Valve stem length (possible) issue

[Crammysauce!]

So, after getting my new motor back together, I had a good bit of drivetrain noise during the first few minutes of run-in. One of my rocker shafts broke in the first minute and a half, so the process was pretty much over for the time being. I figured I probably had the wrong length pushrods, so I ordered some new rocker shafts / rockers (needed them anyway) and a pushrod length checker. I came up with the exact same pushrod length as I had originally. I called Fullthrottle, and talked to one of their guys - he said it could be contact between the base of the valve spring retainer and the valve guide. I am running a .496 lift cam, so I figure this is quite possible. Anyone have any experience with having to cut down the valve guides? How much material am I looking at taking off? Thanks!

 

[turbofabricator]

This is a process that needs to be VERY precision. The stock exhaust valves do not have enough clearance for high lift cams. If you cut the stock exhaust guides down too far, then the "oil pump" cut into the stock valve will no longer work correctly, and you will pass alot of oil down the guides. The stock valve stems have a groove cut in them that is tapered at the top of the groove and has a sharp edge on the lower surface that pushes the oil out of the guide. ("oil pump") If you cut the guides down, then the groove will stay above the guide all the time, negating the process. If you slide an umbrella seal over the stem, it will not work either, because it will end up riding in the stem groove and will not seal. If you replace the valves with aftermarket stainless valves and use PC seals then you can cut the guides down as far as you like. You can also use TTA exhaust valves, too. They came from the factory with no oil control groove in them and they also have seals on them. If you remove a minimum amount of the guide material and leave .080" clearance, you might be OK. I would suggest replacing the exhaust valves with stainless steel versions and have the guides cut for PC seals.

 

[Crammysauce!]

I actually took care of the problem by taking off just a little material from all of the valve retainers. Worked great! Thanks for the response just the same - I'm sure someone else needs this info.

 

[bison]

I would replace all the rocker shaft bolts at this time with new ones to be safe.

 

[Crammysauce!]

I did. Trusting 20 year old bolts is not on the menu.