Packard Forum Index » Post-War (1946-54)

1947 356: What's the minimum valve stem diameter before I have to discard the valve?

If the stem is worn enough to even raise the question, then certainly the guide which is MUCH softer has worn considerably more and will almost certainly have to be replaced.

Wear won't be even along the whole length. If you measure some wear or worse, see it, you need new valves.

G'day 9 mains,
to PackardInfo.

Sorry can't help regarding the valve stems, but invite you to include your '47 in the Packard Owner's Registry.

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.

Thanks very much, Owen! I really appreciate your advice. I'll probably end up replacing most of the guides.

Owen, I have a question. Are the guides really easy to drive out? What does the driver look like? What does the valve stem height block look like and what are its dimensions.I was told by a guy that it is too hard on the block driving them out and also that it is easy to brake the new ones trying to drive them in. My guy wants to ream out the existing guides and install bronze bushings. Believe he means the oil impregnated bronze. Then grind the seats and replace at least all the exhaust valves. I know about the valve stem height and also the fact that the valve guide height is different between the intake and exhaust.

Reaming or boring the existing guides for a bronze bushing may be an acceptable procedure, though I don't know anyone who's done this type of engine that way. It is routinely done on engines that don't have a guide per se, like the V8s. Certainly getting the new bore perfectly on centerline of an old, worn guide sounds challenging.

I've driven out gobs of valve guides, probably not as many as Ross, but lot of them. Some come out easier than others. I use a KD valve guide drift which has been discussed on these pages before - I forget the number but no matter, it's NLA. But easy enough to make from ordinary steel by anyone with a suitable lathe. Leave a pilot pin to just fit into the guide, perhaps 2 inches long, then a larger diameter section to comfortably rest on the top of the guide but be slightly smaller so it can fit thru the guide hole, and then a larger diameter top section of diameter and length to suit.

I've driven in gobs of guides, never broke one and no reason why they should brake. Pack them in dry ice for a few minutes and they go in much easier, though that's certainly not necessary.

I don't off hand know the dimensions of the valve gauge, but when you get to that point you can either borrow it or I can make some measurement. People have said it's the same length as the hydraulic portion of the tappet with the spring removed but I think I'd want to verify that first if I was going that way.

Note that bronze guides have a different tolerance the iron guides. The material expands more and if you ream it to the same size as iron, your valve will stick when the engine gets hot.

9 Mains, some years ago I had a '39 Cadillac 60 Special with the valve-in-block 346 V-8 that needed new exhaust valves and a new valve guide. I purchased a set of stainless steel valves and a new guide from Egge. I was nervous about replacing the valve guide as I had heard similar stories about all the bad things that could happen with this job from the Cadillac community as has been discussed here. I decided to go ahead and do the job and hope for the best. I had a drift made by a machine shop, as O_D described, and proceeded to pound out the guide. I struck it with low force and it came out easily and cleanly, and the new one went in the same way. I measured the end of guide to block distance of the other exhaust valve guides, and drove in the new guide to that measurement. As described by O_D, the valve replacement job on the Packard engine has one more step than I had to do with the Cadillac; in that you need to drive out the guide part way, break it off, and finish driving out the remainder of the guide. The Cadillac engine had enough room to drive the guide out in one piece. You should do just fine with this job and I encourage you to do it. Good luck, and let us know how thing go.

(o[]o)