1976 280Z valve issue

[SCPMAN148]

I have installed new valve guides in the head and now the valves won't fit through them. They fit before they were installed. Does anyone have any ideas?

[Phred]

Hi, and welcome. Your issues with the guides are common. First, the reason they fit befor install, and not afterward: Valve guides are an interference/ press fit in the head. Generally, guides should have a minimum of .0015 press fit, with no more than .0025 interference. Depending on the type of guide material/alloy, the valve should have a clearance min. of .001/.0015 for the intake, and .0015/.0025 on the Exhaust. So, when the guide is installed in the head, the I.D. of the guide shrinks almost the same amount as the press fit. Furthermore, the installed guide will have a pronounced taper on the I.D. The guide I.D. will be tighter in the area of the press fit. So frequently you may be able to start the valve in the top of the guide, but sticks when the valve gets down to the area where the guide fits in the head. this is not a good situation, as the valve guide I.D. should be as straight as possible. Reason: the valve transfers heat to the guide/head through the guide contact, and the valve seat. So after install the valve guides need to be either reamed, or honed to straighten the guide and provide proper clearance. Also if you installed the guides with a driver and hammer, the top of the guide will have the I.D. mashed down a bit, which can also be fixed by the reaming/honing operation. Take your valves and head to the best engine shop you can find, and have this work done. There are some hacks out there, so do yourself a favor, and get the best shop you can to do the work.

Trust me, I'm old, and have been doing this stuff for a very long time. Cheers.

Phred

[beandip]

Phred, WOW, I haven't seen a post from you in a vary long time. Glad to see you are still around here.

Gary

[SCPMAN148]

Thanks for the advice. I will do what you suggested.