Onan. Any help is greatly appreciated. Thanks
 

·
Ingersoll Dealer
Joined
·
4,265 Posts
Not sure who suggested you do that ... but I suspect not knowledgeable Onan or boxer twin owners.

This is not like a car engine which has 4, 6 or 8 balanced cylinders. The boxer twin pushes both pistons out and then pulls them both in. Horizontally opposed, or 'boxer' configuration.

Similar to a single cylinder, that's a huge displacement of air in the crankcase every cycle and it results in major pressure pulsations. There is a reason the dipstick on an Onan has a seal and a detent (of sorts) to keep the oil and dipstick in the engine.

During normal operation the breather system keeps all this pulsation under orderly control ... pull the dipstick and you will for sure get pressure pulsing and even can end up with an oil bath. By pulling the dipstick, you let it suck a massive amount of air down the dipstick tube ... and its coming right back out on the return stroke.

I suspect your adviser was thinking of an old idea that extra air would get by the rings if the engine has poor compression ... just not a good test in this configuration of engine (and maybe not at all).

Want to check that condition? The Onans respond perfectly well to a compression gage. An engine with near equal compression on both sides, at 80PSI or higher, is in OK shape. The higher the better, with new likely in the range of 120-130.

Brian
 

·
Onan Master, new and used parts.
Joined
·
1,509 Posts
dr
brian is correct, NEVER pull the dipstick on a running onan engine.

as to the hunting, check your carbsettings.
low speed (on your left when you are in the seat) 1 turn initial.
main jet on the right 1 1/4 to 1 3/8 initial.
also check for loose governor linkage.
good luck. boomer (the used onan engine parts guy)
 

·
Registered
Joined
·
40 Posts
Discussion Starter · #4 ·
Thanks very much guys for the advice and tips. I just talked to another mechanic who is a really good friend of the family who collects garden tractors and has loads of experience with the Onan engines aswell as many others. He said the exact same thing about the Onan engines. And advised me that the engine was in good shape and the carb needed adjustment and the points and condenser might need to be checked and maybe replaced. It doesn't smoke at all and he said he would stop by when he gets time and do a leak down test to make sure the compression was good. I'm super excited right now cause I had it running and driving for over 30 minutes. It spits and chugs once in a while but hopefully I can get that sorted out shortly. The gentleman who I'm buying it off of let me have it for 3 weeks to see if it ran good and if I was satisfied to come back and pay him for it which was awesome of him. Thanks again guys!!!
 
1 - 4 of 4 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top