Building a 42x36 AMC Head - Who Has Tips?

[Patrick1984]

Hi,

I've got a 73 bus with a camper conversion that has a CJ in need of a rebuild. I pulled it down with no compression on one cylinder due to a triangular exhaust valve... I also found the bores are polished so are planning on doing a full rebuild. I'll be keeping it mild with Mahle pistons and cylinders, AMC heads and a new 914 spec Webcam. Compression will be around 8:1 as I'm in Australia where the summer hits 45 or 113 whichever way you look at it. I’m thinking I should up the 39x33 valves to 42x36 if it’s not too huge of a cost. Can anyone advise whether I can do this with the standard AMC seats? If not what seats should I be using and who does good quality valves? I spoke to one machine shop who wanted $3000 and came across as hesitant then I spoke to another who I’ve used in the past who quoted $5-600 and didn’t seem phased. Apart from bigger valves and a 3 angle port job is there anything else the AMC heads want on a low power build like this? Am I wasting my time going bigger valves on such a standard build? I’m just hoping to up the torque and keep it strong to around 5000rpm. Induction will be rebuilt standard PDSITs and exhaust is heater boxes and standard muffler. Only other mods is a T3 WBX electric ignition with the T2 weights. I’ll possibly go to a proper extractor depending on how hot it runs and the power it makes.

Any advice is appreciated. If you need to know more let me know.

Thanks,
Patrick.

[wreck]

Where in Aus are you mate ? I’ve a good friend ,John Alder , Volksengineering , he has had AMC seats throated out to fit 42/36 valves .he is also very good with making type4s last in our hot weather .Based in Brisbane .

[Patrick1984]

I'm based in Sydney but happy to have a chat to someone local whos done it before. Postage might be a killer. Can you pm me his details? Thanks, Patrick.

[wreck]

PM sent

[cal 67]

Port to 85% of the valve size, which is only about .7mm larger than the port is already. Blend the ports to the seats, and use a bore gauge to make sure the port is fairly concentric all the way up to the flange. Same goes for the intakes. No less than 35.7mm. On the exhausts, just aim to streamline that guide boss and taper the protruding portion of the guide.

[Patrick1984]

That's great info. Thanks. From what I can gather I'm best to just take the valves out to 41x34 using the AMC seats. Anyone have any specific recommendations to give the machine shop as far as what valves to use or angles for the seats? or otherwise? Is there any reason not to use the AMC seats? I can't find any real current info for that. Just a lot of old info on failures.

[GARRICK.CLARK1]

I bought my 42 x 36 stainless valves and the valve seats from EMW, any good VW machine shop will be able to fit them to some new AMC heads, its nothing to worry about.

[wreck]

I got SI valves from the internet .http://www.sivalves.com . They have been in use for a 6 years with no issues .

a 3 angle valve seat cut would be best . Someone else to contact is Wayne Penrose . he is also a type 4 guy in Australia and may have valves in stock . http://www.wpvw.com.au/WPVW%20family.htm

Wayne owns and drives this weapon .Turbo type 4 . https://www.youtube.com/watch?v=ERAqq6zd1d4