As my ‘Extra hole in the block’ post outlined, I am doing some maintenance on my 1948 Mk IV and originally planned to refurbish a spare head and swap it for the original, along with a radiator clean out and a refurbished water pump.
That WAS plan ‘A’!
The car is dated August 1948 by the JDHT and has the original engine S 3354 in chassis 612900
I purchased the car as the third owner in January 2003 when it had done 45000 miles, and mechanically it is in pretty much original condition, but it had been to Repco for some engine work (judging by the paint job) at some time, but no details or receipts unfortunately.
A tune-up on a dynamometer a few months back revealed a burnt valve, so with the enforced Covid-19 restraints I took the opportunity to replace the water pump, clean the radiator and swap the head for a refurbished one.
Today saw the head ready for removal, with rocker-cover off and rocker shaft off, but I could not release any of the push-rods… except one. The rest were held tight and by what felt like a spring. I had closely examined the illustrations in the workshop manual for the Mk IV and noticed a small spring surrounding the base of the pushrods but had been advised previously that these had been discontinued on the later versions in the Mk IV production.
However, there was no way the remaining eleven rods would lift out, so we lifted the head clear over them.
With the head off, still no clues, and my friend reported that on all the engines he had seen the push rods simply lifted out of the block. Definitely not in my case, so I removed the tappet cover plate. Those of you who have done this job with the engine in situ will know that it is almost impossible to see in there unless you have the dexterity of a ballet dancer or gymnast. So out came a bright light and a mirror, and to our surprise, there were springs on each of the pushrods.
A quick read of the Workshop manual reveals that indeed I do have to fabricate the appropriate tool to lift the pushrods against their springs so that the ‘Tappet Blocks’ can be withdrawn, and although it does not mention this, presumably then I can release the pushrods, the spring tension comes off and the collars can be removed and the pushrods pulled up through the head. It also mentions ‘cups’, but I have yet to find any reference to them in the illustrations. Apparently, I will also have to withdraw the rev-counter drive shaft to release the centre tappet block.
With my aging facet joints, my back is not going to stand for any time attempting to do this with the engine in position so getting the pushrods out will mean an engine-out job. While I am a little disappointed at the outcome, it will mean that I will be able to deal with the other issues that I was putting off, namely a badly leaking gearbox, a check of the clutch and an inspection of the bearings!
I also want to look closely as to why one pushrod is free – I presume the collar has failed. The car ran fine up to the dismantle.
I have attached some pics of the bowels of the valve gear for those of you who have not come across these springs.
I would be interested in any readers experience or knowledge of the pushrod springs, whether they were supposedly only on earlier models, and anyone with experience of their removal. I am aware of the note by Barrie Price in ‘Rise of Jaguar’, but I can assure readers that the engine number is correct and assume the Heritage trust got the build details and date correct, so it seems I have a later engine but with what was later seen as superfluous push-rod springs. I cant imagine any mechanic reinstalling them but … who knows?