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MG TD TF 1500 - Oul pump failure again!

Doug Pelton From the frame up has a proper upgrade for this as has Bob Boast in Australia
From ttypes: Full article https://ttypes.org/xpag-oil-pump-rebuild/
Failures of replacement circlip in XPAG oil pump

Recently, several XPAG engines have been seriously damaged due to the breaking up of replacement circlips provided in some oil pump rebuild kits.

Due to the position of the oil pump, the rotation of the camshaft’s skew gear tries to draw the mating skew gear and drive shaft of the oil pump into the crank case. This axial force is resisted by the circlip retainer at the pump end of the drive shaft and prevents the drive shaft being pulled through the pump’s driving gear.

Failure of the circlip would allow the flange on the drive shaft’s skew gear to slide into engagement with the camshaft’s skew gear, with resultant damage to the skew gear and cutting off the oil supply.

The original fastener was a ‘snap ring’ (No. 1 in photo), which sits in a groove 1mm deep, machined into the end of the drive shaft. Such ‘snap rings’ seem to be unavailable, so a circlip is used instead (No.2 in photo). These are made from spring steel and to prevent overstretching when fitted, are only designed to have a 0.5mm deep engagement in the shaft’s groove. A further restriction on the circlip is the need to fit its protruding ears within the counter-bored recess in the pump’s end cap.

The combination of a shallow grooved drive shaft and a light duty circlip has resulted in failure of the circlip, particularly when engines are run at high oil pressures and high revs. These issues are unfortunately compounded by the replacement driving gear being chamfered at the face that meets the circlip, possibly causing the circlip to distort and eventually break up, as shown in the drawing.

This image has an empty alt attribute; its file name is xpag9-722x1024.jpg

Bob Lyell has obtained an inverted circlip (No.3 in photo) from Doug Pelton and although this is an improvement, the 0.5mm depth groove in the new drive shaft still does not match the original 1mm deep groove for security.

Is it possible to find a circlip intended for a 1mm deep groove? Unlikely, as expanding the circlip over the drive shaft could overstretch the circlip beyond its elastic limit.

How did the original ‘snap rings’ work? They were not made from spring steel, but from a ductile tough alloy that could be squeezed into the groove and retain their shape.

I have made some ‘snap rings’ (No.4 in the photo) from EN16 grade steel, which is a high tensile, fatigue resisting alloy and am conducting some tests on their properties. However, to use such an original style ‘snap ring’ means that the groove in the replacement drive shaft would have to be machined to a 1mm depth.
Eric Worpe
I do not like selling camshafts for this issue & when this happens it does damage the camshaft!
Len Fanelli

Len,

The correct type clips are available, they are called "constant section external snap rings". here is a link showing some.


https://daemar.com/ring-masters_58.html/

John
J Scragg

The damage caused by the use of these incorrect circlips is an expensive fact with the potential to destroy an engine. I have a few used camshafts, one of which has a chipped tooth on the oil pump drive gear (the cause of the damage is unknown) and I have been advised that it is not economically repairable. Earlier posts on this topic mentioned damaged conrods. I'd be very interested in hearing from anyone who has fallen foul of these Moss circlips. Please contact me offline at pjbm at bigpond dot com. Any pics that you have would greatly assist me in compiling an article for the benefit of TTORC members and others who may like a copy. You can remain anonymous. The cost to rectify the engine damage could easily run into thousands. The big question of course is 'Will the supplier accept responsibility for the damage caused?' No prizes for guessing the answer to that one... Caveat emptor.

I don't understand this comment however at the bottom of the post above? 'I do not like selling camshafts for this issue etc.?' Can you elaborate? Cheers
Peter TD 5801
P Hehir

Talk to some of the rebuilders, like Butch Taras. I've never heard of his rebuilds failing. I have one in my car with lots of miles on it.
Steve Simmons

It's not so much the circlip that fails it's the piddly groove depth(0.5mm) in the replacement shafts and the combination of the thin circlip and the chamfer/keyway on the top of the gear flicking the circlip out of it's groove- If the groove is machined out to original size (1mm)and the larger original size circlip used it can't fail as the drilling in the outer housing prevents any possibility of it getting out
The original circlip wasn't spring steel ,it was softer and squeezed into the groove with the tight clearance in the endcap preventing it from expanding

Here's a good read for you-
https://ttypes.org/xpag-oil-pump-rebuild/
William Revit

Read the update on the "engine noise" thread on the MG exp. board. Yikes. The ultimate responsibility is with the engine builder. Years ago a well known T-series guy told me that sometimes a part was reproduced from original drawings, however a running change happened before or during production. So the reproduced part is not correct, etc. Does anyone know when these parts came out? George
George Butz III

Steve-George
You've hit the nail fair and square on the head-
There's a difference between a pro engine builder and a bloke that puts an engine together-----

willy
William Revit

When my XPEG was rebuilt, it was done by an ex MG dealer mechanic. Extremely well done. PJ
PJ Jennings

Look closely at the pictures of the current Moss kit- it uses the same type circlip that is sold by FTFU. The shaft groove appears to be deeper than 1/2mm as well, but no way to tell for sure. This makes me wonder what type of clip I had when rebuild done 12 years ago. I was the engine builder in this case... George
George Butz III

This thread was discussed between 20/06/2020 and 24/06/2020

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