Rear main bearing seal for Grey motor

[Fraze]

Can anyone suggest a source to buy the rear  main bearing seal (rope seal) for the Holden grey motor. I am not happy with the stuff supplied in the bottom end gasket kits. Prefer a source around Melbourne. Thanks,Frazer

[ardiesse]

Fraze,

A few suggestions -

I think the rear main seal material is called Graphtite.  chevsofthe40s.com lists the rope-type rear main seal under the part number 3835774G, and says it's a replacement for the original seal which contains asbestos.  I don't know if the Chev rear seal has the same width and depth as the Holden one though.

Your local bearing supply place should sell graphited rope-type seal in bulk, for marine-type applications.

Or (just for what it's worth, and perhaps not to be taken entirely seriously) - if your old rear main bearing seal wasn't leaking before, and if you removed it carefully from the block and rear main bearing cap, why not re-use it?  You could gently re-form its profile so it seals positively on the crankshaft.

But I thought that you'd cured the leak out of a newly rebuilt motor . . .

Rob

[Fraze]

Thanks for that info Rob.
I too thought I had cured the leak, it was good for a 1000 miles or so but after a 55-60 mph run on a hot day it started to leak again, not as bad as before but still I don, t like it. When I get a bit of time after Xmas I will pull the engine and have another go at it, but I won, t be using the "rope" as in the gasket kit.
Any other suggestions or alternative gratefully accepted!!!

[ardiesse]

Fraze,

Just make doubly sure that the leak is indeed coming from the rear main bearing, and not from any of -

the oil filler cap (via the rocker cover and the back of the motor)
the rocker cover gasket (via the back of the motor)
the pushrod cover gasket or any of the spark plug corks (via the lower rear corner of the pushrod cover)
the dipstick (not joking)
the distributor (the rectangular section O-ring goes hard)
the crankcase breather pipe (not joking either)
the sump gaskets
the oil drain plug

and finally

an over-filled gearbox (in this case the oil will smell like gear oil).

Degrease the motor and gearbox well, even to the point of wiping it all down with clean rags.  Take the clutch cover off, and wipe the back of the sump clean.  There's a semicircular relieved section in the rear main bearing cap just in front of the crankshaft hub.  If you can work a rag into there with a screwdriver and wipe it clean of gunk, that's good too.  Wad rags up between the cylinder head and the firewall, and at the lower bottom corner of the pushrod cover.  Now you can start the engine and inspect for leaks.  With the clutch cover off, the rear main seal will leak out the bearing cap and either drip off there or run down the back of the sump.  It won't usually fling oil off the flywheel.

When I spat my new rear main seal, most of the fibrous gunk ended up in the semicircular channel in the back of the rear main bearing cap.

And if the leak is from the rear main, how fast does it leak?

Rob

[Fraze]

Rob, I have done most of the things you suggest, but your post is all great advice.
I find your comment about the gearbox leaking very interesting because the small puddle on the garage floor after a run seems to be 2 colours. First there is a small amount - maybe a few drips - which are a very dark colour and correspond  in colour with the oil track down the back of the sump from the rear main, and which hang off the sump plug. These drips are apparent immediately after stopping the engine.
After standing overnight, there is more oil which is of a light colour which seems to be coming from the drain hole in the bell housing - these two oil patches form the same puddle but the two colours are quite distinguishable.
The light coloured oil looks like  clean engine oil. I am using a Penrite gearbox oil which is tinted blue in colour.
I do have a bit of weeping from the front seal but and I thought maybe the oil from there was blowing back and dripping off the gearbox causing this second puddle, but the front weep is not bad enough,and there are no oil tracks along the sump or along the side of the engine.
We are not talking about a lot of oil here,after a freeway run of about half an hour the dark oil patch is about the size of a 50 cent coin and the clean oil about 75mm dia. The clean oil patch sits on top of the dark oil. I have a smooth painted garage floor and I realise a drip of hot oil spreads, but it is annoying considering the time I have put in to try for a leak free engine.
The only other place where oil is apparent on the engine is a very small amount on the flange of the block below the fuel pump (EJ pump) but this is only a trace.
This is developing into quite a story!

[Fraze]

I just now removed the cover plate off the bell housing and around the cut out for the rear main there was pieces of shredded fibre which can only be the rear main seal breaking up- probably spun.
I will not be replacing it until I can find a better material than the rope stuff from the gasket kit;
ANYONE OUT THERE GOT ANY GOOD OLD (just joking)ASBESTOS PACKING OUT THERE!!!!
Cheers, Fraze

[weddo]

For what it's worth Fraze, I still use the replacement rear seal included in the bottom end kits in my race motor and have no problems between builds.
As long as it is installed corectly ie: soak in oil for 24 hrs, install with a setting tool, trim with a very sharp blade and leave about  1/2 mm proud both sides top and bottom before installing cap. (Slight gearbox oil leaks are another story)

regards
Weddo

[ardiesse]

Fraze,

I've been trawling around on the 'Net, mainly on Chev 6-cylinder forums.  More than one site notes the lower quality of today's rope-style rear main seals, which appear to be graphited fibreglass.  For example -

inliners.org/tech/261_build.htm and
Hemmings Muscle Machines March 2009 (Google "rear main seal").

The Hemmings article makes a lot of common-sense suggestions, like inspecting the crankshaft seal area for corrosion and burrs.

Graphtite is a trademark of the Best Gasket Co (http://www.bestgasket.com).  Their rear main bearing seals made of woven graphite (no asbestos, no fibreglass), and a lot of posts on the Net report success when using Graphtite rear main seals.

Which brings me back to six-cylinder Chev engines.  The pre-1955 and post-1955 Chev 6-cylinder engines had differently dimensioned rear main seal grooves.  The pre-'55 groove was narrower and deeper than the post-'55 groove.  And two-piece rubber seals were introduced post-'55.  (thinks: this is awfully reminiscent of grey motor/red motor rear main seals).

http://www.marxparts.com has a rear main seal page, with indexed links to the Best Gasket website for pictures of each rear main seal.

I'll go out on a limb here and suggest that you buy a part number 6100 rear main seal (1940-1962 Chevrolet/GMC 216-235-261) from marxparts.com.  It should fit a grey motor.

But I need to measure the dimensions of the seal groove.  Does anyone have a rear main bearing cap just lying around, to measure the dimensions of the seal groove?  Or does anybody know if the rear main seal groove in a pre-1955 Chev 6 is dimensioned the same as that in a Holden grey motor?

Rob

[Fraze]

I appreciate all of your help Rob. The rope seal in the kit is 3/8" square so I emailed Marxparts to ask if their seal 6100 is that size. If so I will order from them.
Alternatively, there is a company - Selectseal- which sells on ebay and they advertise a 3/8" graphite packing for $24 per meter which looks very similar. I have emailed them to confirm that their packing is suitable for hot engine oil.
We will see what sort of answers I get.
I had another look at the rope seal from the kit and I cannot fathom how it can be cut cleanly, I tried a hobby knife, a razor blade and finally surgical scissors and in all cases the end came out with lots of stray strands and all feathery.
I also looked at how to work it into the groove and I cannot see how that can be done properly, the rope seal I have  just does not have the density or plasticity required to be able to work it into the groove and stay there.
Cheers, Frazer

[Fraze]

Rob, the groove in the rear main seal area measures 6.5mm deep, 6.00mm bottom of groove and 8.5 wide top of groove. Looking at those dimensions, 3/8" (9.5mm) packing is too big. I contacted Marxparts in USA as you suggested and they are very helpful. The 6100 packing measure 6.35mm wide x 8.73mm deep so that would be too small, not enough crush. As an alternative Bob Marx suggested their 6380S packing which measures 8.6mm square. I think that will crush in nicely so I will buy that set. Cheers, Fraze

[ardiesse]

Fraze,

Interesting.  I was expecting that the rear main seal packing on a grey motor would have been 1/4" wide x 3/8" deep.  So the groove cross-sectional area is
6.5x(6.0 + 8.5)/2 mm^2 = 47.1 sq.mm.  The 6380S has a cross-section of 74 sq.mm.  When the 6380S is crowded into the grey motor groove there'll be 27 sq.mm left over, which is a rectangle 8.6 x 3.2 mm.  Take away the thickness of the bearing shell (assuming the crankshaft tunnel is machined out to the same diameter everywhere, and the sealing surface and journals are the same diameter), and you'll have maybe 1.5 to 2 mm crush.

Running the same calculation for the 6100, it has a cross-section of 55.5 sq.mm, which leaves 8 sq.mm of seal protruding from the groove.  Which is about 1 mm in height when it has squashed down to 8.5 wide.

So the $64 question is - what's the clearance between the crank and the top surface of the seal groove?  If it's of the order of 1 mm, then the 6100 would be a better choice.  Perhaps you could buy a 6100 as well, to be on the safe side.

Rob

[Fraze]

Interesting calculations Rob. I removed the rear main bearing cap from an engine which I think is original. The seal in it was spread right accross the full width of the seal area on thecrank, maybe 10-12.mm and the thickness between the cap and the crank is more like 2mm. I have some packing very close in dimension to the 6100 and it would not spread wide enough. I have several pieces of packing from gasket kits and they vary in size a little but are much closer to the 6380S actually a little larger.I have some 6380S on the way and will keep all advised.
Also I know a bloke who has some original GM asbestos rear main seal packing and he is going to dig it out and measure it for me.

[Fraze]

Rob, I forgot to add, I didnt actually measure the crank at the seal area, but it is much larger than the main bearing size, I'm guessing more like 54 .5 to 55mm,
Fraze

[Fraze]

Hi Rob. I got word back from my friend who has some of the original GMH asbestos rear main packing for grey engines. It measures in cross section 11.5mm x 7.2mm  (Dimensions vary slightly along its length but this is the average). That makes 82.8 sq mm. so I think I am on the right track with the 6380S packing. Unless my fairy godmother comes up with something better I will try the 6380S, fingers and toes crossed. I probably won't get onto it until 1st week January but will post when I have done the job. Cheers, Fraze

PS If it had been someone else's engine here I might have enjoyed this exchange of posts!

[fcwrangler]

Hey guys, been reading this with interest as I will be pulling my engine down and have purchased an ACL set from Robbo's. I have just been in the shed doing a bit more on the car, so I pulled the gasket kit out and measured the seals they have supplied.
The rear seals are graphite coated rope type and measure 120mm long 12mm high & 8mm thick approx.
Going by the GMH ones, these would appear to be close in size, so hopefully they will do the job.
Jim

[Fraze]

I'm beginning to think that the rope seal I am having trouble with might just be isolated to the particular gasket set i have been using. I have ordered a set from another source and we will see what sort of rope seal I get in that set. I probably shouldn't name the suppliers or gasket set manufacturers at this stage.Fraze

[Not Happy Jan]

How did this all end up??

[Fraze]

Well i gave up on the rope seal as supplied in the gasket sets, it is absolute rubbish, and used the 6380S stuff I got from America. It has been in for quite a few thousands of miles now and I am happy with it. I do get some leakage (not enough to concern me) but I put that down to the poor state of the crank seal area which is quite worn.
As a footnote, my Wifes nieces husband did his apprenticeship with Repco in their engine reco shop - I showed him the rope  seal out of the gasket set and he condemned it immediately as unusable.
Another footnote - I compared the 6380S seal with the seal supplied for the Holden V8 engines and it is very similar, just a bit larger cross section.

All good now, Fraze

[Rod]

Sorry to bring up an old thread. I have read multiple threads but can't seem to locate an answer. This thread seems the one closest to what I am after.

I have installed main seals possibly four times over the years and never given much thought to the direction that the seal is placed into the cap and block recesses. I have acccess to an original seal and plan on instaling it rather than the one in the gasket set. The orginal is very hard and not very pliable whereas the one in the gasket kit is very soft and very pliable. I can see how the latter fails in most instances.

The original seal I have is similar in dimensions to what Frase has mentioned in this thread (Mine measures about 11.9mm x 6.9mm). I know when I place the seal into the recesses, that it will compress but I was wondering which way I should put the seal in. If I was to place it the thin side in, ie: facing the bottom of the recess, it would not be a tight fit (possibly would be after compression). If I was to place it in thick side facing the bottom of the recess, I would need to compress it (make it narrower) along its length in order for it fit. Interestly the seal "feels" that it is easier to bend in a circular curve to match the crank this way rather than the other way.

I have got a lot of great hints from numerous threads and been making some backyard tools to assist the instal. All going well, I hope to provide some photos etc... this coming week once I am comfortable which direction the seal goes in. The last thing I want is a spun seal which in reading is possible.

Thanks in advance.

Cheers Rod

[my8thholden]

Rod ..I too have chosen to use the old seal material .it is wedge shaped if you look end on , the narrow edge in first , what ever seal you choose soak it in oil , and good drop on assembly as you do with your bearings ..I put the crank in 3 or 4 times , pain in arse , but less pain than a leaky seal ..when you first put seal in and work it in with a curved tool , then the crank flattens it a bit , if when you first put seal in measure it and say 10mm , after crank in and out it has flattened and say 12mm and wont push in any more that indicates crush on the seal and crank should turn by hand ,if it drags ,it a bit tight ,Vern