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MG Midget and Sprite Technical - Rear main bearing oil seal
|I know I've been here before, but I'm about to replace the clutch again because of oil contamination. I have the Morris Minor Spares seal kit, which frankly has never worked 100%. I have always wondered about the design. The seal carrier sits on the original main bearing cap, which has to be machined flat, exactly flush with a new aluminium piece which replaces the original cast steel upper half of the scroll housing. The carrier is however only bolted to this upper half. So there is no clamping force onto the main bearing housing. I think this is a weakness, and I am trying to devise a solution. What do others think?
|L B Rose|
take a look at Steve Keil's solution described in the May 2018 copy of Mascot. He has devised a means of using a face type seal on the flywheel flange and only requires minimal smoothing and polishing to create a surface for the seal to run on.
|Hmmm...the Peter May one is only for 1275 and looks identical to the Morris Minor one, even down to the tools supplied. The MED one looks interesting, as it appears to be bolted down on both halves. Sadly I'm not a MASC member, so don't get Mascot. Anyone got a copy?|
|L B Rose|
|Les, it's very easy to join MASC. And they aren't choosey - l think even you would have a reasonable chance of being accepted. You know you should! You would then get access to back copies of Mascot magazine as well. |
The conversion l mentioned is reckoned to cost about £5 and has been successfully road tested for over a year.
|The design is flawed in one important respect - there is no way for the oil that gets between the housing and the seal to return to the sump, so it builds up and eventually forces its way past the seal.
I use the front cap bolted to the rear cap and mount the pair in a lathe to grind the mating face of the rear cap perfectly flat - see pic.
Then drill a oil drain through the mounting plate and the rear cap at the lowest point.
Assembled with hylomar on the mating face and the lack of lower mounting screws doesn't matter.
|Chris at Octarine Services|
|Chris's method looks interesting, mainly because I am already fed up with the second/replacement seal I bought from Peter M letting the garage get rustproofed soon after fitting it|
I suspect even he has little faith in that method
|The best place for the MMC or PM one (same thing) is the bin!|
I tried one and went straight back to the good old scroll seal - I'd rather have a weap than flood!
I've heard from a few places that the Keith Calver one works but I think machining is required so it's an engine stripped job.
|"I've heard from a few places that the Keith Calver one works but I think machining is required so it's an engine stripped job."|
Yes Peter Burgess recommends it - and yes it's an engine strip plus machine work or I'd have had one recently whilst the engine was out (again).
|The Calver one looks the same as the MED one (and is for 1275 again), although I like the split seal idea as it is much smaller. I wonder about the longevity of that huge seal running on the edge of the flange, at up to 7000 rpm. The flange has a Speedi-Sleeve on it so is exactly the right size and perfectly smooth, but even so....
I already had the cap machined flat so I think I'll try the drain hole idea. I'd prefer to avoid an engine strip at present, as there is nothing else that needs it.
I spotted from the start that there was no way to drain oil out of the cap, and of course replacing the top housing destroys the scroll effect.
Not sure if Hylomar will be the best sealant for my installation. I can only get the backplate on by easing it over the oil pump and sliding it down slightly. It won't go straight on, so I have to use a sealant that allows repositioning.
|L B Rose|
|Les, I have looked at this for our 1380, and spoke to Peter May a number of times about it. Each time he said to keep away from the 'rear seal' conversion on a modified engine, so I get drips!|
|As I understand , it is common for the crank surface that this type of seal runs on, to be up to 10 thou eccentric which puts a lot of stress on a radial contact type of seal. I wonder if this radial eccentricity is intentional to provide a pumping action to the scroll seal operation?|
The version described in Mascot uses a seal that aligns axially with the crank, giving a more constant contact surface.
This thread was discussed between 04/09/2018 and 05/09/2018
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.