Looking back in this thread and thinking about it, I got to wondering what the purpose of the collars and springs could be, and I think it must have been to prevent pushrod bounce. Perhaps to reduce noise. It might be related to specified valve to rocker clearance. Clearance spec on my '38 SS is .012" where on my '50 Mark V it is .012" intake and .015" exhaust. I don’t have the factory spec on Mark IV.
So they actually increased the clearance on the exhaust valves.
I wonder if they eliminated the collars and springs, either because it was a potential failure mode, as Darryl saw; or perhaps they found another way to reduce noise, or just a cost cutting move?
Thoughts, anyone?
The 1.5 MK IV clearances per the owner’s handbook and the brass data plate are both .012 but there’s a service bulletin (copied in a file I can’t find since moving house) which increases the clearances. Used to be annotated by a previous owner on my scuttle beside the battery, but recently resprayed over. IIRC it was increasing the exhaust to .015.
Service Bulletin No. 14 dated February 1947
1946/47 1-1/2 Litre Engines
It should be noted that certain modifications have been made to the combustion chamber of the cylinder head on the 1-1/2 litre engine, and that from Engine No. KB.3099E no compression plate is fitted.
It has also been found advantageous to use an increased valve clearance, the recommended clearances now being: -
Inlet - .015"
Exhaust - .018"
However, in Feb '48 with Service Bulletin No. 23:
Compression plates came back from KB.4983 RHD and KB.6810 LHD.
Valve clearances on 2-1/2 & 3-1/2 Litre engines
To obtain improved slow running, the following clearances are now recommended:
Inlet - .012"
Exhaust - .015"
And since I’m sitting here on a cold evening reading Service Bulletins:
SB 32 date 30 Dec 1948
Push Rod Return Springs
Return springs are fitted up to the following engines:
2-1/2 Litre P.1508 RHD PL.1508 LHD
3-1/2 Litre S.3485 RHD SL.3503 LHD
Engines bearing numbers subsequent to above, also Mark V engines H.2001 onward and T.5001 onward, are not fitted with push rod return springs, and a new type of outer valve spring C.2135 is used. On these engines push rods are detachable when the rocker gear assembly is removed.
