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Engine - General, Exhaust & Induction Topics about the general engine items, exhaust system discussed here & Improving the intake tract - air filter to intake valve.

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post #1 of 15 Old 09-07-2018, 08:50 AM Thread Starter
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Dropped Valve Seat

I have a ported big valve G head with a dropped valve seat. There is very little material left between seats so boring for an oversize seat would result in overlapping the intake/exhaust valve seats.

I came across this on Mini-Mopar:
Avoid "siamese" valve seats, where the intake and exhaust seats are touching. This design does not allow for proper heat expansion and the exhaust seat will transfer heat to the softer intake seat, and the shape of the seat can become distorted. The valve will not sit properly and low compression and severe valve wear can result.

I don't have a shop nearby that specializes in head repair. Actually, I didn't get a good vibe from the only local machine shop, either. So I'm hoping that the knowledgeable members here can help me out.

From my research, I have a few options:

1) Weld and re-bore - I'd have to find a good shop. One source I came across suggested that all seats and guides would need to be removed to preserve their interference fit due to the heat/expansion involved. I don't know if this is true.

2) Stake the seat - I don't like this idea. The seat had dropped before, was peened and eventually dropped again.

3) Overlap/Siamese the valve seats - See above but I don't know if this applies with these seats (why would they use different material?). I think this would be the easiest to have done, at least semi-locally. Unless...

4) Could I go with a taller (deeper bore) seat to restore the interference fit? From cross-cut pictures of the head it looks like there is room above the seat to work with but I don't know if taller seats are available.

Thanks in advance for any input.
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post #2 of 15 Old 09-07-2018, 10:08 AM
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Re: Dropped Valve Seat

if this is the second time the same seat has dropped I'd look for another head especially as a G head should not have this issue
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post #3 of 15 Old 09-07-2018, 10:15 AM Thread Starter
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Re: Dropped Valve Seat

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Originally Posted by Dr. Johny Dodge View Post
if this is the second time the same seat has dropped I'd look for another head especially as a G head should not have this issue
It's the second time but the repair job was crude. Even by lawnmower standards which is where peening is often done.

Also, it was beat on at the track. It's new life is that of a cruiser that only occasionally sees high revs.

I have other heads but the cost to bring them to this level is prohibitive. I will have it checked thoroughly prior to any repair.
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post #4 of 15 Old 09-07-2018, 10:23 AM
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Re: Dropped Valve Seat

I lathe my valve seats out of chrome moly . This way I can make them to any size so I get a good interference fit. Sometimes only a few thousands is needed for a good tight fit. No head boring is necessary.


Sinking valve seat changes the valve train geometry.
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post #5 of 15 Old 09-07-2018, 10:31 AM Thread Starter
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Re: Dropped Valve Seat

Quote:
Originally Posted by moparracer 35 View Post
I lathe my valve seats out of chrome moly . This way I can make them to any size so I get a good interference fit. Sometimes only a few thousands is needed for a good tight fit. No head boring is necessary.


Sinking valve seat changes the valve train geometry.
Is this something that most machine shops are capable of doing? Isn't it possible that the bore is out of round?

I'm not wanting to put a regular height seat deeper but rather install a taller seat that would sit deeper in the head. If that makes sense.
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post #6 of 15 Old 09-07-2018, 11:39 AM
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Re: Dropped Valve Seat

If bore is out of round it probably would be just a few thousands and could be made round without doing very little cutting. Then lathe a oversized seat to fit the head. Press fit is about .007 on aluminum head
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post #7 of 15 Old 09-07-2018, 08:43 PM Thread Starter
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Re: Dropped Valve Seat

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post #8 of 15 Old 09-07-2018, 09:04 PM
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Re: Dropped Valve Seat

nice bite outta the casting - and two cracks between the seats

second time for the same seat , same head I'd definately quit that head and move my parts to another one

where in ontario are you ?

I have a g head I don't need that has it's own problem ... NO CAM CAPS

if you can find a machine shop that can align hone a head - a challenge in it's self - then figure out the bearing that fits if modded - there IS one , then , if you wanna conquer the challenge of this head I have ... you can have it

's got no valves , been rough ported but not finished .. needs valves , springs and all that ..

clean G casting is about it . like I said with a challenge all it's own
got it and a FB head for free from some local shop that closed
-neither had the damned caps ..both were ported

I'm scarborough / pickering border area
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post #9 of 15 Old 09-07-2018, 09:12 PM Thread Starter
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Re: Dropped Valve Seat

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Originally Posted by Dr. Johny Dodge View Post
where in ontario are you ?

I have a g head I don't need that has it's own problem ... NO CAM CAPS

if you can find a machine shop that can align hone a head - a challenge in it's self - then figure out the bearing that fits if modded - there IS one , then , if you wanna conquer the challenge of this head I have ... you can have it

's got no valves , been rough ported but not finished .. needs valves , springs and all that ..

clean G casting is about it . like I said with a challenge all it's own

I'm scarborough / pickering border area
Thanks, Johnny. That is very generous. I'm far north of you and, as we both know, shipping is prohibitive up here. For close to what it would cost to ship I could buy a good G core on eBay with free shipping to the Michigan UP. Also, I doubt the local shop could fix it.

I'd really like to have this one repaired. It's a nice head.
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post #10 of 15 Old 09-07-2018, 09:20 PM
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Re: Dropped Valve Seat

LOL .. K
FREE two ported doorstops !!!
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post #11 of 15 Old 09-08-2018, 07:41 AM
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Re: Dropped Valve Seat

well you have two options
a weld in repair and grind down and machine. which will be 300=500$.

or grab a newer Ghead with out the reoccuring issues and either port it yourself
or pay someone to port it . 300-500$.


then have which ever head you choose rebuilt. 200-300$.

if it was MY money.. i would get a head with out peen marks. and with out seat issues.
and start from scratch. swap over your valve train after porting.

not seeing anything on that head that cant be replicated by a normal porter for 300-500 $. check into "jokerz performance" for some porting. they ported a 655 head of mine. came out amazing

I have acute Taurocoprophobia. Achew!
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post #12 of 15 Old 09-08-2018, 08:24 AM
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Re: Dropped Valve Seat

Quote:
Originally Posted by RyGuy View Post
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If you make a .002 oversized seat and install that only adds .001 on side next to other seat which is very very little.
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post #13 of 15 Old 09-08-2018, 09:33 AM Thread Starter
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Re: Dropped Valve Seat

Quote:
Originally Posted by masterjr3333 View Post
if it was MY money.. i would get a head with out peen marks. and with out seat issues.
and start from scratch. swap over your valve train after porting.

not seeing anything on that head that cant be replicated by a normal porter for 300-500 $. check into "jokerz performance" for some porting. they ported a 655 head of mine. came out amazing
Thanks. I'll check them out if I decide to go that route. I also have a nice 782 head without the normal cracks between seats to consider if I decide to start fresh.

Quote:
Originally Posted by moparracer 35 View Post
If you make a .002 oversized seat and install that only adds .001 on side next to other seat which is very very little.
This would definitely be the most efficient option. I'm concerned that the sliver of material between the seats may fall apart, though... There are two cracks (visible in the pic) and it looks as if the material is bulging into the empty bore from the other seat.

So, can anyone help answer these questions:

1) Weld and re-bore - I'd have to find a good shop. One source I came across suggested that all seats and guides would need to be removed to preserve their interference fit due to the heat/expansion involved. I don't know if this is true.

4) Could I go with a taller (deeper bore) seat to restore the interference fit? From cross-cut pictures of the head it looks like there is room above the seat to work with but I don't know if taller seats are available.
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post #14 of 15 Old 09-09-2018, 02:53 AM
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Re: Dropped Valve Seat

Dont believe the info on mini mopar about not using siamese valve seats, this is common in the diesel world, distortion of the seats is not an issue if the correct material seat is used. had my 655 head set up that way, my machinist does a LOT of work on high performance diesels and farm tractor engines that are beat on mercilessly for 8 months of the year.

Basically you just install hardened seats on both the intake and exhaust-you'll never have an issue.

i'll ask him when i see him later on this week what material seat he used on my head. I do know he has told me that in an aluminum head application you MUST use a non magnetic seat as they expand a lot less when heated so dropping a seat is not an issue.
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post #15 of 15 Old 09-09-2018, 09:13 AM Thread Starter
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Re: Dropped Valve Seat

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Originally Posted by ohnotagain View Post
Dont believe the info on mini mopar about not using siamese valve seats, this is common in the diesel world, distortion of the seats is not an issue if the correct material seat is used. had my 655 head set up that way, my machinist does a LOT of work on high performance diesels and farm tractor engines that are beat on mercilessly for 8 months of the year.

Basically you just install hardened seats on both the intake and exhaust-you'll never have an issue.

i'll ask him when i see him later on this week what material seat he used on my head. I do know he has told me that in an aluminum head application you MUST use a non magnetic seat as they expand a lot less when heated so dropping a seat is not an issue.
Thanks. Let me know what you find out. I'm assuming you haven't had any issues with your head. How many miles have you put on it?
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