leaking intake valves compression loss. Pictures added.

[fastback 427]

The 12 to 1 390 in my fairlane started running like crap last year. Popping through the Carb and running rich. Chalked it up to Carb and parked it. Yesterday we started diagnosing. Started with compression test. Cylinders 5,7,8 were 235 to 240 psi. They rest were 190 to 210,  low for that engine, as it was 245 to 250 new. So we hooked up air to the chambers and the low psi chambers leaked like a seive into the intake. So three hours later the engine is sitting in the run stand with the heads off. Lotta crud on the valves for a two year old engine. Only thing is the intake gasket looked a little saturated and may have been weeping. I'm going to disassemble heads clean them up and lap the valves in by hand and check the guides and look for bent valves. The heads are ported dove f-5 aluminum, stainless race valves, viton seals. Anyone seen this before? Possible causes? Anything to look for?

[Joe-JDC]

Fuel leak from carb power valve would wash down the intake manifold ports and the head would be clean where the fuel was rich enough to coat the back of the head of the valves.  IF there is oil caking up the valves coming from the intake gasket, then there would have been blue smoke while the engine was running and a loss of oil from the pan, and the dipstick would have let you see the drop in oil.  If it is guides, then the intake manifold and intake port of the heads will be clean, but the back of that valve will have caked buildup on it.  My question is were there hardened seats installed?  The seats may have been improperly installed and moving around.  Let us know what you find.  Joe-JDC

[fastback 427]

Thanks for the advice joe-jdc. I'm taking them apart today. The motor never puffed blue but smoked black when under full throttle. Also the intake runners are dirty, maybe oily. I'll try to post some pics. Hardened seats were installed.

[machoneman]

Before you take the heads apart, bench them and add some solvent or charcoal lighter fluid to the intake ports to detect leakage past the seats.   

[cammerfe]

Your Dove F-5 heads likely have valve pockets somewhat different from what's usually seen. Dove calls them 'ice-cream-scoop' style. This unique shape creates a different short-side turn radius and it also makes it easy, when porting, to remove too much material under the seat inserts.

The comment above, from Joe, regarding looking for some loose seats should be paid particular attention to!

KS

[fastback 427]

Thanks again guys. I will definitely try some solvent behind the valves! Cammer, you are right about the short side radius. I did a mild port and didn't have to remove much around the seat. I'll check the seats really good.

[fastback 427]

I sprayed some Carb cleaner on the back of the valves and it ran right out. Cleaned the chamber and removed an intake valve and you can see carbon build up on the seat. So far the seats themselves look fine but only have a couple done. I think lapping them in will be OK but still need to find the cause of the crud. The valves and seat area look perfect.

[fastback 427]

pic of the head as it came off.

[fastback 427]

Intake runner.

[fastback 427]

pic of the start of cleanup. First port job so dont be to hard on me.

[machoneman]

If you must port (and don't have Joe D. Craine looking over your shoulder) follow the S-A generic guide:

http://www.pirate4x4.com/tech/billavista/PDFs/Head%20Porting%20DIY%20by%20Standard%20Abrasives.pdf

[fastback 427]

Cool link, thanks machoneman! I did these three years ago before I knew about Joe d. Craine   Just cleaned up the chamber, relieved the valves, gasket matched and sent them to someone with a flow bench for the final touch up. Got some good numbers for me but I'm sure nothing like the master Joe d. 

[cammerfe]

Due to the unique layout of the F-5 head, Dove has made available some drawings that show what needs to be removed in order to get max flow.

I used a set of F-5 aluminium heads for a magazine project I did some years ago. Wayne Kuchtyn did the work and we ultimately flowed them on the Superflow 1020 at Livernois. I've moved since that time and my copy of the information is in a box somewhere in my storage but the original diagrams and information from which we worked must be still available from Dove.

KS