Exhaust valve seat in 250 2V head question

[BKNLINE]

My machinist noted the outer two chambers #1 and #6 are shape differently than #2-#5. The wall of the chamber is closer to the exhaust valve.

Does anyone know what size outside diameter exhaust valve seat can be used and what depht it can be installed at? I think he's worried he my punch through to the water jacket.

Did anyone else notice the outer two chambers are different on their Australian 250 2V head?

Thanks in advance.

Dean T

 

[addo]

What casting - 71DA, ARC72DA or ARC74...

 

[BKNLINE]

The head has a cast in part number of ARD1OE 6049-AC
Oh, and we're trying to install the larger 1.50" exhaust valves, 1.75" intake valves.

Hope that helps!

Thanks!

Dean T

 

[addo]

That's a D1 casting. I don't have photos of one to look at! :x

The D2 head pictures seem to show a fair amount of consistency; probably less than 1/32" overall variation.

 

[xctasy]

Don't do 1.5 inch exhasts. 50 thou is enough to make an elaborate sprinkler system of your Aussie head.

Go for smaller exhast valves, buddy. 1.45". On later castings, the No 1 was very very thin on metal, according to Jimbo65 when he did his 65 200 cube 2v Mustang.

The cam has to balance the intake and exhast flow, as the exhast valves and exhast ports are the restriction on a 2V. As long as you've got 65% of intake flow on the exhast, it'll work fine. Good headers and a good exhast system will make up for the loss.

On a modern engine with unleaded fuel, you need a lot of thermal transfer. Good vlave guids, good margins on the exhast valve and keeping things stock are the best bet.

 

[addo]

The way I heard it, 1½" exhaust valves was the first mod of choice to the head proper in the "good old days". Broncobo's head had them fitted without seat inserts when my mate Dan still owned/used it.

No issues with that head at all - the WW was a thirsty carb and Dan's motor may have been a little low on CR but the top end performed flawlessly. No coolant leaks into the chamber!

 

[BKNLINE]

Thanks for the replies. I guess I better play it safe and get the smaller valves - my machinist mentioned some exhaust seat recession was evident so it'll need new exhaust seat inserts.

Bummer, I already had bought the larger exhaust valves...

Thanks again, folks!

Dean T

 

[xctasy]

Hopefully I sound concilatory here on, as I cannot yet find the darn post I saw in 2003 on this matter. :!:


I'm still going through Jimbo65's posts. Two conflict...1.55 SI exhasts were quoted as Jims final type. Could have been machined down, but 1.5" SI or Manley were initally recomended.

http://fordsix.com/forum/posting.php?mo ... st&p=41181

http://fordsix.com/forum/viewtopic.php? ... ght=#60119


:roll: I'm 105% positive that Number one exhast is critically thin on one particular Aussie 2v casting, and it wasn't due to core shift or quality assurance stuff ups, it was integral to the design.

:roll: I aditionally felt certian it was Jimbo 65 who made the comment. His machinist said you cannot go up and maintain a good exhast seat to water gallery margin for an unleaded fuel engine in modern conditions with valves bigger than 1.45. It was written back in 2003, and I took note of it.

I'll have to recheck posts by RickSmol, Offenokee Comet or other guys who had there machinist comment on it.

I have a rule with leaded heads...never, ever run excessively large valve head diameters or thin valve seats and special minimised guides on the exhasts. You can make up for any issue with flow balance by lift or duration of the custom cam grind you use.

The 2V heads could even run smaller valves on the exhasts for safety, and you can come up with some higher lift rockers on the cylinders number one and six since the 1.6 and 1.75:1 roller rockers are actually FE items, which work as 1.5 or 1.65 ratios when on the I6. Use 1.5's on everything else.

Yank head machinists are very knowledgable, and have been dealing with valve seat recession for years, while we Aussies and Kiwis have only been unleaded since 1996 or so. We tend to push the envelope a bit harder because a 2V head is easier to find here than in the USA!

 

[BKNLINE]

Appreciate the reply. I do think I better back down to 1.45 to be on the safe side. As you noted, it would be tougher to get a replacement head. I already bought the roller tip rocker assembly too so I can't juggle the rocker arm ratios. Oh well, the target HP for this engine is 200 and leaning towards fuel economy. The next 200 will use the aluminum head...

Dean T