Thrust bearings

[David Kemp]

Does anyone have a picture or diagram of the New Zealand thrust bearing modification?
I have read the technical notes but can't visualise the procedure.
My engine is close to assembly, with crank machined, heads done & new pistons.
Are new lifters available? Mine are all rust stained, which I don't want to put on a freshly ground cam.

[Srenner]

Bill Lock has new lifters. Check the three cam journals to be positive they are not undersize.

NZ thrust mod: machine a circular recess in the assembled case halves both inside the motor and outside at the rear main bearing housing area. The depth of the recess needs to accommodate the thickness of the thrust and the clearance (.004" IIRC). Then drill the thrusts, transfer those marks to your cases, drill and tap. Screw thrusts in place.

A competent machine shop can do this or you can make your own hand crank cutter. I'm currently travelling, so can't post up pictures of mine. When I described my crank to the machinist I use, He exclaimed, "Are you trapped on the island with Skipper and the Professor?" So, the tool as now known as the Gilligan Mill.

The Gilligan looks much like the hand crank for the motor. Roller bearings act as the centering and truing guides for it. A cutting blade juts out perpendicular to the shaft. I had the machinist mill the hole for the tool to be certain it was true and square to the shaft.

The Jowett factory machined the center main on the race motors this way and fit the thrusts there. I believe Dennis Sparrow also did them this way.

[Keith Clements]

A quick search on JowettTalk, gives the Australian version.
No doubt there are others. I have done this on two of my engines.
viewtopic.php?f=6&t=5311&p=41751&hilit= ... ngs#p41751

[Nick Webster]

Must be something in the air - several folk seem to be rebuilding engines.

Recently I decided that I really should assemble as many of my separate spare parts into complete engines. One of these was one that I had rebuilt myself circa 1980. Despite probably not doing over 10k miles it had ended up in a Javelin now unused for at least 30 years. At the time I queried the strange engine number on the front plinth - GM 17 - and was told by the then club technical officer that this was an engine reconditioned by George Mitchell, also identifiable by his modification to the rear bearing to use a lead copper main and separate thrusts. In this modification only one crankcase was machined with a recess inside and out. The two semi circle thrust washers are prevented from rotating by butting to the other side crankcase and as is conventional in many engines, un-fixed in their housing and retained by the crankshaft itself.

I decided that given the length of time the engine had been out of use it should be stripped down. It did not turn over on the handle and as is my way I was not about to use brute force. I discovered that one valve had stuck and also one piston had to be carefully oiled and prodded before it would move. More to the point was my expectation that the bearings would have suffered from so many years standing uninhibited so this meant splitting the crankcase. Sure enough the bearings did not show any signs of mechanical damage, or even that they had rotated. Rather they were a perfect dull matt grey and yet not perfectly smooth to touch, which is a sure sign of acid attack. The surface did not look very good through a magnifying glass either. A bearing in this condition may run well for a while but ultimately will break up in much the same way as a potholed road surface. Apart from this , all things considered the engine was pretty good with absolutely no wear on the nitrided crankshaft. Just when I was thinking I would get away with only a new set of bearing shells I found a crack where one of the studs fastens in the crankcase.

I do however have a very good crankcase to hand in original rear main condition and so elected to transfer everything off the other engine to this one. Using an old spare rear main of appropriate -020 thou undersize and standard width I lowered in the crankshaft and measured the thrust to find it was huge at .012 thou whereas it had been fine in the other engine with separate thrusts. Consulting the Jowett handbook I noted that an over width bearing had been available for just such eventualities but although I hunted through my black museum of bearings I could not find one that was not standard width. I have contacted JCS to see if oversize bearings are to be had, but no news yet and my impression gained was that the white-metal rear bearings are tricky in general. It is a pity that there appears to be some uncertainty regarding bearings since availability is a big factor in deciding which parts, such as slightly undersize crankshafts are suitable for re-use or merely scrap.

I sorted out another crankshaft that would require regrind before use and tried this in the same crankcase. This was not absolutely accurate because owing to a different journal diameter I used different test bearings, though the thrust width measured the same. This gave only .0015 thou thrust - pretty much perfect. Pity about the journals!

So with my aspiration to build more than one engine fading I am now potentially faced with a longer and more expensive job. To get even one will involve either getting the other crankshaft ground and nitrided or the cracked block repaired. The former action still hangs on bearing availability while the latter action rather fill me with dread since there is no way of knowing how much more damage might occur in attempting to remove studs.

[David Kemp]

Thanks for your replies, my engine is being made of the remains of at least 9 other engines.
Unlike many club members I started late collecting parts, which means my base is pretty low in quality. I am using every one else cast offs.
The advantage is I am not saving any thing as usable, everything is being reconditioned.
Below is the lifters I have. Two different types! Which is the good ones to use , as I have not got 8 of either.

lifters.jpg

[David Kemp]

Does Bill Lock have email? Or Website?

[Keith Clements]

Are you a member of a Jowett Car club? I think so. How about the membership list. He is a member of all the clubs!