Intake seat movement , lost seal. SBC

[joespanova]

I had these Brodix heads for years , SBC 23 degree track 1s. For some reason the intake seats on 3 holes have lost their concentricity. Read that they moved radially......... losing seal . You can actually see the carbon trail at the short turn. That's where the seal is lost. Same valves , springs aren't old either. Comp 944s IIRC. Steel 2.05 valve, RPM 8500 MAX.
I've used these heads with out ever having this issue for a long time. This is the first this has happened.
No piston to head contact either. Is it just age / fatigue?
And if the seats are re cut , whats to say it wont recur in short order?

[Carnut1]

I had these Brodix heads for years , SBC 23 degree track 1s. For some reason the intake seats on 3 holes have lost their concentricity. Read that they moved radially......... losing seal . You can actually see the carbon trail at the short turn. That's where the seal is lost. Same valves , springs aren't old either. Comp 944s IIRC. Steel 2.05 valve, RPM 8500 MAX.
I've used these heads with out ever having this issue for a long time. This is the first this has happened.
No piston to head contact either. Is it just age / fatigue?
And if the seats are re cut , whats to say it wont recur in short order?

Most likely this is due to guides going away. Service guides and recut seats and return to service. Thans, Charlie

[Carnut1]

Valves, seals and springs will also need attention.

[joespanova]

[quote=Carnut1 post_id=726961 time=1521996518 user_id=21334
Most likely this is due to guides going away. Service guides and recut seats and return to service. Thans, Charlie
[/quote]


The guides with an oiled / prelubed stem seem to be in pretty good shape ( read that you can't detect any radial movement )...but thats worth looking at.........suggest a clearance ? .0015-.002 intakes , .002-.0025 ex.?

[strokersix]

Do seats ever rotate in service? I don't know, just asking. If so, that could explain your observations.

[Carnut1]

[quote=Carnut1 post_id=726961 time=1521996518 user_id=21334
Most likely this is due to guides going away. Service guides and recut seats and return to service. Thans, Charlie

The guides with an oiled / prelubed stem seem to be in pretty good shape ( read that you can't detect any radial movement )...but thats worth looking at.........suggest a clearance ? .0015-.002 intakes , .002-.0025 ex.?
[/quote]

Depends on guide material. Most of my junk is iron with k-line thin wall guide liners. .0012 in and .0016 in has worked very well so far. As far as aluminum heads with heavy bronze guides I have not done enough of them to give advice.

[JonKaase]

The seats have been pushed into the aluminum. Usually the force of combustion plus a little detonation. the thinner wall seats do it worse- not much footing. If the seat had a big radius on the bottom it has less surface area and that makes it worse also. But at peak power it will usually flex the valve enough to seal it. I would bet when you fix it it will not make more power. It's unbelievable, but in the last 50 years of doing this, I have not had one time when we fixed leaky seats that resulted in making more power. But we still always fix them because it's not right! Kaase

[joespanova]

The seats have been pushed into the aluminum. Usually the force of combustion plus a little detonation. the thinner wall seats do it worse- not much footing. If the seat had a big radius on the bottom it has less surface area and that makes it worse also. But at peak power it will usually flex the valve enough to seal it. I would bet when you fix it it will not make more power. It's unbelievable, but in the last 50 years of doing this, I have not had one time when we fixed leaky seats that resulted in making more power. But we still always fix them because it's not right! Kaase

Jon , this is a bad leak....cranking pressure down from say 210-215ish to 150 on 3 holes. Connecting a leak down tester or just an air line , the blow by was HUGE on those 3 holes. If it was a small leak I'd be incline to agree , but this is bad. If it makes the same power I will have lost faith completely in my "intuition" ...

[ProPower engines]

[/quote]
Jon , this is a bad leak....cranking pressure down from say 210-215ish to 150 on 3 holes. Connecting a leak down tester or just an air line , the blow by was HUGE on those 3 holes. If it was a small leak I'd be incline to agree , but this is bad. If it makes the same power I will have lost faith completely in my "intuition" ...
[/quote]

If the heads have been done a few times it may also need some geometry attention.
It the guides wear inline with the rocker action in a short time it may be scrubbing the guide out causing the issue.
I am guessing the shaft rocker setup if used may need to relocated. If stud mounted then again they may need to be looked at. If the rockers are putting force into the stem causing it to rub the guide out it is had to find without a gauge to check it with at times a wiggle of the valve stem will not tell how bad they really are.

[KnightEngines]

It probably pinged a bit, maybe a bad batch of fuel, maybe you changed something & threw the tune out?
Either way, if the guides are good then you can probably touch up the seats with stones, get it back together & keep an eye on the tune.

[joespanova]

It probably pinged a bit, maybe a bad batch of fuel, maybe you changed something & threw the tune out?
Either way, if the guides are good then you can probably touch up the seats with stones, get it back together & keep an eye on the tune.

I hope that's the case.
Geometry wise , I gotta believe its pretty good. Its a stud mount setup.
Look at it this way , what is the likelihood of THREE intake seats going out at the same time , given the heads were apart not long ago and there has never been any evidence of concentricity issues.
Combine this suggestion ( above , Knight engines ) with what Jon states and there it is.

[JonKaase]

It would be interesting to dyno it before and after. Just pull the heads and fix the bad seats and reassenble. Leave it on the dyno. I have done this drill many times. I am 0/100's on this. The leak down and cranking compression doesn't have enough pressure to flex the valve closed. Usually a test like this looses about 5-10 HP because the bores were disturbed. Espically if it was together for a long time. Kaase

[rebelrouser]

Not an expert, but I have seen the seats move on a lot of aluminum heads, especially ones that have been ported. I blamed loss of material in head from porting, incorrect torque or not being careful in torqueing them, plus stress being relieved from maybe running a little hot, on SBC the two center exhaust port make a big hot spot in the head when running. I have always just touched them up and run them, never an short term issue. But over time same stress that caused it will most likely do it again. I see this in engines put together by my buddies a lot more than the ones I assemble, I just chalked it up to myself paying more attention to the torque sequence and checking my torque wrench for accuracy on a regular basis.

[joespanova]

It would be interesting to dyno it before and after. Just pull the heads and fix the bad seats and reassenble. Leave it on the dyno. I have done this drill many times. I am 0/100's on this. The leak down and cranking compression doesn't have enough pressure to flex the valve closed. Usually a test like this looses about 5-10 HP because the bores were disturbed. Espically if it was together for a long time. Kaase

I ran the car this Fri night at Reynolds. Just driving to tech and then stabbing the throttle some I knew something wasn't right.......and my "hunch" was right..............it was off .25 ( thats 2.5 tenths , lol ) in just the eighth. Hence the comp test reflecting the pressure loss. I know what you're saying though.........I'll bet flexing would NOT seal this , it was probably leaking 60-70%.
You can see the seat moved because it created a small "finger nail" catch of a ledge just above the seat , the seat had been pushed into the counter bore .

[mag2555]

Time to get a valve job done with a Head plate bolted on.