Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties Valve seats

Valve seats

Moderators: Curt!, Pa

Post Sat Nov 29, 2008 10:53 pm

Posts: 903
Location: Hill City, Ks. USA

I looked at several sets of 80" jugs a friend has today. The seats are badly rusted and IMO too far gone to be ground. What is the best course of action? New seats?, spray welding and resurface?, They all have lots of meat left in the bores, there is surely a good way to fix these up.

Post Sun Nov 30, 2008 3:11 am

Posts: 1610
I usually reclaim valve seats on JAP engines using screw-in inserts, and it works well on ohv BSA engines as well. It isn't usual on British flatheads because (a) few people think they are worth the trouble, they convert to ohv instead and (2) the flat-shelf design, rather than the inset H-D style, makes it a difficult fix; but I don't see why it wouldn't work with H-Ds.

it may be that this is one of those good ol' Brit habits ( like sleeved cylinders ) that aren't usual across the pond, of course.
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Sun Nov 30, 2008 8:49 am

In my experience, seats come out. Yes, many methods have been used but the problem is that the seat is very large and the opposite sides of the seat are at very different temperatures (which doesn't happen in an OHV), and distort when hot. One side is released - guess what happens.
I haven't seen threaded inserts used, they may work (they were used as access covers in some early engines).
Most can be restored to useful condition by one or more of 3 methods:
1. larger valve head
2. change the seat angle to 55°, which removes metal without expanding the OD (but reduces low-lift flow) - requires a larger valve to start
3. cut the seat down as far as needed, and relieve the seat

Post Sun Nov 30, 2008 9:59 am

Posts: 3011
Location: Central Illinois, USA
Panic wrote:
"..the opposite sides of the seat are at very different temperatures (which doesn't happen in an OHV), and distort when hot. One side is released - guess what happens."

You mean it "shouldn't happen", but it can, especially when Pans have hardened seats crushed into the intake. There isn't enough matrix casting left beneath them to draw away heat in the event of advanced timing, vacuum leak, etc. Even Shovel seats suffer, as evidenced by the point of most distortion of a seat that has seen extended duty is nearly always over the port.

Yet another heat transfer problem can exist with a threaded seat, as there is no way to get absolute contact of the two threads, although a conductive potting compound such as "Seal-Lock" can help.

The way to keep a seat insert in place (beyond "clinching",etc.) is to pick a seat material of a similar thermal expansion coefficient as the casting.

Cast iron seats used to be common.
Now even bronze inserts are extinct.
Only "tool steel" seats (Martite, etc.) are readily available, requiring extreme press-fits to stay tight in the bore for heat transfer. And their metallurgy make them the most sensitive to temperature spikes, collapsing with disastrous results.

Last edited by Cotten on Wed Dec 03, 2008 5:10 am, edited 1 time in total.

Post Sun Nov 30, 2008 1:45 pm

Under ideal conditions, the insert should have enough "bulk" (cross-sectional area) to keep the temperature stable rather than let the side closest to the exhaust get several hundred degrees hotter, but there isn't room enough to be practical. The existing (new) seat is 1.97" IIRC; I'd like to see a 2.25" OD by .500" deep seat used but I suspect the intake seat would either crack to the bore, between seats or to a bolt hole.
I suspect that interrupting the fins (simple cut-off wheel) that connect the intake and exhaust port OD on the right side may help but keeping the exhaust side hotter (as is common in many other SV cylinders), but haven't tried it.

Post Sun Nov 30, 2008 7:12 pm

Posts: 693
Location: somerset, oh usa
I spoke with a guy that does big $ resto's of KR's. He says that he has routinely done his own repairs when necessary by preheating to 400 degrees F in an oven. He then repairs / rebuilds seats by brazing with a high nickle rod for cast iron and then slowly cools it by burying in kitty litter or similar. Remachine when cool.
Obviously there are less options with racers.

Post Mon Dec 01, 2008 7:06 am

Posts: 90
Location: Norway
I used universal valve inserts from w&W cycles. This has worked out exellent for many years of service (on the road, not in garage). A friend of mine did the machining of both the insets and the cylinders.

Post Mon Dec 01, 2008 12:57 pm

Posts: 903
Location: Hill City, Ks. USA

Thanks guys for the information. I realize the answer to my question is not a simple "Do this" . I understand more about the solution, now. I think the seats in question are beyond recutting the seat to 50 degrees or a bigger valve head. I am leaning toward a compatable tool steel or, if possible, a cast iron seat. If using a tool steel seat what would you recommend as being a correct press fit? I would think that this situation would lend itself to spray welding. Do any of you guys have any experience with this method? Is it even able to be done with cast iron?

Post Mon Dec 01, 2008 1:27 pm

Posts: 636
Location: Wisconsin, USA
Spray welding would work great. The trouble is it's not commonly used in the motorcycle world. After having a factory rep demo in my shop a few years ago, I decided to purchase one. The one I was after was discontinued, so I bought a very slightly used one on e-Bay. A nice unit with the exception being the valve that controls the flow of powder. It uses a thumb controled lever that pinches a hose under the hopper. The hose has decided to stay pinched on my torch, having been left shut for a year, so I can't get any flow. The hose is inaccessible under the hopper with everything being silver soldered together. The manual from the manufacturer recommended it be returned to them for repair. I just haven't had time to fool with it. Check with a major auto engine reman shop in your area and they should be able to put you in touch with a repair facility.

Post Mon Dec 01, 2008 2:18 pm
Pa Site Admin

Posts: 5552
Location: Ohio USA

I don't trust spray welds. They will chip off. Problem with tool steels is machining. You have to start with a non tempered tool steel or you can't cut it. Then you have to leave just enough stock for finish grinding to specs. The tempering process will distort your machined piece. This is why you need to leave grinding stock. There are many grades of tool steel. Off the top of my head, I can think of a few. D-2, H-11, and H-13. Pa

Post Mon Dec 01, 2008 7:14 pm

Posts: 604
Location: Largo, Fl

I agree with 37ULH...why not just build up the seat area with the nickle rod or even just cast rod and re-machine?

Post Tue Dec 02, 2008 2:31 am

Posts: 1610
I've seen this done and it certainly works
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Mon Dec 08, 2008 2:48 am

Posts: 14
Location: Daly City CA U.S.A.
The first set of UL barrels I had to work with had lowered or sunken seats , I took them to a machine shop and they set me up with 2" Hercules valves with sloted valve keepers, so a valve with a larger head is an option if you can still machine a seat in the barrel. Also If you have an automotive machine shop, see if they have any engine parts catologs with sizing charts for valves & valve gudies in them and you may find the larger head valve from a modern engine..

Later on I used some valve springs meant for a GMC in line six cylinder diesel, valve springs that were stronger than stock springs that I got from a machine shop that was repairing these 50's GMC bus engines that were shiped up to Frisco from LA on flatcars...

That nikle-bronze welding sounds good, especially if you can machine it...I never have seen any pressed seats in HD flathead barrels, that don't mean it can't be done....

Tom (08)

Post Tue Dec 09, 2008 7:57 pm

Posts: 693
Location: somerset, oh usa
It cannot be any harder material than the no lead seats that are routinely cut. I've run into some stuff that mechanical cutters refused to touch but stones are necessary for a proper finish anyway.

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