Hardened Seats and Guides

[RJS]

Hi All,

Curious if anyone may know the answer. The PO on my car had the cylinder head rebuilt in 1994. 8 new valve guides and 8 new valve seats were installed. But, I do not know the source or make of those parts.

What is the likelihood that they were hardened for unleaded fuel back in 1994?

Thanks,

Bob

 

[TR4nut]

I'd say a very good chance, if not 100%. Leaded gas was phased out completely by 1986, by 1994 I think you are dealing with hardened seats.

 

[TR3driver]

Pretty good, I'd say. The need for hardened seats was recognized way back in the 70's.

But it almost doesn't matter; either way there is no sense in replacing them again or using a lead substitute unless you start having problems with recession.

And it's easy enough to tell when you're having recession. When it starts idling rough, and a minor tune-up doesn't fix it, and you check the valve lash only to find that one or more exhaust valves are too tight; that's valve seat recession.

 

[RJS]

Much appreciated and good to hear.

As you say, either way, I would not pull the head simply to replace them with confirmed hardened parts - unless I detected a problem. My understanding is you have to drive really hard for valve rescission to set in. And I'm not driving my car that hard.

Bob

 

[CJD]

I've never heard of a non-hardened replacement valve seat...even in the '70's. The installation process pretty much made hardening necessary. I think you'll be good!

John

 

[Don Elliott]

In May 2000, the valve gaps were getting tight every 500 miles. So it was time to have inserts put into the head. My 1958 TR3A had been driven 43,000 miles since I re-built the engine in 1990 with the original head and most of the original valves using lead-free gasoline during this 10-year period. The guides were the original ones too.

So in May 2000, I took the head to an engine shop and had him put in his own new valve seats for the 4 exhaust valves plus 8 new guides and 8 new valve guides that I suppplied to him.

Since then, I have driven another 64,340 miles without having to re-gap any of the valves more than a thou (0.001").

The only problem I have heard about new valve seats is when a shop does not intall the seats prperly. This happened to a friend with a TR3A where one of the inserts dropped out of place in the head and "collared" the valve as shown. He was lucky, because this happened while backing his car out the garage - not at 80 MPH on the highway.