Hi.

I recently purchased an '85 XJS HE. It had a head problem that the previous owner had quoted to repair. The mechanic said the head would have to come off to be fixed. The owner said it was a broken valve spring/dropped valve....but I suspect (after reading through several forum posts) that it is a valve seat that has dropped.

I located another set of v-12 heads but the gentleman that has them isn't sure of the year/model of jag they came off of.

How do I identify if these are the correct heads

Are there casting numbers that I can go by or some obvious feature that I can inspect

As I understand it the HE engine ran over 12:1 compression and the earlier engines were about 10.5:1

If there is some visible feature that differentiates these heads pictures would be greatly appreciated.

Thanks

David

 

The earlier, non-HE engines had the combustion chamber in the pistons, The head face was flat with the valve seats and valves on this flat surface. The HE engine, (from around 1984 was it ?), has the combustion chamber partly in the pistons and partly in the head. One of the valves is recessed into the head with a small "ramp" up to it to allow the "Fireball" to form.

 

Thank You Fraser.

David

 

Actually it was 1981 that the combustion chamber was put in the head and shrouded. A quick and dirty way of telling without looking up a bunch of numbers ( and assuming the heads are still on the engine) is to pull a easy to get spark plug. If it’s got a washer on it chances are it’s the Flathead if the plug seat is tapered it’s the later head.

 

MG this thread is 10yrs old, comon get real?

 

I guess I should start checking dates before I read the subject.
thanks and sorry to bother you

 

MG, NO problem i have done the same once in a while!

 

I wonder if David got a email saying he got a response from his question?

There was one thread that I replied to because it was on top of the list - just trying to be helpful. But it turned out to be a very old post - not sure how it got to the top.

So sometimes interesting things happen

Cheers
Steve

 

Yes. I did get an email even after 10 years. I got a complete engine and also a complete 2nd car a little after that. I think I will need to retire just to get working on all these back burner projects that have collected at my shop.

david

 

Who knows what lurker finally got his question answered either. We need to remember that new people are buying these cars all the time.

 

I still get emails from the forum. I ended up getting a complete engine and also a 2nd car. I think I need to retire just to have some time to work on the projects I have gathering in my shop. I saw a very interesting DOHC supercharged v12 build online.

David

 

David,

Your two recent posts were automatically locked for moderation - probably because you are an infrequent poster. I've unlocked them now.

Graham

 

back to an easy way to tell flat cyl. head, VS and HE chamber head , one has the sparkplugs at an angle , other has plugs coming straight out!
altho i forget which is which ,Darn?
ron