Intake seat movement , lost seal. SBC

[vwchuck]

This happens a lot on air-cooled stuff as our heads run at 400+ degrees. If you run them hard you will find the seats moved on you. We just re-cut and keep running them. With your stuff you probably got that combustion chamber hot somehow. Detonation, pre-ignition and air bubble?

[joespanova]

This happens a lot on air-cooled stuff as our heads run at 400+ degrees. If you run them hard you will find the seats moved on you. We just re-cut and keep running them. With your stuff you probably got that combustion chamber hot somehow. Detonation, pre-ignition and air bubble?

Good points , but I have zero recollection of heat being an issue............non the less , anything's possible.
I guess I should have mentioned , the ONLY change in this engine has been going from a 4.040 bore to a 4.155 bore and an increase of 1 full point in compression ( basically 13.2ish to a 14.2ish comp ratio). Not doubt the tuning "window" has gotten smaller apparently.
Fuels have been C-12 and Sunoco Supreme. Timing around 38-39 degrees.

[randy331]

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 .

I know of one with similar results as jon. Guy had one that leaked between the seat and head and it ate out some aluminum to the point you could tell it at an idle. Car was running 6.00s 1/8 mile, and he thought it'd get in the 5s with that fixed. It didn't run any faster. I think at rpm there just isn't enough time for a lot to leak out.

Randy

[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 .

I know of one with similar results as jon. Guy had one that leaked between the seat and head and it ate out some aluminum to the point you could tell it at an idle. Car was running 6.00s 1/8 mile, and he thought it'd get in the 5s with that fixed. It didn't run any faster. I think at rpm there just isn't enough time for a lot to leak out.

Randy

I can see that.....BUT , on 3 seats dropping down 60-70lbs all at the same time??

[joespanova]

what about compression blow back up into the t-ram on 3 holes at high speeds....... what' s that going to do to mixture throughout the plenum?

[WeingartnerRacing]

On a set of profilers I ported I built a 383 dynod it it made good power. Took it home did some routine checking and 4 cylinders would loose 50% in leak down. Tore off heads sure I broke something. Nope, did vacuum test and I wouldn’t pull vacuum, it did before. I recut the valve job, put them back on the motor, and redynod the motor. I just knew it would pick up a ton. It gained 19hp that’s it. Rechecked everything and all was good. Just something to chew on.

[joespanova]

On a set of profilers I ported I built a 383 dynod it it made good power. Took it home did some routine checking and 4 cylinders would loose 50% in leak down. Tore off heads sure I broke something. Nope, did vacuum test and I wouldn’t pull vacuum, it did before. I recut the valve job, put them back on the motor, and redynod the motor. I just knew it would pick up a ton. It gained 19hp that’s it. Rechecked everything and all was good. Just something to chew on.

Yeah , I'm chew'n and I don't like the taste..........now I'm expecting very little in return.

[WeingartnerRacing]

Sorry man maybe you will see more Nothing is proven until tested. When you think about it though very little time in the combustion process for air to leak out, maybe a thousandths of second. How much could get out?

[Carnut1]

On a set of profilers I ported I built a 383 dynod it it made good power. Took it home did some routine checking and 4 cylinders would loose 50% in leak down. Tore off heads sure I broke something. Nope, did vacuum test and I wouldn’t pull vacuum, it did before. I recut the valve job, put them back on the motor, and redynod the motor. I just knew it would pick up a ton. It gained 19hp that’s it. Rechecked everything and all was good. Just something to chew on.

Yeah , I'm chew'n and I don't like the taste..........now I'm expecting very little in return.

Joe, have the seats cut with a 50 or 55 degree seats. They need to be done anyway. Lots of pros swear by the higher angle seats. Might be a nice kick.

[maxracesoftware]

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 .

[b]You can see the seat moved because it created a small "finger nail" catch of a ledge just above the seat[/b] , the seat had been pushed into the counter bore .

How many Runs do you have since my last Valve Job on your Heads ?
is that still my Valve Job , or did you do another when you went to 4.155 Bore

that was going to be my very 1st question-> is there a sharp edge lip between bottom of seat insert and aluminum ??
.... so thats a Yes from your previous post i just read

usually means possible valve float pounding seat inserts
aluminum heat treat going soft
valve guides looser ..rocking seating action on seat insert pounding seat more on one side causing edge lip
....combinations of 3 above together

i can't exactly remember your Track 1 surface or if i angle milled or straight cut or even milled them for you at that time ???

are they milled all the way into intake seat inserts top angle ??

have you spun Valves in Valve Grinder to see if all still concentric ?

are all valves "free" up and down movement in guides ???
very free movement up and down..but still good snug clearance in guides
or some binding in mid portion of travel inside guide ?

PS: i just re-read ... noticed Lip was above the seat insert .... but same sort of problems happening
look for Lip edge at bottom of seat inserts too ... more on one side than the other

[jsgarage]

Joe, my experience with seats moving even a little is, the next move is completely out of the head. You get to exercise the welder, clean out the pan & replace a piston or two. I would replace the seat(s).

[joespanova]

OK , thanks guys for your help.
Larry , no valve jobs since you had them. I dont run the car that often so if I'm in the engine I usually just disassemble heads , check for anything weird, usually lap the valves just to see if everythings ok. Always it is , til now. The guides check about .002 or so clearance ( maybe .0025 ) using small hole gauges and mic'ing the valve @ .341.
Last year I broke second gear and hit the high side @ 8900 or so BUT I 've run the car way past that ( meaning I've run it probably 10-15 runs after that ) and IIRC even had the heads apart..............MAYBE.
I say maybe because I'm gettin' old and CRS , LOL
I don't think you actually did a valve job , did you? IIRC just flow and port texture......I 'd have to look.
I dropped the heads off to have 3 seats cleaned up. That's it , that's all I'm going to do now.
You told me you are done with porting?

[maxracesoftware]

OK , thanks guys for your help.
Larry , no valve jobs since you had them. I dont run the car that often so if I'm in the engine I usually just disassemble heads , check for anything weird, usually lap the valves just to see if everythings ok. Always it is , til now. The guides check about .002 or so clearance ( maybe .0025 ) using small hole gauges and mic'ing the valve @ .341.
Last year I broke second gear and hit the high side @ 8900 or so BUT I 've run the car way past that and IIRC even had the heads apart..............MAYBE.
I say maybe because I'm gettin' old and CRS , LOL
I don't think you actually did a valve job , did you? IIRC just flow and port texture......I 'd have to look.
I dropped the heads off to have 3 seats cleaned up. That's it , that's all I'm going to do now.
You told me you are done with porting?

this is Invoice/Flow Sheet i have = January 16 , 2014

Lite Valve Job + Lap Valves ( meaning touchup seats with Stones type Valve Job )

no milling on Heads

just new Porting + Flow testing

if you have any sharp-edged Lip at bottom of seat inserts between aluminum
....recommend complete new seat inserts ... go oversize + possibly interlocking + deeper /thicker inserts
....otherwise, its possible to drop a seat insert ... engine will be history !

even no Lip ... still have someone study situation carefully + think about new seat inserts + do it is recommended

[joespanova]

OK Larry ,
thanks for the "heads up"........or is it "heads down" , or is it heads up , thumbs down , or........