Hydraulic Cam

[David Kemp]

Can someone enlighten me on the history of hydraulic cams with Jowett & why they stopped using them? A mates Dad said his new Javelin gave more power with a hydraulic cam, but had problems & was replaced by a solid cam. If this is so ,with new technology, would a return to hydraulic cam be now a benefit?

[Forumadmin]

I have not personally had experience of an hydraulic tappet engine but hope to soon. I am fairly sure the reason for dropping the system was that it was more expensive. There may have been technical reasons such as the system taking more oil than the feeble oil pump fitted to the early cars could deliver and this resulted in failure of the rear mains.

When I start on the engine we will inspect it as part of one of the Kings Langley garage days. Watch out for this in the What's on topics.

[PJGD]

I think that it was in the Profile Publication on the Javelin/Jupiter that DB Tubbs stated that Jowett's were obliged to go to the solid tappet valve train because the US supplier (Lockheed) could no longer supply the "zero-lash" units because their license to manufacture it was withdrawn (by one assumes the license-holder, whoever that was).

It is my opinion (with nothing to back it up) that the use of the hydraulic tappet really enabled Gerald Palmer to comfortably get away with the single central camshaft. I think that had the hydraulic tappet not been available to him when the engine was being developed, he might have been obliged to go with the much better arrangement of the two camshafts, one on either side of the crankcase as in the prewar 10 HP 4-cylinder cars. The hydraulic tappet overcomes the differential expansion issues that I discuss in my valve train article here: TOPIC

[David Kemp]

I would love to sort out the fact from fiction, but, as Jowetts met their demise 60 years ago, I think it unlikely. I dislike the belief Lockheed could not supply, as, I believe Armstrong-Siddeley continued to use this tappet. They were from what I am led to believe the only other British car company using hydraulic tappets.And on the other side of the Atlantic, within a few years every USA manufacturer was using them.
By the way ,your article on Jowett valve train was very interesting. I hope to eventually put it to use. If anyone has designed a new profile please let us all know.
Jowett warned Mr Wylie"you can change anything you like, but NOT the cam, we have spent too much time and money on it's design for you to improve" & I think it was the only engine part on the Wylie Javelin he did not tamper with. Actually it may be Mr Augustin & his racing Grey Nurse racing boat. My memory is getting cloudy.......

[Forumadmin]

Interesting article from the 1947 Lightcar.
Perspex roof?

The may issue is currently on ebay

[Forumadmin]

Hudson Service Information for the 1956 "Hornet" Special V-8 Series when used in conjunction with the Electrical Section of the 1956 "Rambler" Technical Service Manual and the 1956 Technical Service Manual Supplement.

Valve Tappets and Push Rods
The hydraulic valve tappet consists of a body, plunger, plunger return spring, check valve assembly, push rod socket, and lock ring (Fig. 4).

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FIGURE 4—Sectional View of Hydraulic
Tappet Assembly
The tappet operates in a guide bore which has an oil passage drilled into the adjoining main oil galleries.
When the tappet is on the heel of the cam lobe, the plunger return spring indexes an oil hole undercut in the plunger with the oil supply admitted through the tappet body. Oil under pressure flows into the body- through the check valve assembly maintaining the tappet fully charged.
This cycle of operation occurs when tappet leaks off some oil during the normal valve opening events. Opening movement of the cam lobe causes tappet body movement, closing the check valve and transmitting "zero-lash" movement of the push rod to open the cylinder valve.
The valve tappets should be cleaned and serviced at time of engine overhaul or whenever excessive noise exists.

FIGURE 5—Valve, Push Rod, and Tappet
Assembly
When removing the tappets, they must be kept in an order that will insure replacement in their respective operating bores in the engine because they are select fitted to that bore. Keep each tappet component group by itself as all detail components are select fitted to one another in manufacturing.
Only complete tappet assemblies are supplied for service replacement.
The tappet assembly should be cleaned in a solvent to remove all varnish or leaded deposits. After cleaning, the tappet must be "leak-down" tested to insure its "zero-lash" operating ability. Kerosene should be used for this test. Test the tappet by filling the body with kerosene and then install the plunger return spring, plunger assembly, and push rod socket. Leave out snap ring for test. Insert the push rod in tappet socket and check it for "leak-down" by pushing downward on rod.
If the tappet leaks down rapidly or collapses immediately, it must be rechecked and/or replaced with a complete new tappet assembly. The normal tappet will take approximately 10-45 seconds to "leak-down" with kerosene with a 50 lb. load, travel of .125". After testing tappets, they should be pre-lubricated and assembled in the engine without an oil charge. They will normally charge themselves in 3 to 8 minutes of engine operation.

[PJGD]

It is mildly interesting that Figure 4 above from the Hudson Hornet manual does not appear to have any means to adjust the "tappet" setting. Yes, even with hydraulic tappets you still need to adjust the setting so that the inner piston of the tappet is at the right part of its stroke when on the cam base circle.

As for David Kemp's point about disbelieving the Lockheed anecdote, it seems quite plausible to me. A little research on the US Patent Office website shows that the hydraulic tappet that Jowett sourced from Lockheed was evidently an Eaton design that was filed in March 1940 and granted in June 1941 (US2246330). Why Eaton would grant Lockheed a license to manufacture this product one can only speculate and why they would later withdraw it is not clear, but there are a number of possible commercial reasons. As for why Jowett were unable to find another source is also not clear, but it may be that the long supply line from the US may have caused production difficulties, then again the Jowett specification was probably unusual for two reasons, 1) it had to operate facing downhill which was not typical, and 2) the necessary range of travel would have been significantly longer than typical due to the differential expansion issue.

Armstrong-Siddeley may have been purchasing their tappet from a different source.

Philip

[David Kemp]

regards all tappets need adjusting, the answer is NO, a precision machined modern engine does not My old Holden 202 had no provision for adjustment,as my current Mitsubishi also does not.The benefit of hydraulic tappets is their ability to take up wear. My current Mitsubishi has 250k & never had any valve adjustment, somethings improve. This is one reason I would love to build a Jowett with hydraulics, I find tappet adjustment tiresome, & crude.

[robert lintott]

Are there Javelins around which still have hydraulic tappets? According to the Technical Bulletin no 34 and 38 the Hyraulics were changed to solid at around engine no 11907 in November 1950 . Numerically this is about 40 % through the total production of Jav/Jup engines . Hydraulics could be converted to solids but required a change of camshaft, new tappets and new push rods . In my copy of the Bulletin someone has written in the prices for these as 54 shillings for a shaft, 11shillings for a tappet---or a set ?--and 7shillings and 6 pence for a push rod --a set ? ----Happy days ! No reason is given for the change . Bob

[Robin Fairservice]

My 1950 Javelin, chassis and engine number 10100, has hydraulic tappets, and I also have a slightly later engine (a barn find in Ontario) with hydraulic tappets.

[David Kemp]

How do you find your hydraulic Javelin? Would you change to solids? Had any problems?

[Robin Fairservice]

I have had an issue with a badly leaking tappet which was replaced as it was a shade undersized, but I believe that the tappets are probably responsible for low oil pressure when hot. I looked at what was needed to replace with solid lifters, but didn't want to undertake that project as I am not a great mechanic, and there is no one over here (at least within a few hundred miles!) that could do it for me.

[Forumadmin]

Robin,
Have you upgraded to the later oil pump which gives much more volume?

[Robin Fairservice]

My oil pump was modified by Neil Moore, in New Zealand, to provide greater pressure, and the oil passage in the block was bored out to suit a larger diameter feed off of the pump. I don't know whether that means that I have a later pump.

[Nick Webster]

Don't forget that the series 3 engine had smaller oilways to the cam followers - supposedly because such a large flow was not required to the solid followers. Of course this by definition means there was probably an improved flow to elsewhere. It is said that hydraulic followers would not operate in a series 3 block and since this has the added advantage of extra stiffness (for the bearings) it has tended to be the replacement block chosen if possible when required. Therefore I cannot imagine there are many of even the older series cars capable of running hydraulic lifters. Could be an interesting experiment though if parts could be found.