Shovelhead Head Question

[sswaney]

Here’s a straight up machining question.
What is the recommended interference fit on a valve seat insert?
The head pictured made 5000 miles before dropping the insert.
I’m measuring the fit at .0035. Obviously, that wasn’t enough.
I’ve heard .005” is a minimum. Thoughts and opinions?
Thanks in advance
20240907_100029.jpg 20240907_100051.jpg

[duffeycycles]

.0075" is a number many have used.Many STD panheads had seats drop,but not all.

[BigLakeBob]

I agree with Roger, it also depends on the material the seat is made from and its expansion rate as compared to the aluminum.

[T. Cotten]

Here’s a straight up machining question.
What is the recommended interference fit on a valve seat insert?
The head pictured made 5000 miles before dropping the insert.
I’m measuring the fit at .0035. Obviously, that wasn’t enough.
I’ve heard .005” is a minimum. Thoughts and opinions?
Thanks in advance

Its never straight-up, Scott!

I've had a head split like a gun shot from too much press:
seatcrak2.jpg

Hardened seats shrink when they reach a critical temperature (usually spiked by a vacuum leak), so your forensic measurement may not be its original diameter; Did it go out-of-round?

Its been decades,..
But with hardened steel inserts, I aimed for five and a half to six, but also used a conductive compound to avoid the natural insulation of a gap (Seal-Lock Fluid-Weld®), and then used my K.O. Lee 'clinching' tool.

My tooling is for sale as a lot. With substantial inventory too.

....Cotten

[dukekleman]

Swaney,

Interference should be anywhere from 0.006" - 0.008" on aluminum heads.
The Larger the O.D of the valve seat, the greater the interference required.
Be careful not to overheat the casting, you can permanently ruin the head and then all valve seats will fall out regardless of the interference fit.

Hope this helps,
Duke Kleman

[T. Cotten]

...Be careful not to overheat the casting, you can permanently ruin the head and then all valve seats will fall out regardless of the interference fit...

Is the aluminum casting ruined, Duke,...

Or did all the hardened seats shrink?

(That's why welding a bead upon them removes them so easily,)

Thanks in advance,

...Cotten

PS: While we are on the subject,
Hearsay was that early Shovels had "hard" seats, and then when they went to fat guides and seals, the seats got "soft".

My impression from cutting and grinding Shovel seats, the seats got "soft" early in the Seventies. That's subjective at best.

Can anyone shine light on the changes in Shovel seats and guides, etc?
Even though I did them for a living, they were too common to record.

Another Thanks in advance,. .. . .. . . . .. . . . .. . ... ..

[dukekleman]

Cotton,

The head is actually ruined if heated at to high of temperature.

It removes the heat treat of that particular aluminum alloy making it annealed, soft...then it's "holding power" is gone and the valve seats will constantly fall out.

Welding heads must be done very carefully or they will fail in typical service by the operator.

Hope this helps,
Duke Kleman

[T. Cotten]

I 'spose if the fins droop, Duke,...

You're probably right.

....Cotten

[dukekleman]

Cotton,

The temperature the cylinder head can handle depends upon the alloy used during casting...
As a rule, I'd advise you stay under 350F. Above that, proceed with great caution.

Duke Kleman

[T. Cotten]

Cotton,

The temperature the cylinder head can handle depends upon the alloy used during casting...
As a rule, I'd advise you stay under 350F. Above that, proceed with great caution.

Duke Kleman

But ain't that pretty much running temp for an OHV, Duke?

(Even PEEK plastic "can be used continuously to 480°F"!)

Flatty case temps were pretty close:

HEATCHRT.jpg

Why didn't the cases spit their races and bushings?
How did the aluminum heads hold torque at 500°F?

Thanks in advance,

....Cotten

[sswaney]

Thanks for everyones thoughts.
Yes Tom, for what its worth, the insert measures concentric.
This is a friend motorcycle.The heads in question are from V-Twin.The bike was being ridden daily while on a long distance road trip.
Averaging 300 miles a day in some hot weather this past summer. as I mentioned it had done 5000 miles since a motor rebuild.
Stopped for gas and when it was restarted it bent the rear cylinder intake pushrod. I initially thought the pushrod had worked loose and got up on the tappet
Assuming the insert hasn't shrunk as Tom suggests, the lack of of interference was the culprit.I guess

[T. Cotten]

Usually, Scott,..

They go out-of-round if it was heat-shrinkage, focused right at the exhaust port.

But with Tedd heads, all bets are off, including their choice of alloy.

....Cotten

[dukekleman]

But ain't that pretty much running temp for an OHV, Duke?

(Even PEEK plastic "can be used continuously to 480°F"!)

Flatty case temps were pretty close:

HEATCHRT.jpg

Why didn't the cases spit their races and bushings?
How did the aluminum heads hold torque at 500°F?

Thanks in advance,

....Cotten

Cotton,

Yes, most heads, at certain locations within the head itself, run around 250-350 Fahrenheit. This is why I stated you should not exceed that temperature.

I'm making a statement on a forum, you are open to various abilities and tooling at the hands of the readers globally. It would be very easy for someone to use a Rose Bud torch to heat the head and end up over heating it. This in turn ruins the heat treat in the cylinder head as I stated. If ranges of 500-600 degrees Fahrenheit are seen, heat treat loss can occur.
So in closing, 350 F is plenty hot for this procedure if you choose to heat the cylinder head that is made of aluminum alloy.

Keep in mind, cast iron cylinders (L Head/ Flat Head that you provided an image of) that house the valve seat itself, are much different in many ways of conversation.

Aluminum alloy heads, to this day on current production vehicles, continue to have occasionally valve issues. This conversation does not stop at antique motorcycles nor at motorcycles in general. There are many auto manufacturers that deal with this also.

I'm trying to keep the post topic short in material because there is a lot to cover regarding this particular area...

Bottom line, choose your valve seat material for it's application and location within the head. Be sure to have precise rigid tooling for cutting, get your interference fit machined properly, do not over heat the head and ruin it should you choose to heat it..., perform a correct and concentric valve job on the seat, tune the engine properly (Ignition timing, AFR, motor oil quality, plug heat range, etc ) and hope the customer avoids riding situations that can overheat things. This is about all you can control. After that scenario's arise and a valve seat may possibly fall out. But keep in mind all the areas to Dot I's and cross T's mentioned above. Failure to follow through them is a gamble at best.

Hope this helps,
Duke Kleman

[T. Cotten]

I was addressing the aluminum, Duke!

Not the flatty valve seats, which we know are not even inserts.

....Cotten

PS: Late edit...
Face it Folks,
If even four hundred was a limit, there wouldn't have been a golden age of American motorcycling.

Tedd's modern alloy may be even better, but their quality control issues mean we may never know.

PPS:
Forgive me for another late edit everybody,..

But let us please cut to the chase,
The heat that shrinks a hardened seat, main race, or any other insert didn't come from the aluminum casting, it came from nasty combustion or friction.

Although the insert may be ruined, aluminum castings serve their purpose of distributing the heat and saving themselves awesomely..

(That's the spellcheck spelling of a word that doesn't need to exist.)