View Full Version : unleaded valve seat coversion
When cutting out the old brass seats, whats the OD for interferance fit on unleaded valve seats that measure 1.990" ?
03-26-2007, 04:55 AM
Why cut out the original seats? They are probably the best no-lead seats that you can have. And, if refaced properly, will last a long, long time. If yours are in bad shape, send them to Don Sullivan (Head Hog, Inc) and let him re-pour yours to original specs. He can provide the nitrited guides and valves for it, also.
Carl N. Olsen
03-26-2007, 08:00 AM
I like .006 -.007 interference fit on aluminum heads and .004-.005 on cast iron. Why would anyone want a welded up bronze seat? The whole idea of unleaded seats is for hardness not soft bronze. I have done hundreds of unleaded seats throughout the years and have no problem with cutting an accurate counterbore with adjustable tooling, freezing the seat to make it shrink and using Fluid Weld for lubrication and heat tranfer. Use cast iron valve guides and nitride coated valves and you will have a successful conversion. It is not rocket science, just good machining and paying attention to the details.
The seats are in very bad shape. I already talked to Don and was told it would be three to four months before I'd get my heads back. I can replace them myself for less than $100.00. I'm just not sure how much smaller the hole should be than my replacement seat OD. Thanks anyway. I'm sure the overlay is the better fix. It's just a time and money issue.
Thanks Carl. That's what I need to know. I really appreciate the info and coming from you I know the info is good. THe heads you rebuilt for me back in '01 are still running great. I'm doing most of my own machine work now or I would have sent them to you for the seat replacement. Hope everything is going good in South Dakota.
03-26-2007, 03:12 PM
I guess that I must have said something to offend you, Carl. I read back over my post and could find nothing that I considered strong. My point, and I should have gone on to say it then, was that the previous leaded fuel provided a cushion for the valves when they landed on the seat. Bronze does the exact same thing. Provides a cushion. The modern solution is hard valves and seats. I still like the bronze, for the cushion. And, if the builder/rebuilder is light with his cutter, only the smallest amount is shaved from the seat, to freshen it up. I've seen these refaced seats last longer than a set of rings would. In the old shops around here, a valve seat refacing or lapping went along with a ring replacement. That is my practice, also. Anyway, I'll try to clarify my answers better, before posting.
Carl N. Olsen
03-26-2007, 07:41 PM
I was not offended by your post and did not mean anything negative by it. You state that the bronze seats have a cushion effect on the valve, but that same effect will widen the seat in time thus providing more surface area on the seat and the valve face. When this happens there is more chance of a piece of cabon bonding to one or the other surfaces and creating a leaky valve seat. I have torn down numerous Panheads with the bronze seats that have been run a long time and all of them have had a wide seat on both the valve and head and have had signs of valve leakage. On the other hand I have torn down motors with hardened seats and found them to be narrower and more defined. In my opinion, there is no comparision between bronze and hardend seats and you are wasting your time and money going back to bronze. I like to upgrade the motors I build to modern specifications using the technology we have at our disposal to make them better than when they were new.
03-26-2007, 07:53 PM
I sure don't think pressing seats into Panheads is a good idea either. I have inspected many Panhead and cast iron Flathead valve seats that I and my friends have put many, many thousands of miles on and they hold up just fine! A factory Panhead (of Flathead) seat will last a LONG ,LONG time, and hold up to unleaded fuel just fine and will NEVER COME LOOSE!! Not that they can't be made to stay in, but the factory seats, and probably the welded to seats work VERY well in the real world of hard miles.
I'm sure the quality of the repair is dependant more on the experience and skill of the machinest doing the repair than the choice of poured-in seats or pressed in seats. I had a pressed in come loose right after a valve job was done, may have spun loose, who knows. But there are many done that way. My question is how do you support the area around the seat when pressing in a seat with .006 interference, or will freezing the seat shrink it down that much? Mike
03-27-2007, 08:47 PM
I'll vote for bronze, if for no other reason than installation of inserts into early Pans is risky. Later Pans have marginally more meat under the intake seat, yet it is still painfully common to find them where the port has cracked from the installation.
(Early ones can crack all the way to the nipple!)
Many of us have successfully installed hardened seats, including myself many times. But a poured seat (or even a bronze insert) hedges the bet against the extreme interference, as well as the probability of them falling out if combustion temperatures elevate due to advanced timing, vacuum leak, low octane fuel, etc.
(Those are the reasons for the extreme press fit.)
And with all due respect to Carl's observations, it must be noted that lotsa Pans had valvejobs hacked into them back when a wide seat was the typical industrial arts class norm. Widespread hardened seats in Pans is a relatively modern innovation of the late 70's on, when narrow seats became common dogma.
The beating out of seats has other variables like spring pressure, guide clearance, etc.
Since so many propane engines were spec'd to have bronze, I hesitate to dismiss it as too soft. They also have the advantage of less distortion from excessive heat.
There are very real reasons why the Factory went to the trouble to cast-in bronze seats instead of pressing in stellites. When Chubbles came along, the port relocation not only allowed more support, but more heat sink. Like the rest of the Chubble design it was a cost-cutting approach.
But we know even Chubbles could occasionally drop a seat!
If a hardened seat gives a 20% better life (I'm being generous), then that means a valvejob at 25,000 miles instead of 20,000 miles.
Frankly, that's not enough benefit to justify the risk, considering you are going to need to de-carbon anyway.
In my humble opinion, bronze seats contributed enormously to the legendary durability of Pans.
(PS: We are having a friendly discussion here.)
03-28-2007, 04:54 AM
Whats a "Chubble"
03-28-2007, 06:08 AM
Chubbles are what we call Shovels here, just south of Chicawgo.
Back in the days when I was wrenching under a tree and using a milk crate for a lift, I had a '80 Chubble/Shovel spit a valve seat out. I pinged the bore up with a punch, slapped some J B Weld on the seat and shoved it back in the hole with a little help from my 16 oz persuader. I hit it with some lapping compound and rode it for a year before doing a valve job while attending MMI. I rode it another two years before selling it and I would bet it still has the same seat in it now. So I'm not too worried about the seats coming out with a .006 - .007 interference fit. Cracks are possible but these old heads already have a couple of problems I'm going to have to repair. Any way the reason I tooled up was so I wouldn't have to farm out work and this is something I can do in house. I agree with Carl when it comes to upgrading with todays technology. With a three angle cut I can control my contact areas location and width. Cotton, you've probably forgotten more about these old Pans than I'll ever know but my '54 and '65 both have hardened seats and soon my '57 will too. I may know less about these old machines than any of you guys but that's my opine and I sure have enjoyed the debate.
04-02-2007, 08:04 PM
I have to agree with cotton. I have seen FLH pan heads crack with .006 interference on intake ports.The latter FL pan heads may hold up better because there not ported out like FLH pan heads but I still would not take the chance. I think the bronze hold up better than the seats they use in these new heads. The pan heads cast aluminum material gets worse with age and use because the high temp and hardens with age witch makes them brittle and prone for cracking.Your heads may not crack or drop a seat right away but I think murphy's law aplies here.
Once the hardened seats have been installed there is no going back to bronze, correct? Mike
04-02-2007, 09:46 PM
I believe Harley davidson sold bronze replacement seats back in the day. I also seen them in v-twin catalog.Some one like olddude.com or n.o.s parts.com might have them or you could make them. You don't need as much interference with the bronze because they have the same or close to the same expansion rate.
Im not sure what interference I woud use but it would be less stress on the head for sure.Don't forget to swage the seats in, this will give a little more insurance on keeping them in place.
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