Roger Wilson has written a comprehensive article on the infamous engine leak at the rear of the block in the May 2010 edition of “Totally T-Type”. This excellent article prompted me to look at a spare ‘Gold Seal’ reconditioned engine block, which has revealed an additional problem and also paved the way for trying out an old remedy. In this article, the term “oil scroll housing” is used to describe that part of the “main bearing cap” that surrounds the oil scroll on the crankshaft.
The first step was to make up the setting gauge (Photo 0) detailed by Roger in the September 2010 edition of TTT.
This revealed that Roger may have been optimistic when he suggested that “The oil scroll housing on the rear main bearing cap will have a uniform clearance all round as it was bored in line with all the main bearing housings”. In this particular block I measured 0.006” clearance on one side, gradually diminishing to less than 0.001” on the other (Photo 1).
My first thought was that the setting gauge was not seating properly, so to eliminate the gauge, the rear main bearing cap was mounted on a mill table and a Dial Test Indicator mounted in the chuck was then used to check the concentricity between the oil scroll housing and the shell bearing housing (Photo 2) This confirmed the 0.006” misalignment.
A magnified inspection of the oil scroll housing’s surface suggested that some rubbing against the crankshaft’s oil scroll had taken place. This leads me to believe that wear in the main bearings could have been considerable, thus allowing the crank’s oil scroll to contact the housing.
But why double the wear on one side compared with the wear on the bottom of the shell bearing?
This might be explained by the tendency of a rotating shaft to climb up the bearing’s side. The location of the excess wear on the near side of the engine seems to support such an idea.
Rather than have the main bearing cap line bored, I chose to machine the oil scroll housing to be concentric with the bearing housing (Photo 3) and set up a uniform gap of between 0.01” and 0.015”.
The object of this slightly alarming approach was to make use of a suggestion by the late Ray Sales, some 15 years ago.
He ensured concentricity between the crank’s oil scroll and the housing by wrapping a single layer of sellotape around the crank’s oil scroll and spreading a thin layer of JB Weld on the oil scroll housing. The crank, bearings and bearing housings are then assembled, torqued down and the JB Weld allowed to harden.
On dismantling, the sellotape is removed along with any excess JB Weld. Such an approach should set up a truly concentric gap of about 0.002” (0.05mm). The extra clearance machined on the oil scroll’s housing allows a thicker, more robust layer of JB Weld and to improve adhesion a groove was also machined into the scroll’s housing (Photo 4) with a slitting saw.
The slinger cap or oil thrower is the die cast cover plate that sits directly above the crankshaft’s oil scroll and is meant to be located by two 4 mm dowel pins and secured by three M6 screws to the engine block. The dowel pins had been removed, perhaps confirming Roger’s comment about the Morris Engine Division (responsible for the Gold Seal reconditioned engines), having to remove the pins to help correct any misalignment.
Using the gauge, a gap of 0.004” at the top of the slinger cap and a tight fit at the sides was revealed, suggesting a new cap had been installed. A light skim of the cap’s flat edge on some 320 wet and dry (Photo 5) and some judicious scraping (Photo 6) set up a uniform 0.002” clearance with the gauge.
As Roger has advised, some semi-hardening sealant either side of the gasket would help fix the cap’s location in the absence of the pins once the cap has been secured by its three screws. The use of some 0.002” shim steel wrapped around the gauge would help true the fixing of the slinger cap to the block.
All the above procedures should secure a uniform 0.002” clearance around the crank’s oil scroll, and whilst some slight leakage may still occur, a well set up oil scroll system should be inherently effective.
My conclusions support Roger’s suggestion that the oil slinger’s dowel pins were not always able to set up the correct clearance and that some individual adjustment is needed with the aid of a setting gauge.
Although the scroll housing should be concentric with the bearing housing, excessive bearing wear can result in increased leakage as the crank’s scroll abrades away the scroll’s housing. This can be rectified by expensive line boring or by reducing the clearance with a film of JB Weld. For good adhesion of this film to the housing, some care in preparation is needed, such as the use of a ‘Dremmel’ to grind away and rough up the surface.
If main bearing wear can result in abrasion between the crank’s oil scroll and the housing, then the crank’s oil scroll diameter needs to be checked and the setting gauge dimension modified to be compatible.
When assembling the shell bearings, the ends should slightly protrude by a few thou. above the housing. This allows a slight degree of “bearing crush” to take place when the housing is torqued down.
I hope this article will give encouragement and the reassurance that paying attention to detail, although time consuming, is worthwhile.
Ed’s note: As always, Eric is willing to pass on the fruits of his labours and in doing so enables others to benefit from his experience.