Cylinder Head q's...

[Bleyseng]

I as understand it, the "sintered" metal seats from VW ( meaning some sort of powdered metal) have a less than ideal expansion. Len uses a different metal that has a "better expansion" characteristic than the OEM VW seat. Meaning it heats up quicker to stay put in the aluminum head vs falling out as the OEM 2.0L heads were prone too. The 1.7 heads didn't have this problem in big numbers but the 2.0l did right off the showroom floor. Back in the day, my friends brand new bus had this happen driving to a vacation spot. Old time VW Dealer mechanics have detailed this "syndrome" and VW's problems with it.
VW couldn't figure out how to enlarge the 1800 engine for more hp/torque. Porsche engineers did for the 914 as Porsche had to delete the 914/6 due to VW charging too much for the bodies (long story) after Nordoff died. VW jumped to utilize the Porsche 2.0L parts for their 2.0L I think without much testing. The 2.0L 914 came out in 1973 MY after a frenzy to get it done in time. VW came out with the 2.0l in 1975, right? It was a problem for the 2.0l 914 too!
Yes, I agree that loose vac hoses, etc just poor maintenance is the cause of many dropped seats but still it shouldn't happen with the proper engineering in the first place!

[Amskeptic]

I as understand it, the "sintered" metal seats from VW ( meaning some sort of powdered metal) have a less than ideal expansion. Len uses a different metal that has a "better expansion" characteristic than the OEM VW seat. Meaning it heats up quicker to stay put in the aluminum head vs falling out as the OEM 2.0L heads were prone to.

This is making little sense to me, sorry.

The hottest place in the head is the exhaust valve seat. It is what is transferring the valve heat to the surrounding aluminum. It is the source of the greatest heat. The aluminum expansion cannot "get ahead of" the heat generated by the seat.
So any dynamic expansion expllanation you are given, I do not get. HOWEVER, I sure as hell get everybody and their brother running their new VW bus engines painfully hot and lean and the All The Time In The World VW seats, and the Even Quicker Special Seats over-expansion will indeed press the aluminum outward and THEN when everything cools, the seats are loose. Sure. But I blame the heat brought on by emissions requirements and the fact that dealer mechanics were forced to set the lean mixtures that I would refuse to drive with today, and finish off with sloppy fast dealer work as they were watching sales deteriorate.

A specialty shop who uses high quality seat material and by God follows the correct thermal and interference directions yes, I expect good results with the mixtures we can run. I would love to see a patterned thread cut in the outside perimeter of a pressed in seat, like those big nails in wood, and let the seat lock into the aluminum without staking the outsides, a practice i do not trust.
Colin

[72Hardtop]

Haven talked to both Len and Adrian with regards to the AMC heads/internals they both use the same replacement parts (valves, seats, springs, guides, keepers etc...) Len stated that the AMC head castings hands down are better than any OEM head VW put out. He said they have more material around the exhaust area as well as underneath the chambers which adds strength to the heads. As for the seats both Len/Adrian use a IIRC (tool steel seat) that is better suited for use in the VW heads. They also do not stake the seats in nor do they heat they heads up for installation. The specifc process is a trade secret.

One will never get 100% reliability with 30+ year old castings. One big reason why Jake/Len don't touch old castings anymore. Putting new upgraded parts in a 30+ year old head will yield less than favorable results. Adrian still offers the 'option' of rebuilding old heads but will agree they are NOT the same as new upgraded AMC heads in terms of reliability.

[Bleyseng]

I have yet to try it but Len has said on OEM VW type 4 head heated to 450F in an oven the seats will fall out when flipped over. Don't know how long you have to leave it baking in the oven either. Maybe I'll give it a try in a week or so when I am in Seattle for a brief visit for fun.

Len has posted pics of OEM heads and AMC heads sectioned so you can see for yourself the extra meat added in the new castings making them better than stock.

[SlowLane]

I would love to see a patterned thread cut in the outside perimeter of a pressed in seat, like those big nails in wood, and let the seat lock into the aluminum without staking the outsides, a practice i do not trust.

Umm, but wouldn't such threading or knurling have the effect of reducing the contact area between the seat and the head, and thereby reducing the effective heat transfer?

As far as sintered seats go, I'm not sure that VW ever used them in our engines. A friend of mine had a sintered seat fail in his mid-90s Ford Escort. When we took the head off, there was no seat material anywhere to be found. The sintered seat had returned to the powder from whence it was formed. In every story I've ever heard of dropped valve seats in a Type 4 engine (including both of my own), the valve had definitely dropped out of the head pocket intact. I've not heard any stories of valve seats disintegrating.

[Bleyseng]

The seats I have had in my hand from falling out have always been the intake seats. They just look like metal to me but the VW literature says "sintered metal" so I pass that along. "Tool steel" sounds better to me especially if the seats pass the 500F oven test!
But its not just the seats that make for a long lasting heads, correct in spec valve springs and other factors do.

[Amskeptic]

I would love to see a patterned thread cut in the outside perimeter of a pressed in seat, like those big nails in wood, and let the seat lock into the aluminum without staking the outsides, a practice i do not trust.

Umm, but wouldn't such threading or knurling have the effect of reducing the contact area between the seat and the head, and thereby reducing the effective heat transfer?

Not as I envisioned it. It would increase the total contact area, the thread area is like pleating. I had envisioned the above as forcing metal displacement into the thread grooves as you pressed in/rotated the seat 10* or so.

As far as sintered seats go, I'm not sure that VW ever used them in our engines.

VW was proud of their sintered seats.
I have occasioned across some soft ones, but never have I dropped or disintegrated one, and I do drive my heads in 120+* at high speed for hours and hours. I will be punished this summer, terribly, for all this cocky talk. That Type 1 engine is probably going to grenade in Stovepipe Wells.
Colin

[Amskeptic]

The seats I have had in my hand from falling out have always been the intake seats. They just look like metal to me but the VW literature says "sintered metal" so I pass that along. "Tool steel" sounds better to me especially if the seats pass the 500F oven test!
But its not just the seats that make for a long lasting heads, correct in spec valve springs and other factors do.

That is where the cool intake charge works against a tight fit.
It would seem to me that oven hot heads at 400* with an interference fit press of a well-chilled seat would exceed any field condition forever.
Colin