Ok I have been working on my motor for the bronco & in cleaning up the heads & such. well being the clean freak i am i decided to spray some carb cleaner down the intake ports. on the 6 that the valves were closed 5 of them held the liquid 1 did not. after more thinking i sprayed some penetrating oil in there put the spark plug back in & turned by hand & it blew bubbles so I thought burned valve for shure so I pulled the head & they look fine? Then sprayed oil in to all of them to see how the others did & they all leaked when laying there. Is some leakage normal or do these heade need work?
John

 

its common for slight seepage,but, if they have any miles on them,like 50k plus,I would take the in,it will run much smother when done. The 351M and 400 are hard on valves.also,make sue the pushrods are ok,as in the ball ends get worn . how it helps,Scott

 

Cool thanks supposed to have around 30000 on the Ford Factory rebuild. Can still easily see the crosshatching on the .030 0ver bore cylinders so I am going to go for it.
Thanks Again
John

 

might need to do a quick lapping compound job. the possible potential problem is your guide is worn and allowing your valve to float around in different position. Cause of guide wear is possible rocker arm issue not pushing down on the valve straight. So to test this is have head on engine assembled with head gskt torqued. Get a black marker and mark all your valve tips and then install your rocker arms/pushrods. then roll engine over by hand. Once you do this pull rocker arms off and inspect you wear pattern on valve tip. this will tell the story on your rocker arm alignment. If not centered in middle of valve tip you have a issue. could be pushrod length or something else in valvetrain. Have to look at all componets and figure something out. Possible caused are milled heads or decked block and running factory pushrods. If you mill or deck block you need to change pushrods also. If a lot of material has been removed. .040 you will begin to notice the wear pattern changing. Good luck and let me know what you found. curious??

 

I agree with the lapping with compound job, as long as your valves are not recessed in the head already and the valve stays dedicated to the seat lapped. Stock length pushrods are 9.480-9.500 inch, I would measure them to see if the factory rebuild changed this length, and do the alignment test as described after head re-assembly.hope this helps.

 

I know the exhaust valve guide are prone to wear. I just get my aussie head done and all exhaust vale guide had to be replace. My block was deck and heads shave for clean-up to straight them. Had problem with pushrods. Had to buy pushrod lenght adjuster and a black marker to fix my geometrie. The wear patern have to be in the center off the valve tip, otherwise valve guide wear a lot faster.

The machinist where a got my head done check them by pulling the valve with one hand and the other finger on the top off the guide. It make a suction but the better way is to mesure the wiggles or distance when the valve tip is even withe guide. Divide this mesure by 3 to get the aproximate stem-to-guide clearance.

Maximum steam to guide clearance is 0.005 inch. New steam to guide clearance range is 0.0010-0.0027 inch for the intakes and 0.0010-0.0030 inch for exhausts.