Finally I have collected the refurbished Cylinder Head from my 1964 Mk2 3.4. Work done included new exhaust valves, guides and seats, new cam followers and a reground cam. The regrind was required as the case hardening had worn through on cylinders 1 & 2 (exhaust side) and some minor damage to the inlet cam. In total approx. 0.012in was taken off the cam…so the base circle reduction, resulted in an extra clearance of about 0.006in. New valve clearances have been set and done with standard shims. No welding required, which surprised the workshop as this is one of their specialty services. The head only required a very light skim to restore flatness.
Question-1: When rebuilding previous 1960 MG engines (including cam followers & new cam) at first start up the engine has to be run at 2,000 / 2,500 RPM for 15 or 20 minutes, I have forgotten exact figures. Is it advisable / recommended to do the same or similar with the XK engine?
Question-2 Should the carbon be removed from pistons (engine is in the car)…this is easy with the old cam in the sump engines as the engine can be rotated. I am concerned that removing carbon deposits from pistons down in the cylinder that some of the removed carbon will remain between cylinder walls and rings. There is not a lot of carbon deposits and two of the cylinders are clean as water was entering the cylinders and burning off the deposits. What is the best approach, do nothing or try and remove some of the deposits?
Is this a completely rebuilt engine, or just the cylinder head? If just the cylinder head, then I would recommend use something like Iskenderuan’s RevLube on it, start it and run it up to about 1500 RPM for just a couple of minutes, 4-5 maybe.
If carbon buildup is pretty excessive on the pistons, yes: if it’s a 16th of an inch or less, don’t bother.
That is the conundrum: I take care of that in the first five minutes of engine break-in: I choose for the rings in that period, and I make sure that I use heavy and copious amounts of molydisulfide grease on the cam lobes, if it’s a new cam.
The 10 minute or so run in at more or less fixed RPM was in the MG factory manual and is still done according to MG engine rebuilders…maybe it is peculiar to OHV engines. I recall a Ytube video from the Jag factory during the early / mid 60’s and the engines were bench “run in”, not sure for how long. Back in the mid 60’s I was lucky to visit a car assembly factory as a high school kid, and remember vehicles being driven off the assembly line onto what is now referred to as a rolling road, then driven at constant revs for about 5 minutes.
Back to the Mk2 engine, only the cylinder head has been refurbished, including cam. I plan to smother the lobes in molly, ensure plenty of oil around the valves, run the engine for about 5 mins then shut down, cool overnight and re-torque the head.