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MG TD TF 1500 - Moss Seal Leak Test

After Installing a few Moss Seal Conversions I wanted to confirm what leaked after the installation. The seal is the first to get blamed, after the pan has been installed and the engine run. I decided to investigate this. I left the pan and flywheel off, sealed the crankshaft flywheel mount holes and dowel pin holes and flooded the cavity as in the photos. So far I've found the main source of a leak is the area where the rear main cap mated to the old slinger, once this was corrected I could be satisfied the Moss Seal wasn't the leak!
Kim H





W K herford

Impressive.
Christopher Couper

They do get blamed a lot, because the leaks are so hard to find sometimes. Another option is to put some oil in and tip the engine up on its rear. Return a while later and see where it leaked.
Steve Simmons

Can you provide more detail as to where the leak occurred, and how you fixed it?

Many thanks. Tom Lange
MGT Repair
t lange

Why do owners persevere with this solution when there are better options?

I installed a Moss seal on my XPAG the only way I could prove the assembly was leak proof was to run the engine removed from the vehicle.

Despite doing this within 500Ks I had a leaking rear end.

Far better is use a conventional method of installing a main rear seal that is utilised by all modern engine builders.
G Evans

G Evans. I’m curious to know what conventional seal approach you are speaking of since there was no seal originally. The only two options I’m aware of are the Moss type conversion or that using a Small Block Chevrolet rear seal. The later not being a reversible procedure.

Bill Chasser
TD-4834
W A Chasser

First I dont believe fitment of the Moss seal option is totally reversible without replacement of items that have to be modified to facilitate fitment.

Yes both the Chevy and the Volvo rear seal fitment requires irreversible machining to be carried out. If you want a solution this process is well worth it.

Line boring and refurbishment of the scroll are advocated by many as a solution, might be if you are owning a show pony T Series, however if your doing multiple Ks it will not be a permanent fix.
G Evans

There are a couple potential modifications to fit the Moss seal, depending on the particular engine, but nothing that has to be reversed in order to go back to the scroll. More of a clearance issue is all, and only on some engines.
Steve Simmons

Hello Again,
When testing the Moss Seal I would remove the Pan, install a tube on the drain tube installed on the lower rear main cap, flywheel removed and mount bolt holes and alignment dowel holes plugged. Then flood this cavity.
The first one I had done the main cap leaked badly and I found a gap between the block and cap where the seal carrier mated. .050 x 3/8" long and both sides. This block had been extensively worked on and line bored. The new crank positioned the moss carrier lower than the block flange. I cleaned and used JB weld to bring the 2 mating surfaces together making sure the rear main tolerance was kept. This worked as no leaks after.
I have found some of the seal carriers to be within the sealing range of sealant and managed to stop the leak.
The pan gasket is many times the bad area where the cork, paper and pan all meet. This needs to be done as per the manual! Sealant in the corner cavity then gaskets and cork.
Cheers,
Kim Herford
W K herford

This thread was discussed between 31/07/2021 and 10/08/2021

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