Camshaft question

lyons · Post by **lyons** » Sun Dec 21, 2014 2:49 pm

Reading a previous question by Pauk J. about identifying parabolic camshafts there was a reply from Christopher Storey stating that although it is possible to use 2 hole sprockets with 4 hole camshafts, it was NOT possible to fit 4 hole camshafts to 2 hole sprockets.

If not - why not?

Why not fit a new 4 bolt cam gear coupler if required ?

Can someone clear this up as my option is to fit available 3.8 S type (4 hole) cams in 4.2 xj head. (2 hole )

christopher storey · Post by **christopher storey** » Sun Dec 21, 2014 3:41 pm

You can fit any cams in any head. What you cannot do safely is mix and match the cams and sprockets i.e 2 hole cams need 2 hole sprockets etc

lyons · Post by **lyons** » Sun Dec 21, 2014 5:02 pm

Christopher,
Thanks for your reply - I understand

Just for my knowledge - why can't the cams and the sprockets be mixed.

Are the holes out of alignment or is there another reason ?

PeterCrespin · Post by **PeterCrespin** » Sun Dec 21, 2014 6:11 pm

They can be mixed. The only ones to avoid are the verniers with 4 cut-outs around the periphery (thereby reducing the number of teeth in engagement. No idea why they did that.

Obviously you can't use 4-bolt paired lock tabs on 2-bolt cams so if using two bolt anything you need lockwire cam bolts which are NLA I believe?

Pete

christopher storey · Post by **christopher storey** » Mon Dec 22, 2014 9:15 am

The words I used were cannot be mixed safely . For the reason Peter suggested, that the later variety with a low number of vernier teeth tend to strip the vernier very easily

Post by **mgcjag** » Mon Dec 22, 2014 9:24 am

Hi Lyons......have a look at this info on Cams it may help ....Steve

http://www.georgiajag.com/Documents/Camshafts.html

lyons · Post by **lyons** » Mon Dec 22, 2014 10:43 am

Thanks for all replies. A little knowledge is a wonderful thing.

Intention is to use 4 hole verniers (without cutouts) on 2 hole 3.8 S' type cams to be able to drive tacho on 4.2 xj6 head on 3.8 block.

If not then use original 4 bolt cams with electronic tacho as a reserve option.

PeterCrespin · Post by **PeterCrespin** » Tue Dec 23, 2014 1:01 am

lyons wrote:Intention is to use 4 hole verniers (without cutouts) on 2 hole 3.8 S' type cams to be able to drive tacho on 4.2 xj6 head on 3.8 block.

If not then use original 4 bolt cams with electronic tacho as a reserve option.

In your opening post you said:

"Reading a previous question by Pauk J. about identifying parabolic camshafts there was a reply from Christopher Storey stating that although it is possible to use 2 hole sprockets with 4 hole camshafts, it was NOT possible to fit 4 hole camshafts to 2 hole sprockets. "

That was you saying the same thing twice, merely in opposite sequence.

Then you said:
"Can someone clear this up as my option is to fit available 3.8 S type (4 hole) cams in 4.2 xj head. (2 hole )"

Now you're saying (above) 2-hole 3.8 cams - which is the first statement I can actually believe.

I don't know what it is that needs 'clearing up'. I think that in this thread you have received all the relevant information there is, for whatever swap it is that you actually go ahead with. The good news is, that as far as cam drive goes you can't easily screw up. The tach drive and tach mountings on the back of the head can be made compatible if they aren't already (e.g. the XJ head is not normally drilled for a tach generator).

Pete

lyons · Post by **lyons** » Tue Dec 23, 2014 12:20 pm

Peter,
Sorry about all the confusion !!

However I had no previous knowledge of NOT being able to mix 2 hole and 4 hole cam drive verniers.

The good news is that in my box of bits I have a set 2 hole verniers that I can use along with locktabs and drilled bolts.

P.S. When did the drilling of tach drive holes stop. as my head is already drilled.

PeterCrespin · Post by **PeterCrespin** » Tue Dec 23, 2014 1:17 pm

lyons wrote:The good news is that in my box of bits I have a set 2 hole verniers that I can use along with locktabs and drilled bolts.

No you can't. Lock tabs are for 4-hole cams, they cannot be used on two bolt cams.

lyons wrote: P.S. When did the drilling of tach drive holes stop. as my head is already drilled.

The head may be drilled but is it drilled for a tach generator? From about 1968 all Jags dropped the AC tach and went electronic. The heads were drilled for a two-hole end plug. The tach generator holes are different although I think there was an interim 3-hole blanking plug to allow the newer heads to be used as service replacements on older cars. By Series 3 XJ ten years later they had abandoned all drilling and switched to a half-moon rubber plug and flat can covers with continuous gaskets.

jagwheels · Post by **jagwheels** » Tue Dec 23, 2014 1:57 pm

Hi Peter where did they fit the electronic tack on S3 XJ engine and could it be used instead of the AC tack that goes on the cams

PeterCrespin · Post by **PeterCrespin** » Tue Dec 23, 2014 5:58 pm

The electronic tachs run off the coil supply (Series 2) and impulse lead (Series 3 E-type and XJ. You need no cam generator.

I fitted the guts from a dirt cheap S3 XJ tach inside the E-type 5" casing and got a tach that way when I fitted an S3 XJ engine and ignition into my S2.

jagwheels · Post by **jagwheels** » Wed Dec 24, 2014 3:20 pm

Thanks Peter I will look in to doing that with mine

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