Greetings all,

Due to low compression on #5 (135psi cf. 150-160 on all the other pots) I have decided to swap the cylinder head on my 1964 3.4 with the later straight port unit off a Jag 420. From my "research" I believe this is a common modification.

Has anyone else done this & any traps for the unwary (that's me!)?

I note the intake manifold needs to be swapped and the accompanying water intake pipe. Seems the carby ports are sized for HD 8 (2" jugs, which I don't have), so I'm assuming the HD6's will still be OK (same bolt pattern), notwithstanding.

Any ideas or tips would be gratefully received.

Cheers.

Peter.

 

Given the dearth of replies, nevertheless I will progress with this mod. and report further in due course.

A real learning experience so far. As the inlet manifold is different, so is the water outlet pipe and a further bit (thermostat housing) is required. Another $250 from the wallet.

You can never say working on Jags is boring.

 

Sorry I can't help with any advice- but thanks for sharing your journey!

 

My 340 is all in pieces right now as far as the intake manifold is concerned and it has the later straight ports.
I can take some photos, but I'm not sure if that will help.


Shouldn't make a difference on the carbs, but the later design had the external starting automatic choke extension and the intake manifold had 6 ports to enable fuel flow for this propose.
If your current carbs are manual choke , then you will have to plug these ports off.

 

Thanks Jeff,

When I purchased the 3.4, a lot of other parts came with it. Sort of a "package deal" you might say. A lot of junk, but some good bits too.

Included were two manifolds, both for 2'' SU's, one with the 6 "enrichment device" ports (underneath), the other without. So I have come to the conclusion the 1st is off a 420 model, the other a Series 1 XJ6.

So as I have the HD6 carbs with the Mk 2/420 enrichment device it seems now that the 420 manifold is the one to use, as I don't have the later 2" XJ6 carbs.

Thanks for confirming the manifold mystery.

The new water outlet housing (GBP80-ouch!) interestingly has a bleed tube fitted at the top. Barretts tell me the bleed valve that attaches thereto is NLA.

Yet another interesting Jag Mk 2 drama!

 

“Includedwere two manifolds, both for 2'' SU's, one with the 6 "enrichmentdevice" ports (underneath), the other without. So I have come to theconclusion the 1st is off a 420 model, the other a Series 1 XJ6.”

This made me curious. Ihave a 1960 3.6 with SU carbs and an electric choke. That choke empties into what I would describeas “6 ‘enrichment device’ ports underneath”. My 67 3.4 has the same setup.

So it sounds to me like youhave the correct parts for your 3.4 and the manifold without the ports might beeven older.

I can send pictures as I have all the parts on a shelf.