Still trying to sort out a new cam for my 110 3.9i after the Britpart near-disaster. I see Rimmer's have genuine LR 4.2L cams for £95, which is a bit of a deal. Has anyone any experience of running one of these in a 3.9? So far as I know, it should fit fine, it's just a case of whether the grind is different and if it is, is it any good in a 3.9?
Spoke to Rimmers - they say "it may work in other engines, but Land Rover only sold it for the 4.2" - which is perfectly correct but not a huge lot of help.
Is there anywhere I can find specifications for the standard Rover cams? I've got both David Hardcastle's and Des Hammill's books on the RV8 but neither give much info on factory cams.
I rebuild RV8 engines, and I've been wondering the same thing myself for quite some time now. Rover never, to my knowledge, published the valve timing figures for the 4.2 cam, but I know it IS different to the 3.9 timing. I'm still trying to find the timings after 4 years....! Badger.
I'm almost tempted to buy one (£95 for a genuine cam isn't bad) and then I suppose calipers, a dial gauge and a degree wheel should be able to get the numbers. Do you have the numbers for a 3.9 we could compare it with?
From memory the 4.2 is a longer stroke but the same bore as the 3.9, (I think) that shouldn't effect the valve/piston clearances unless the cam is higher lift, which I doubt...
Righto, I've ordered a 4.2 cam from Rimmer's - I'm half-expecting a call to say it's no longer available, but we'll see. Hopefully it'll arrive for the weekend and I'll get it setup on some vee blocks and do some measuring.
Got the cam and it looks very nice indeed. Unfortunately we've had a slight issue with the kitchen waste coming apart under the floor, so I'm having to replace the kitchen floor at the moment, which takes priority over measuring camshafts! Hopefully by the weekend...
Righto, finally got around to doing something with the 4.2 cam. I fitted it this morning and measured it using a dial-gauge on the inlet and exhaust tappets for cylinder 1 and a degree wheel on the crank nose.
I can say with a fair degree of confidence that the lift is the same as the 3.5 and 3.9 cams at 0.4" (at the valve) and that lobe seperation is slightly greater than the 3.9 cam at 112.5 degrees.
With less confidence as I only measured lift at every 10 degree of crankshaft rotation, which in retrospect was a little too coarse, the duration seems to be slightly longer at somewhere around 300-305 degrees, the inlet opening and closing later than the 3.9 and the exhaust opening a bit earlier and closing a bit later. I'm not super-confident about these numbers as I say, and I'm a little surprised that the duration for inlet and exhaust are different - I wouldn't expect Rover to have been that clever with the cam design.
The details are available in an Excel spreadsheet at
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Anyhow, I've installed the cam in the normal position (no advance) and hopefully will get the engine running over Easter weekend - I'll be sure to let you know if it idles (or goes...) like a top-fuel dragster!
I seem to remember that the 4.2 engine was initially developed by JE Engineering. When the LSE was considered by LR as an upgrade to the existing RaRo Classic model range the factory has bought the manufacturing and design rights from JEE.
This must be a good explanation on why the camshaft is different from the
3.9 one (but then again if memory serves me right the 3.9 cam is also different from the 3.5 and this was an LR "in-house" designed job.
That's interesting to know that the 4.2 might be a JE development - it would explain why the cam is different. Badger mentioned the 3.9 cam is basically just the 3.5 cam but advanced a few degrees (which is a common trick for more low-end grunt), so that could tie-in, as the 3.5->3.9 change is not really a re-design the way that JE might do.
I spoke with John Eales a few years back about high-compression pistons for the 3.5, maybe I'll give him a call and see what he can offer.
FWIW the engine is running now, but it does spit through the inlet like an angry cobra around 2000rpm. I'm hoping this is because I've not set the ignition timing yet (can't find my timing light) and not the cam...
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