Being paranoid...

cbradio

Member
So, I rebuild my 8N again, after smoking bearings in two hours. Also had the oil pump rebuilt. with 10w40 in the engine, i get 50+ psi at start up and around 10 psi-30 psi from 0-100% throttle when warm.

I am paranoid that the 10 psi at idle is too low and I have installed the bearings wrong/dirty/bad etc and they are smoked again.

If the oil pressure stays consistent and doesn't get progressively worse is that within acceptable range? Could the cam or cam journals have excessive wear and cause a big 'warm drop'?

Thanks,

Cam
 
We have a 39 9N that we rebuilt the engine in and with 15-40 oil and operating temperature idling at 450 RPMs is 10PSI and at 3/4 throttle is 40PSI.

Mark
 
cool, thanks. after having to tear it down twice in 6 months, im a VERY nervous mechanic/parent about oil pressure and bearings.
 
while higher is better.

I'd say 6 psi per 1000 rpm is enough to keep elbows from bumping.

surprised it is as low as 10 hot idle if you did indeed have the oil pump serviced though..
 
The problem with rebuilding the pumps is you are using the old housing and it has wear. From what I have read the 9N was supposed to run between 15 and 30 psi new depending on oil and temperature. Although I haven't found anything in writing I believe that is why they stepped up to the 3/4 inch gears.

Mark
 
You need a new pump body to go to the 3/4 gears which means you have to have the engine line bored because the pump is part of the front main bearing cap. Many people rebuilding these engines can only afford to do so much.

Mark
 
I realiza all that.

i can't imagine going to the labor to rebuild and engine and come out with 10psi oil pressure.

that was my point.

I've done po-boy rebuilds with hand lapped valves, new rings, reaming and new main and rod bearings. all stuff you can do in an afternoon. slap pan and head gaskets on and go. but all those machines held hot idle oil pressures in the 20's at least. and cold throttle in the 40's..

If I tore one down with 10 psi.. i think I'd have to have oil pump work done unless i just needed it to work another month or so .

repalcing a crank will get spendy if you let them go. no need to rebuild twice if it is done correctly once... anbd a rebuild with bad oil pressure is depressing..
 
I guess we'll have to agree to disagree because I still Know that 10 psi on a hot engine at 450 rpms will run for many years as long as it increases as soon as you start to rev the engine and this is from experience rebuilding many N series engines and never had a failure.

Mark
 
either you didn't read my posts in entirety, or you didn't understand them.

I never said they wouldn't run. even said that you SHOULD be fine at 6 psi per 1k rpm.

I was pointing out that a rebuild ( labor and any $ invested ) would be disapointing on a machine with 10 psi, if it did not also address the pump. Disapointing does not mean it won't work.
 
If I rebuilt an overhead valve engine and only had 10 psi I would take it back apart and find out why but on an N it is a different story. If replacing the pump was easy I would do it every time as I do on the overhead valve engines. I am not disappointed with 10 psi at 450 rpm and operating temp especially when it is 30 psi by 12 - 1500 rpm and 40 psi beyond that.

Mark
 
I won't continue to debate you, ..if you like 10 psi idle oil pressure on a rebuilt engine.. that's your thing.

they simply CAN be rebuilt to new specs and have good oil pressure at hot idle. excess pressure can be dimped out the relief at operating rpm.. and still have good pressure at idle.

again. if you want it and chase it.,
 
I never said they couldn't be made better. I said many people have financial restrictions on how much they can do I'm fine with you having your opinion and I'll continue to have mine. I must say I enjoyed the debate and respect your opinion even when I don't completely agree.

Thanks

Mark
 
yep. when you aren't flowing enough oil to keep some hydrodynamic film pressure up.. then metal bumps..

ps.. have you verified that gauges readings?
 

I would replace that gage ($12) before I'd draw any conclusions from it!
At least remove the oil line from the governor and, see what the oil pumps like!

Joe
 
(quoted from post at 15:43:03 04/11/14) I guess we'll have to agree to disagree because I still Know that 10 psi on a hot engine at 450 rpms will run for many years as long as it increases as soon as you start to rev the engine and this is from experience rebuilding many N series engines and never had a failure.

Mark

An N-series flathead has no overhead lubrication to deal with so all you need in the way of oil pressure is enough to keep the journal bearing oil clearances filled and produce a decent cylinder wall spray. Pump oil pressure is NOT what keeps the journal off the bearing but it is what makes the spray.

Of course oil pressure decreases with increased oil clearances so if you start out with new clearances and 10 PSI pump pressure at 1500 RPM you can/should expect a decreased service life from the engine.

AFAIK my 51 8N has never been apart and it produces just a few PSI short of 30 PSI at hot idle. The 3/4" gears are a 19% increase in oil pump displacement which is significant.

TOH
 

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