Lost engine oil pump prime

[astjp2]

Re: Lost engine oil pump prime

It can only be the pump, that is the only place for it to drain back from and not have enough residue to get it to prime on start. Let me repeat myself, its the pump/cavity, if you change the accessory case with a NEW ONE, you wont have that problem again until its wore out. DAMHIK...

[PA1195]

Re: Lost engine oil pump prime

Could be any or all of the above helpful comments...plus another. The engine has excellent oil pressure at initial cold and after run hot idle (max 40/min 20) and was overhauled by Custom Aircraft Engines in Palmer, AK., a thorough shop. It's possible the pump tolerances are on the loose margin as noted but there may be other engine components at play.

One thing I noted but didn't mention was that the screw-on Champion oil filter was essentially empty when removed to prime the pump (see Post #4/maybe a tablespoon of oil came out). Here's a quote from my link in Post #1 above: "There is some significant anecdotal evidence to suggest that the problem is more prevalent or exacerbated by installation of the F&M oil filter adapter. I have never heard a reasonable explanation for this, but there are too many complaints to ignore." I've removed hundreds of oil filters over the years (cars/motorcycles) and those installed horizontally contain substantial residual oil when removed.

I'm not sure of the mechanism involved but it may involve the anti-drainback seal in the filter element, the design and manufacturing tolerances of the F&M filter adapter, or tolerances in the pump cavity and gears as mentioned by Tim. If there's an adequate seal on the drainback valve it should hold oil and not empty back through the pump over time. There are tolerances in the F&M's filter's center screw that fastens the filter element to the adapter. How those differ when the engine's at rest from the effects of a plain cover plate that's removed to install the adapter I don't know. Then there's the relative position of the pump gear teeth at rest that may affect any seal and drainage.

Edit: For reference here's a description of Champion's 48108-1 filter element (http://www.championaerospace.com/wp-..._Filters-1.pdf), and the F&M TAF-L oil filter adapter that's installed (http://www.fm-enterprises.com/product.html). For me it's there not to just filter the oil but also add some cooling effect via this: http://www.airwolf.com/aw/products/oil-filter-chiller

I'll monitor this going forward and report back if it continues to be an issue.

Gary

Re: Lost engine oil pump prime

I think Tim has good theory.

This has little or nothing to do with the problem at hand.

Last year when I did my C90 I lapped the pump cover into place which is kinda standard procedure.

Additionally I lapped the oil pressure relief valve plunger into it's seat as well, also standard procedure.

The noticeable thing was the amount of lapping that the plunger seat required. The seat was not well shaped at all.

Re-machining the seat would have been ok as well, I just did not have the tools so I lapped it.

The case had been sent to a shop and overhauled and tagged.

My point is that the overhauled cases need to be checked carefully at installation.

This could have something to do with the problem at hand.

A friend here did a C85 a couple of years ago and got new gears and I think had the cavity done too and had similar problems Gary. When I asked him if he checked the tolerance he had not. He figured just having new gears was sufficient and did not check tolerances. Perhaps the tooth to cavity gap was too big or the side clearance where the plate is. Or?

Point is that since he had not checked tolerance we may never know the cause.

Dave R

[astjp2]

Re: Lost engine oil pump prime

Oil pump cavity is probably looooooossssseee on tolerance, that is why you are losing prime. My airplane sat for 5 years and I had oil pressure in 15 seconds on the first start...after 5 winters in Delta..

[PA1195]

Re: Lost engine oil pump prime

Thanks Gary, Hopefully soon I will be using this method.
eddie

Hey Eddie...shot you a mail but hadn't heard back. How and when is the next flight?

Gary

[PA1195]

Re: Lost engine oil pump prime

I was in a hurry yesterday to get to the root of the problem so didn't do a search here for previous solutions. Here's a good prior discussion: http://vb.taylorcraft.org/showthread...e-relief-valve

From this, Harry Fenton's discussions (http://www.bowersflybaby.com/tech/fenton.htm), and reviewing the engine overhaul manual's diagrams I gather the -8 and -12 have different oil plumbing. In my case with the F&M oil filter adapter it was a quick solution. Even without the filter adapter just removing the left rear engine cover plate for the uninstalled but optional oil cooler would make it easy. I don't know if the tail up method works on -12 engines (?).

Edit: Hint...put a large plastic zip-lock bag over (mainly under) the oil filter before removing. Catches what little oil from the filter wants to soil the engine compartment. Takes a 1" socket on the Champion filter and retorque to 16-18'# on reinstall. Safety wire the filter of course to the adapter housing.

I already had a small oil syringe with plastic tubing attached for filling this and that so just sucked some oil out of a quart container and shot it into the side hole that's downstream from the pump.

My mechanic knew this procedure and helped the fix by teaching me to do it.

Gary

[Robert Lees]

Re: Lost engine oil pump prime

I pre-empted that potential issue after completing my rebuild (the engine had been inhibited for 5 years) by the same method.

Rightly or otherwise, I had been advised to raise the tail to allow the oil to flow down to the pump.

[ERicter]

Re: Lost engine oil pump prime

Thanks Gary, Hopefully soon I will be using this method.
eddie

[PA1195]

Went to start C-85/90-12 today after a few weeks off and no oil pressure after 30 seconds. Warm out now in Alaska +50F and XC 20W-50 oil pumps good. In deep cold I'd not be concerned, but now...

Shut down and called my mechanic. He said remove my oil filter and do this: http://www.skyportservices.net/Priming%20the%20pump.htm

Put about 1.5 oz in the oil filter feed hole until it ran out then reassembled. Had oil pressure at 40psi within 10 seconds. Works to seal the pump so it'll lift from the sump.

Engine has less than 100 hrs SMOH and overhauled pump cavity and new gear assembly.

Gary