6 replies to this topic

[eric67]

My local machine shop is reluctant to fit hardened exhaust valve seats to my 12G295 head as they don’t have the specialised freezing equipment that they consider necessary to freeze the inserts prior to insertion. However, from what I have seen on the internet they can be simply pressed in at room temperature.

 

I’m guessing that the cast iron head is more stable than the hardened insert so in operation the insert would expand to improve the fit?

 

Can anyone confirm whether this is a satisfactory engineering procedure, and/or does anyone have any horror stories of failing inserts…

 

Many thanks,     Mark

 

 

 

[dyshipfakta]

Just reduces the risk of cracking the head is my understanding. They may not wish to attempt it without doing everything possible to reduce the risk.

[Hpal]

They should be able to get hold of some liquid nitrogen to do the job. Or at least some dry ice which should freeze the inserts down enough to drop in. They can measure the insert diameter at room temp, then freeze it down with dry ice and measure again to get how much it shrinks and machine the recess to suit. Dry ice is readily available. Alternatively, dont worry about the inserts, just use a valve additive in the fuel.

Edited by Hpal, 08 December 2021 - 09:52 PM.

[Spider]

I did a 295 head only a couple of months back. I used Rover Inserts and just pressed them at room temperature, 0.0035" Interference fit.

In operation, the seat is going to run much hotter than the cast iron around it so they'll only get tighter. You don't want to fit them with too much interference as that can - over time and heat cycles, cause the cast iron to relax.

[eric67]

Thank you for your comments.

 

3.5 thou interference does seem like quite a tight fit but good to hear first-hand experience that the the inserts should fit at room temperature without cracking the head.

 

And for reference, I have found a detailed guide to fitting valve seats on the Dura-Bond website which I will supply to the machine shop. I’m hoping that they will accept this as a proven method and undertake the work to save me looking elsewhere.

 

Dura-Bond Valve Seat Inserts Info. (dura-bondbearing.com)

[Spider]

When you see your machine shop guys, if it helps, pass this factory info on to them;-

 

 

[eric67]

Many thanks. This is all building evidence that press fitting valve seats with a .0035” interference fit is an acceptable and well proven engineering practice.