Technical Do valve seats have the interference built in

I just installed my first valve seats today but had to match a head that was already cut to 1.625, so i trimmed the ones i ordered down a bit to 1.629 - why would a shop previously have cut the pocket to 1.625 when it seems common valve seats come in at 1.625 - shouldnt they have cut it to say 1.621 or 1.620?

This is an industrial GM inline 4 engine with 1.6 exhaust valves

 

Valve seats should be but in a freezer before install and staked.

 

Some shops pack them in dry ice for a few hours before they install them. If you don't have that interference fit they will get loose. I'd check with the manufacture of the seat to see what they suggest though.

 

all of the seat i have done the cutter was a common size 1.5 1.625 1.687 ect and the seats had the press built into them. for your 1.625 bore the seat should have mesured 1.629 to 1.630 the also make over sized seats

 

There's no such thing as..."built into them". The machinist has a seat, HE...makes the fit.

Cast iron and aluminum have different interference fit requirements.
Some shops us more interference than others.
Depending on the seat dimensions, this can affect the interference. Thinner cross section seats require more squeeze to stay put under the stress of racing / high performance heads.

A couple of shops that I've worked with use more than normal, because they are older shops and have seen...things !
.0004" to .0006" interference is not uncommon.

Mike

 

Part Number SB1625-1 (Valve Seats)


Specifications

Type

Data



Angle 45
Depth 7/32
Exact O.D. 1.6300
I.D Top Taper
I.D. 1-3/8
O.D. 1-5/8
Ovs 005,010
this is the seat i would have used notice the size in the part number is 1.625 and the actual od is 1.630. there are books and tech sheets that could go on for days with all the manufacture and material differances and instalation procedures. but the basics for cast iron is the cutter will be a standard size and the seat will be oversized from that by the manufacturers recomended press if I was in dought i would call sbi they make this seat and had a good tech guy the last time i called.

 

ok thanks - i read the description of some seats and there is about 4 thou built in - much appreciated! I did install them with the van norman driver and a mallet and high temp red loc***e- they are snug trust me!

i was thinking of staking as a fail safe so thanks for confirming that- worth it