Re: maximum wear for 356 valve stems?

Posted by Owen_Dyneto On 2011/12/3 10:45:16

I was a bit hasty in my earlier response, on the way out the door. Stem to guide clearance for your engine is given at 0.004 to 0.005 for exhausts, 0.002 - 0.003 for intakes. I believe the stem diameters are given in the specifications which you can find on this site, so you could measure them if you wish and compare to spec. BUT, the wear on the stem will not likely be uniform as Blackbeerd has stated. Often you'll find a "step" at the top which does not go around all the way - if you can even begin to feel it with your fingernail, time to discard the valve. Also the guides, especially the exhausts, will likely be worn in a bell-shape at one or both ends, thus making any clearance measurements meaningless. You could use a bore gauge to measure the guide wear but chances are if there is ANY wear on the stem, the guide is worn beyond it's serviceable life and if left intact, even with new valves, will result in seat battering.

Installing new guides is not what I'd call a pleasant task but does not require removal of the cam and lifters. If however they are already out you can drive the guides down and out thru the lifter bores. If the cam is still in place, you can remove the hydraulic tappet assembly, drive the guide down part way and then break it off with a sharp rap with a chisel - simplier than it sounds - and then the remainder of the guide out from above in the same manner. Don't forget to check the height of the top of the guide from the block - on some engines the position of the intake guide is different from the exhaust guide. Although it's occasionally necessary to ream the guides for proper clearance, I've found it the vast majority of cases that it's not necessary. Only reface the valve seats in the block AFTER the installation of new guides.

Also, it's VERY important when installing new valves and grinding or even lapping the seats to measure and correct if necessary (by grinding from the stem end) the stem-to-tappet clearance - well covered in the shop manual and if you need to borrow the tappet gauge block, let me know.