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Scroll Seal Suggestion


The rear crankshaft scroll can be fully leak-proofed by a high temp. VITON 63mmx4mm 0 ring stretched over the crank flywheel flange and tensioned on the crank web between the surface ground and polished face of scroll and inner flange face - this gap is approx. 4.4mm ( if significantly different may need a thicker or thinner 0 ring ).   This 0 ring is permanently tensioned against the scroll by a further H.T. VITON 63mm x2.62mm 0 ring stretched over the flange and which automatically sandwich/tensions itself between the outer upper edge of the 4mm 0 ring and flange. See attached sketch:-

Both 0 rings are sufficiently tight on crank to spin fully with crank. The 4mm 0 ring receives lubrication from the very small amount of oil constantly trapped at rear of scroll.  N.B. To achieve 100% success the new scroll must be perfectly  aligned. The clearance between the inner circumference for the scroll and the outer circumference of crank scroll is only 0.002 of an inch and an expert repco engineer of the "old school"once advised me that if any part of the scrolls touch then the seal becomes ineffective. Therefore precise alignment is paramount. Alignment if not by way of "crankshaft out" and "Factory  Mandrel" ( now available ex. Moss USA )   can be achieved with "gear box out" F wheel, sump off and bot. bearing cap extracted and following a precise sequence aided in the main by a strip of 0.002 steel shim.

Having obtained a new scroll from Register proceed as follows:-  Firstly surface grind the two unmachined casting faces of the outer scroll halves to a flat and smooth surface. I achieved this by firmly holding the two halves together and with light pressure moving them back and forth over fine wet emery paper  laid over a piece of 3/4" plate glass.  Then polish with metal polish out from the scroll edge to a mirrow finish. Obtain a small sheet of 0.002 of an inch steel shim. With the rear main bearing cap extracted, together with attached half of old scroll, remove 4 bolts from upper scroll half. Rotate anticlockwise the old topscroll half around crank 180 degrees and remove through bearing cap aperture.  Cut a strip of shim steel about 25mm wide and 250mm long. Lightly machine oil both sides of shim and inner scroll surface. Lightly coat inner flang face of new scroll with Locktite automative number 3 non-hardening aviation gasket sealant.  Lay shim inside scroll half with approx. equal lenghts hanging out both ends. Carefully rotate the scroll half with the shim  inside around the crank in the reverse direction to which it came out. The process is to get the top half back in place with the shim entrapped between the two scrolls with a small length of shim protuding at the far end.

I suggest you have a few "dummy runs" (without gasket sealant) until you get the knack of it. Once you get the scroll home and are happy the shim is fully covering the scroll ( not too much hanging out the front face ) insert  and finger tighten (then back off 1/2 turn)  the 4 bolts.  Apply a light to medium downward pressure on scroll, sufficient to sandwich the shim between scrolls, but not so much as to preload  the shim to a level that you can't pull it out.  Holding  tension, fully tighten the 4 bolts.  Using pliers pull directy downwards on the long exposed end of shim. If it starts to pull out relatively easily with medium tension and no fear of tearing  continue in one motion and pull out completly. If not loosen bolts , apply less downward force and retighten bolts and try again. Don't worry if you need several attempts as you soon get the feel of it.  Attach  new bottom scroll to bearing (using gasket sealant ) cap leaving bolts loose. Tap home the bearing cap making sure bearing shell is ok and still properly in place. Bolt home the bearing cap and tension  bolts per workshop manual (use gasket sealant to top and sides of cap before fitting.)  When the bottom scroll is fully mated to the top half there will be 0.002 " clearance at the bottom of the scroll only.

Lateral adjustment is achieved by fully inserting between scrolls a short piece of shim about 25mm wide adjacent to and immediately below the left join.  Insert the small shim as above and using forefinger of left hand apply lateral pressure to sandwich shim and simultaneously use left thumb to apply upward pressure to close the halves together.  Maintaining pressure tighten bolts with right hand.  Repeat as previously if shim is too tight to remove.
Some rcommend gasket sealant to the 2 segment joins.  I would put a very light smear on the join of bottom half but clear of the internal scroll channel edge.  If excesss gasket sealant is used it could well flow through and run into the small scroll channels blocking same with adverse results. You now need to seal the rear bearing cap - see service instruction manual page 33.

 If you need a "quick fix " (but unprofessional ) make a small narrow tray out of thin Zincalum fitted directly under the bellhousing to gearbox join fixed by 2 of the bolts to this joint. Fill tray with felt wadding.
Colin Cuffe ......2014

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