Race Engine Forum UK

Hello,
I have a question, is there any particular reason for oil seal to jump out of the housing in the front of the crankshaft on engines with oil pump driven from crankshaft? The problem happened few times on 1,2 16v Fiat engine from Punto(in few different engines) and the only way to solve the problem was to replace the oil pump but this does not answer the question: why it happens?
In my opinion it happens if the pump is a bit worn and pumps the oil in the space between the oil seal and the oil pump gears, after it fills the gap with more oil than can escape by the drain hole to the oil sump then it builds some pressure that presses out the oil seal. Am I right or there is some other explanation for this?
The engine is revved to 8000rpm.

I have not personally exp this but I guess excessive crankcase pressure or crank end float can do it. If the front pulley array is rubbing on the seal it will overheat and loosen it.

As for oil pressure the relief valve should take care of any excess build up - dismantle and make sure it's correctly assembled - on some pumps you can put the piston in the wrong way round and it doesn't vent off. Sticky piston is something I have seen too. Normally you'd see very high gauge pressure in that event though.

Sorry, no definitive cause, some fault finding needed maybe?

G

I will investigate it for sure but crankshaft float will not be a problem as well as worn sealing surface that would damage the oil seal lip as after only replacing the whole oil pump without touching anything else in the engine the problem goes away.

As for the oil pressure that presses out the oil seal I do not mean oil gallery pressure but the bleed on the oil pump(then it will not give a good oil pressure to the gallery).I mean the oil that bleeds from the oil pump between gears and housing to the space where the oil seal is located, but that is just a guess.
I will try to find out what the problem is.

Tomaz

usual practice is to have a drain slot to the sump just behind the seal, eliminating risk of the pressure ever pushing out the seal. That is - when the relief valve is functioning properly.

GC

I've a feeling I'm pointing out the obvious here but some oil seals have a rubber-like coating on the metal ring, mostly to prevent oil oozing between this ring and the part the seal is installed in (in this case, the engine front cover). However, this coating also makes the seals a bit harder to drive in, and in turn, it makes them stick harder to their landing places so they won't come off as easily...

A good example of seals with this rubber coating are those used on some differential pinions. In the event the diff vent becomes clogged, the built-up pressure can escape between the seal lips and the pinion itself (along with some oil drops of course) instead of blowing the seal out.

Sure.

You can give the polymer a very light smear of oil before pressing but in some cases I have adopted a practice of warming aluminium housings to around 60 deg C (hot water will do or pop them in an oven) before fitting polymer coated seals, generally they will just drop in at that temp. Particularly important with the TC crank rear seal housing, given that they are pretty old now they can crack if you press the big crank seal in.

GC

I have checked the oil pump today and there is no oil drain hole between oil seal and oil pump gears. Also the clearance in that pump between gear and housing was excessive(about 0,20mm) which for sure was not good and could lead to pressurebetween gears and oil seal. The oil pump is replaced to new OEM unit and hopefully the problem will not occur.

This leads to another question. Should the oil pump be replaced if the bearings on crankshaft let go? I ask because there is a high chance that the bits from the bearing will for sure be sucked by the pump and can it be prevented by using a fine mesh on the oil pickup?

I always at least disassemble the pump and check for wear and or damage from FOD.

The screen is coarse for a reason, so it only stops the large particles that would cause instant pump damage. The limited surface area can be blocked very quickly with debris then the entire engine would be damaged instead of the bearing generating the debris.

Robert

Right on, Robert.

FOD - for the non-English speaking (non RAF?) foreign object debris..

GC

Guy,
Sorry for the acronym. I meant to elaborate but posted and forgot. FOD is an item in a preflight inspection and walk around checklist where the aircraft may have damage from a foreign object striking a propeller or leading edge. Also the team that walks the drag strip after a car oils down the track looks for pieces that may cause FOD. Not good at 200+ MPH. EEEK

Being a licensed A&P (air frame and power plant tech) these acronyms slip by.
Again Sorry....Robert