I had my XK120 head rebuilt this week by R&B Automotive, coordinates below. I supplied new valves, phosphor bronze valve guides, snap rings, stem seals and springs sourced from Welsh. @Robert_Laughton supplied the shorter valve spring seats, collars and keepers required for converting a pre-‘69 head to stem seals. The head was delivered to the shop assembled with the original valves but without camshafts, buckets and shims. Existing tappet shim numbers also provided for benchmarking.
The job included initial cleaning, removing and replacing the valve guides, reaming the intake guides, cleaning up the existing stellite valve seats, 30° flat grind on the intakes and 45° on the exhaust, 0.005” shave, six spark plug hole helicoils plus one additional helicoil for a stud hole in the front underside. The new exhaust valves were oversized so had to be turned down, but this gave the machinist more material to work with to compensate for recessing the seats. Final cleanup and reassembly.
Rob also leant me his formidable collection of ~300 tappet shims so I was able to achieve precise 0.004” and 0.006” clearances on the intake and exhaust sides. Shim thicknesses are a comfortable range from 0.092” to 0.102”. Two exhaust valves were topped, still allowing plenty of freeboard above the spring collars.
(I just have to share this pic of Rob’s communal (“take one, leave one”) shim collection. There’s even a bunch of oddball undersized and chamfered shims for excessively topped valve stems.)
I’ll get the head and the manifolds back on tomorrow. I was running rich before the teardown despite having the carb jets screwed most of the way up so I’ll need to figure out what’s going on there - likely the starting carb needs adjustment too.
Well, John, I failed to take a video of the first start - just as well because I had to shut her down after 10-15 seconds to address a coolant leak and an oil leak. However, just to make it up to you for not following through I took this video of the first shakedown cruise. In addition to the head rebuild I installed a set of Mahle pistons. I put 31 miles on it today to help bed in the rings.
Pleasant day here in Niagara, Canada, this 15th day of December, 2023. No salt on the roads, 9C and sunny, but I think this may be it for the old gal till spring. Likely a couple more runs in the E-type, though.
I think I’d drive it until the weather told me no, then put it up for the winter. Gives you a chance to identify any latent issues. Then you have the winter months to rectify them.
sometime next week
