Importance of Valve Job

[BlackKnight]

Your saying it has a radius seat on the intake? It doesn't have sharp edges.

Does the intake seat look like the exhaust seat?

This is a sharp edge, both seats.

it looks nothing like that! the heads are out being fixed so i can't take a picture but they are nothing like your picture. your's look very professional and what i see in other race prepped heads.

[jsgarage]

Didn't I read a post here awhile back on aluminum heads not sealing well until they're hot and have been run a bit? My street engines are not out at the bleeding-edge of what's possible, so its never happened to me. And I've used aluminum heads both Ford & GM since the '80s.

[MadBill]

There are some 'flexi' castings that need a torque plate attached during the final valve job. I read of an extensively ported 2V hemi Alfa Romeo head that started leaking past the valves at 20 lb-ft. of torque on the head bolts...

[ProPower engines]

There are some 'flexi' castings that need a torque plate attached during the final valve job. I read of an extensively ported 2V hemi Alfa Romeo head that started leaking past the valves at 20 lb-ft. of torque on the head bolts...

Thats correct and there is quite a few more heads both foreign and domestic made as well as many aftermarket.

While the heads that are affected are mostly max ported heads I have seen some aftermarket Dodge heads benifit from a T/Plate valve job as well as other max ported iron heads.
While some customers don't mind the extra effort and it shows on the dyno when a leak down is done after break in but others will not accept the idea of the possibility of leaking valves after a head is ported and then bolted on a block.
It seems that some GM heads can benifit from this when the bolt colum in the center of the heads have been thinned out during porting. The newer heads produced these days are much better made by those that offer CNC port work compared to hand porting as they have made improvements to their castings to help prevent chamber distortion.

[Dodge Freak]

Good info! Use a torque plate for valve jobs, make sense but I never would had guessed it

[user-3597028]

I heat cycle new aluminum heads in the oven to 200 degrees and back to room temp several times before doing any seat/guide work to them.
I have found over the years that a brand new casting will move and shift around after its initial heat cycles. I would guess some of this is the press fit on the inserts themselves. The aluminum castings seem to take a set after heat cycling. It takes virtually no time to do this. In the oven, set timer and temp, repeat.

I had a new Canfield BBC set on an engine once that we dynoed for 10-12 pulls and then went back to do some more work in the ports. I checked the seat runout, and some of them were as much as .006" out. When I initially did them, they were all less than .001".

Keep in mind that anytime the seat runout exceeds the guide clearance, you have binding and head-to-stem flexing. I feel this is probably one of the leading causes of valve stem breakage.

I am a real seat runout nazi. I also touch off the seat angle with a fine stone on every one.

[BlackKnight]

how common is it to see "gaps of light" shinning around the valves after placing a mini flashlight into the port?

[wil8115]

how common is it to see "gaps of light" shinning around the valves after placing a mini flashlight into the port?

you should not see light at all.

[BlackKnight]

i didn't think so. i have had many sets of heads ported, bike and car heads), and i have never seen a set so bad. the heads flow good (clean to .900 @ 390/270 cfm) as is, but doesn't seal and as been stated, "without seal all is lost." what's the possibility of flow suffering with a proper valve job?

[mtkawboy]

FE Ford heads are extremely critical as far as using a torque plate for the valve job. Before using one the 2 end exhaust valves always leaked when bolted on the block

[MadBill]

...what's the possibility of flow suffering with a proper valve job?

More likely to improve. Any VJ that bad for sealing is likely to be bad for flow also. (But JIC, given above comments, maybe you should leak check it with a torque plate in place.)

[SWR]

Tightened the guide clearance to half the stock clearance on Porsche 944 turbo 2-valve heads to make the valve stop dancing about wearing out the guide and after it was sealed as never before when cold... and leaking like hell when warmed to 80ºC. Re-did the valve job at elevated temps, sealed well... and promptly got complaints that they leaked like hell when at the customers place (i.e. cold).

[BlackKnight]

...what's the possibility of flow suffering with a proper valve job?

More likely to improve. Any VJ that bad for sealing is likely to be bad for flow also. (But JIC, given above comments, maybe you should leak check it with a torque plate in place.)

thanks

[ProPower engines]

how common is it to see "gaps of light" shinning around the valves after placing a mini flashlight into the port?

Thats quite common with todays mass produce replacement aluminum heads.
I think it was hit on the head a correction by Cedarmachine for the problems of VJ's going bad after a run in is to preheat the heads a couple cycles while a t/plate is attached.
Lots of the OEMs have bad valve sealing issues and the guide clearance is always on the large side when the head is off and daylight can be seen between the seats.

But the iron heads that suffer this fate I bet is from production valve seat cutting methods.
They don't take the time to be sure they seal well. I had some eddy Vic Sr 440 heads a couple week back that if you put 100lbs springs on them they would not seal the seats and valves were so bad.
These had a max CNC port job done to them.
I think that fact that the valves are machined not ground have a lot to do with bad runout and I am not sure what they are using for a S+G machine but the seats were square with bad high spots between the seat inserts.

After the 1st set I had a few years ago I started using a T/Plate to do the V/J's on any high aluminum end heads when new.


CedarMachine

Did you bolt the head to a T/Plate for the heat cycles or just bake them 1st as is out of the box??
I am wondering if the heads would benifit from the clamping to get them fully relieved its kind of a catch 22 deal with the seats needing to face upwards to ba safe but the guides are the other way facing down.

[justahoby]

how common is it to see "gaps of light" shinning around the valves after placing a mini flashlight into the port?

Thats quite common with todays mass produce replacement aluminum heads.
I think it was hit on the head a correction by Cedarmachine for the problems of VJ's going bad after a run in is to preheat the heads a couple cycles while a t/plate is attached.
Lots of the OEMs have bad valve sealing issues and the guide clearance is always on the large side when the head is off and daylight can be seen between the seats.

But the iron heads that suffer this fate I bet is from production valve seat cutting methods.
They don't take the time to be sure they seal well. I had some eddy Vic Sr 440 heads a couple week back that if you put 100lbs springs on them they would not seal the seats and valves were so bad.
These had a max CNC port job done to them.
I think that fact that the valves are machined not ground have a lot to do with bad runout and I am not sure what they are using for a S+G machine but the seats were square with bad high spots between the seat inserts.

After the 1st set I had a few years ago I started using a T/Plate to do the V/J's on any high aluminum end heads when new.


CedarMachine

Did you bolt the head to a T/Plate for the heat cycles or just bake them 1st as is out of the box??
I am wondering if the heads would benifit from the clamping to get them fully relieved its kind of a catch 22 deal with the seats needing to face upwards to ba safe but the guides are the other way facing down.

COuple years back I recut my brand New RHS Iron heads because of this.... to the op...light is a no-no
Some people check with gas or kerosine, some with vacuum...
I like the tourque plate idea, I may steal that for my use