Pin vices and valve lapping

[Steamchick]

I have done the "hose" trick on car head refurbishment. But using the power tool to spin the valve while lapping tends to way overdo the lapping so a broad seat is achieved, not the narrow seat that is much better at sealing.
Poppet valve sealing is very complex - according to the doctor engineer I met from the company's research place.... A narrower seat has a higher contact pressure than a broad seat so will seal better. It will also run-in better, due to the higher pressure upon closing, when the hammering of the valve on the seat work hardens the contact face. Similarly, as the valve naturally rotates in small increments while the engine is running, the rotational surface rubbing and lapping is quicker with a narrow seat. Progressing the hand lapping of valves onto seats simply gives far better results than 1 quick blast with a powertool. Although experts (like race mechanics, et al.) do it with power tools, but have the experience to provide optimum pressure and contact time to develop the optimum seat lapping.
Enjoy,
K2

 

[Steamchick]

Longboy, I have similar problems as my smallest 3-jaw drill chuck only goes down to 0.5mm (0.020in) drills, and just fails to hold those. Using pin chucks in a larger 3-jaw I can hold smaller drills down to 0.35mm, but Concentric it becomes a problem.
The best solution I have is a regular drill chuck on 3mm dia shank drills that I buy in packs of 10 from 3b@y for a couple or 3 quid. I have 0.25mm, 0.30mm and a few larger sizes for drilling gas jets, and the 3mm shank carbide drills are never a problem like I used to get with regular fine twist drills.
K2

 

[Longboy]

Longboy, I have similar problems as my smallest 3-jaw drill chuck only goes down to 0.5mm (0.020in) drills, and just fails to hold those. Using pin chucks in a larger 3-jaw I can hold smaller drills down to 0.35mm, but Concentric it becomes a problem.
The best solution I have is a regular drill chuck on 3mm dia shank drills that I buy in packs of 10 from 3b@y for a couple or 3 quid. I have 0.25mm, 0.30mm and a few larger sizes for drilling gas jets, and the 3mm shank carbide drills are never a problem like I used to get with regular fine twist drills.
K2

Thanks Steam. Well I'm getting by drilling needle seats with a #50 drill in the half in. chucks. Sewing needles are for the lower numbered '50s drill sizes, but I can't find a packet of any given needle number. They come as a variety pack and only two sizes within I can use. The rest are throwaways. I'd like to use #2 safety pins...... but their shanks are a #60 drill diameter, hence my inquiry of chucking up pin vises with the tiny drills.

 

[Steamchick]

I can only say "suck it and see". My pin vices are certainly not as accurate as needed to hold a small drill Concentric when held in a larger chuck. Partly because the surface of the pin vices are all knurled,, for fingers to grip.... I have bought a total of 4 pin vices and decided 3mm shank drills work better than the pin vices.
K2

 

[Bentwings]

While working in a hot rod shop I also was transitioning to an R&D company they had a microscope capable of viewing cylinder heads . So I took a race head with both lapped and not lapped valves and seats clearly you could see the contact when seats and valves were bkued soni put the lapping stuff away for good if a valve leaked I just te ground or touched up seats we had a really good valve grinder so it was no trick to true up a valve The big thing was many builders simply had too much valve stem clearance I don’t remember the exact number but initially thought clearances were too tight but with proper seals I don’t think I ever had a galled up valve guide. I fixed a lot of them but most of ours wre bronzewall with hard chromed valve stems on the stainless valves the super exhaust valves had the same when titanium intakes came out we left clearances alone and again no problems unless the engine had done other issue like burned pistons Then seats got coated with burned aluminum but a simple touch up was all that was necessary . Of course if burned aluminum got sprayed on the valve stem then we just installed new bronze walls and reamed the bores.

 

[Bentwings]

I forgot to add I saw guys over sizing guide bores then re using valves that were tweaked thus not straight so they lapped furiously then wondered why the engine dropped a valve. Well flex any steel often enough and it will break at 9 grand rpm you get a lot of cycles very quickly. The early aluminum heads dropped valve seats regularly some tricky precision machining and carefull installation took care of it