Bob.........you mention wear marks on the cap above the driven gear. Let's
just double check - by this, you mean the one that rides on the idler shaft,
not the one that's on the shaft driven by the cam? If I'm on the same page
as you, then the problem may still have been caused by the gears being too
tight once they got really hot.
If the gear isn't perfectly at 90 degrees to the inside of the pump body, or
to the driving gear, it can rub or bind. I always make sure that the radial
clearance between this driven gear and the case is the same all the way
around, and also that it is not meshing tighter at the top of the driving
gear than at the bottom.
Even though the shaft that the driven gear rides on looks pretty solid, it
is possible to move it about with a big, soft hammer. (I use one of those
Compothane, sand-filled ones.) A few hefty taps in the appropriate direction
will move the shaft sufficiently to enable the gear to have uniform
clearance in all directions.
As to cam choice, I can only say that I used a Crane T-3 in one engine and
found it really would work only at high rpm; below 3,500 it had so much
overlap that one could see the fuel spitting back out of the carburetors.
Most of my T-racing was done using a regrind that was similar to the factory
competition cam.
Lawrie
-----Original Message-----
From: Bob and Carolyn Grunau <cgrunau@pathcom.com>
To: Lawrie Alexander <Lawrie@britcars.com>
Cc: MG T List <mg-t@autox.team.net>; T-ABCs_Forever
<T-ABCs_FOREVER@publi-consult.com>
Date: Friday, February 26, 1999 4:18 AM
Subject: Re: TC race cam troubles
>Hi Lawrie, I checked the gear end clearances with feeler gauges while
>building the oil pump. Yes, the new gears were too long and I had to
>machine some off. I aimed for 0.002" clearance. The book says 0.0016" to
>0.0035" so I thought 0.002" was safe. When I installed the pump I checked
>the installed clearance with plasti-gauge and it was 0.002".
>After the failure I re-installed the oil pump and the clearance is still a
>full 0.002" using plasti-gauge.
>It is possible that after a high speed run between 4,500 rpm and 6,000 rpm
>on the road the gears expanded and made slight contact with the cover.
>However only the driven gear shows any marks on the cover and this only
>less than half way round and some of this mark was present when assembled.
>I don't think it was a clearance problem but more an oiling to the gear
>problem.
>The information is still coming.
>So far, nobody has suggested a new race cam, any suggestions???
>Bob
>----------
>><mg-t@autox.team.net>
>> Did you fit new oil pump gears when you were building the engine? Did you
>> take the time to measure the end clearance between the new gears and the
>oil
>> pump cap?
>>
>> The problem you describe has happened on several engines with which I'm
>> familiar (though, thankfully, not ones I built!) The gears are just a
>skosh
>> too long and, when they heat up, they bind in the housing. The weak link
>is
>> the gear on the shaft, so this shears off. In one instance, it then
>jammed
>> between one lobe of the camshaft and the inner wall of the block. Room
>was
>> made for it by a large piece of the block exploding
>outwards..............
>>
>> When fitting new gears in an XPAG or XPEG oil pump, it is imperative to
>make
>> sure there is 3 thou clearance between the ends of the gears and the
>cover.
>>
>> Just a possiblity..........
>>
>> Lawrie
>> British Sportscar Center
>>
>
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