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Re: HELP !! [fuel mixing in oil on TR6 (fwd)

To: triumphs@autox.team.net
Subject: Re: HELP !! [fuel mixing in oil on TR6 (fwd)
From: "Michael D. Porter" <mporter@zianet.com>
Date: Tue, 03 Aug 1999 14:25:46 -0600
Cc: Mark Simon <msimon@ocdus.jnj.com>
Organization: Barely enough
References: <Pine.WNT.3.95.990803104228.-355761J-100000@win2431.nysed.gov>
Andrew Mace wrote:
> 
> Hi. Would anyone care to offer Mark some help? Please reply to him, not to
> me!
> 
> --Andy

> Subject: HELP !!
> 
> Dear VTR,
> 
> I need some advise if I can get it.
> 
> I have a '74 TR6 in excellent condition - restored about 3 years ago.
> 
> For the past year I have had some serious issues with getting fuel into
> the oil. It is most noticeable after the car sits with a full tank over
> the winter, however it is also noticeable with normal use. After the
> winter the crankase is nearly full and the engine cannot be started for
> fear of blowing a gasket or something.
> 
> This past season I paid a (supposedly) qualified mechanic to rebuld both
> carbuerators with new seats and gross jets to replace the standard
> needles. He indicated the issue was that the needles were 'sticking'
> open and allowing fuel to pass by. Unfortunately this has not cured the
> issue.
> 
> Can you provide any additionasl ideas here ? I have already replaced the
> fuel pump last year as I was told that that could be the issue too.

As for normal running (discounting the full crankcase in winter for a
moment), the things which typically do not come with rebuild kits today
are floats. These could be starting to go bad, so that fuel level is too
high in the bowl. If this were the case, differential cooling after the
car is shut down can cause fuel to thermosiphon out of the main jets and
into the manifolds, then into the cylinders. If hard starting from wet
plugs occurs after the car sits overnight, or if you never have to use
the choke, because the cylinders are already wet, this could be the
problem. This phenomenon can continue until the float bowls are nearly
dry. Some of that fuel, of course, will eventually leak past the rings
into the crankcase.

Concerning the full crankcase over the winter, this must have something
to do with the fuel pump, as well. The pump is principally composed of
an actuating lever pushing against a diaphragm, an inlet valve and an
outlet valve. In normal operation, when the lever pushes on the
diaphragm fuel pressure forces the outlet valve open, and fuel moves
into the delivery line and the pressure drops, and the outlet valve
closes. The lever retracts as its arm moves off the pump cam on the
camshaft, the diaphragm relaxes, which causes a partial vacuum in the
pump chamber. This partial vacuum opens the inlet valve, fuel flows into
the chamber, filling it in preparation for the next discharge cycle.

For enough fuel to fill the crankcase when stationary, both the inlet
and outlet valves must be open, even to a very small degree, otherwise,
fuel cannot flow through the pump. 

I think you need to look carefully at the pump and the floats. It's
possible that the problem lies in one or both of those areas, although
there is one more consideration. If you regularly buy fuel with lots of
water or dirt in it, _everything_ will eventually stick open, either
from corrosion or from debris. If you do decide to replace the pump and
or floats and float valves, try putting a high-quality fuel filter
before and after the pump, and ensure that the tank and feed lines are
clean. This will ensure that debris from the tank does not enter the
pump, and that small scarf from pump wear does not enter the
carburetors. 

To determine if the problem is water in the fuel, gas it up as usual,
then drain about a quart of fuel into a jar, then let it stand
overnight. If the water content is high, the water and gasoline will
separate into clearly different phases. Be aware, if you are in the
habit of buying high-octane fuel, most unleaded gas has its octane
raised by the introduction of ethyl alcohol. High amounts of alcohol and
water together will accelerate the rate of corrosion in the fuel system. 

Cheers.

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