Head pre cup question

[tom yuenkel]

I am interested in knowing how hard is it to change precups from one head to another? and does the head need resurfacing after the swap?

[tom yuenkel]

the reason I ask is I have a replacement military engine (1987) being sent to me and this time it's going to be torn down and inspected and Enlight of the recent articles about economy and precups I wanted to combine better heads with smaller precups. I'm hoping to use my original heads off my 1991 6.2 na currently because I'm under the impression these heads flow better, sound right? I would like to install the smaller precups off the 87 heads into the 91 heads combined with port matching. I know from running the first 87 engine for 10000 miles I was getting consistantly 18 to 20 mpg with a high of 21 when I slowed down to 65mph. What I don't know is if after changing them does the heads require resurfacing?

[john8662]

You can swap pre-cups from one head to another if neither of the heads have been re-surfaced. Most machine shops surface the heads by leaving the cups in the heads, so they get shaved too, under that circumstance you can't swap out the cups, unless you ream the inside diameter of the precup chamber to accept a standard size cup. There is a special tool for this, The Diesel Depot, a Diesel Page vendor uses this technique and can do this if necessary.

The '91 heads are better in respect to injector angle, they will allow the engine to start better in the cold, not sure on efficientcy. I'd leave the cups that are in the '91 heads in the '91 heads due to the changed angle, may not be a problem though.

Others have installed 6.5 Turbo cups in early 6.2 heads and have had no issues...

Ditto on inspecting this one, a fresh set of Fel-pro head gaskets will ensure good service with the turbo.

J