Greetings All,
New to this forum and looking for parts suppliers so I can fix mine. Need to do the heads and plenum butterflies- one broke and was swallowed. So far from the local dealer this looks hugely expensive. And from aftermarket local, only NAPA has any 3500dohc parts.I can handle the machine work and or assembly,but then sometimes its cheaper to deal with a great shop and just exchange cores. Minneapolis area.Any help greatly appreciated. Thanx.

I dont know,
but I think the butter fly valves can be removed/eliminated
think that's what I read on this board.

do a search here, because this sounds like something that has been covered.

If you need a different head then
"car-parts .com"

The heads are the same as the 3.0 DOHC so parts for them should not be an issue.
Remove the butterflies and shaft and plug the end hole.
How are the pistons? Did the fragments jam into one or are they just dented?

I have wondered on this and and not tried to find the answer. So does that mean that if a guy had a higher mileage 3.0 SOHC and needed to redo the heads, he might consider redoing a set of DOHCs instead? Hypotheically speaking of course...

Or are there water passages and the like that are different?

[/hijack]

There are quite a few differences between the two. I do not have much time inside a SOHC 12V engine but Frank has been heavy into his SOHC project and has the DOHC heads sitting there. Seems to find the oil passages to be different.
The 3.0 DOHC engines do not draw much money from the importers and can cost less than a proper rebuild of an existing engine. Obviously the engine support is much different and will need to be swapped. As in wiring, water hoses etc.
There has not been a production RWD 3.0 DOHC so the proper water outlets will need to be fabricated.
I am going through this now on a car I am building.

Sorry, I should have been clearer. The hypothetical is my 95 which is the 3.0 24V SOHC. I think the 24V 3.0 is far more similar to the 3.5s than it is to the 12V 3.0s.

It you took off that intake plastic cover of our 98 where it says 3.5 24V, you'd almost have to look real close and know a little to tell they were different.

I've always wondered what else is different from my motor versus the 3.0 24V DOHC that the Diamante and 3000 got. (I'm assuming they were the same to each other.)

Ahh, now that is different. Yes you can put DOHC heads on that. There are at this time 4 series of 6G7x engines.
1&2 are the G72 series and the G74 DOHC, 3rd being the SOHC 24V engines up to 2001. And the 4th being the SOHC 24V after 2002, The Sport being excluded since it remains a 3rd series till the end of it's sales here in the States.
For what you are looking at there will be two difficulties to figure out.
One is the timing belt, The conversion I did with the tall block uses the 3.0 DOHC belt. This is due to the tensioner being moved further to the passenger side on the 3rd series engines. In your case it will be a low deck engine being converted. We would need to research the belt issue a bit.
The second is the water piping at the rear of the heads, the orientation of the fasteners is different so your existing parts will not bolt to the DOHC heads. I expect a work around could be developed pretty easily.

To add to this, your 3.0 SOHC 24V engine is quite different from the Diamante / 3000gt engine prior to 1996, After 96 the 3K kept it's 1st series engine but with the shift of Diamante production to Australia it then was fitted with the 3rd series engine. This does not mean parts swapping can not happen.

I wasn't sure if it was a coolant or oil passage that concerned me, so I grabbed a DOHC head and put a SOHC head gasket on it - you can see that with the exception of some of the SOHC oil return holes between the bores, everything appears to line up:

It looks like the holes I was concerned about are water passages, not oil - if you look toward the right edge of the head, there are small passages that appear to go up above the combustion chamber and you can see that they're blocked by the SOHC gasket.... perhaps they would work if DOHC gaskets were used:

Here's a better picture of the small passage:

The small holes seem to be connected to the same chamber as this flange opening at the rear of the head:

Also, note the triangular/tear drop shaped insert that is fastened with a screw - the SOHC head also has one of these, but IIRC, it's at a different location. I don't know what purpose it serves - perhaps a plug of some type:


I've kept these DOHC heads to try to learn more about them after I finish my current project. About all I know so far is the twin cams and sprockets make them nearly twice as heavy as the SOHC head. <img src="/forums/images/graemlins/scared.gif" alt="" />

I wouldn't want to put these on a 12v SOHC engine until I knew a lot more - also, there's no distributor provision, so the ignition system, ECU and harness would have to be changed.

Frank

The small internal water passage is to cool the divider between the exhaust valves.
The screw head is the drilling of the oil passage feeding the head. As you can see the DOHC heads have 4 longitudinal oil passages, much more complex.