Head rebuild “Ah-Sh*t” moments - exhaust valve seals and tappet guide hold downs

XK-Engine
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When I had my XK120 head rebuilt last month I didn’t know better than to NOT have oil seals installed on the exhaust valves. The new bronze exhaust valve guides came with the requisite grooves in them and the supplier lists the seals for the XK head as “12 required for 6 cylinder”, so that’s what I went with.

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Only later I came across this post from Dick Maury

and had one of them “ah, shit” moments.

Then, found this post from Roger King

and had another “ah shit” moment piled onto the first.

Both, of course, after having reinstalled the head and taken the car out on an extended shake down run.

So, I figured I’d tackle both jobs at the same time. I ordered four hold down kits from SNGB (excellently made, btw) and did up my E-type head while it’s still on the bench so was confident I could do the XK’s in situ without getting swarf in the engine.

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But I fretted about removing the XK’s exhaust valve seals while avoiding dropping a valve into a cylinder and turning the air blue in my shop yet again. I know from plenty of experience that learning from your mistakes is indelible, but learning from your successes is a lot better.

The course of action settled on was to put the engine at #6 TDC and attempt to free up the valve keepers and springs of #1 and #6 using compressed air with this little adapter I fabbed after smashing the insulation out of an old sparkplug:

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figuring if the keepers were already stuck onto the valve stems the raised pistons would keep the valves from dropping down. But after only 31 or so miles of running the keepers freed up without drama and I was able to do the other four without turning the engine. Well, sort of …

Couple of things. When I plugged in the air hose (at 125 psi) atop #2 the crank snapped clockwise to the bottom of the stroke, so I belatedly put the car in gear and applied the hand brake, so I had to re-establish #6 TDC before putting the cams back in - weren’t we just discussing learning from your mistakes?

The other thing is I consulted the All-Knowing YouTube for advice and came across a how-to video with over 2,000 hits - I won’t post the link because ime it’s a good example of what not to do. The fellow does the job with the camshafts installed, reasoning (at 4:20, if you decide to find it anyway) that any aluminum swarf that gets into the engine is “very, very soft” and won’t do any damage. Yeah. Right. He then drills the holes freehand

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and then taps them using the electric drill.

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and if you look closely at the result you can’t help but be left unimpressed:

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Eeeyew.
Why do people do a job like that, and then post on a public forum? Embarrassing…
It is perfectly possible to drill the holes freehand, and if very careful with swarf - carefully placed cleaning cloths etc. - do it with the head in situ, but tapping with an electric drill is crazy. It should be possible to fit these nice and even, with the flanges holding the guides safe and level.
I only fitted seals to the inlet valves, Nick, on the advice of Rob Beere. I bought the necessary parts from him, too.
I was advised that I didn’t need to fit the hold-downs on the inlet side, so didn’t, with consequent damage when two guides lifted and were comprehensively smashed. This episode has its own thread, as you have found - with theories and possible reasons abounding. But why not fit them anyway, to avoid any risk of being proved right/wrong?
I would just get the piston to TDC, then the valve shouldn’t be able to move far enough to leave its valve guide. I do use a compressed air line to hold the valve up on the V8s to allow valve spring swaps after running in, but I’m not convinced it’s really necessary.

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Goes to ability and experience, I suppose. I knew I couldn’t pull it off. I made a hardwood guide to keep the bit square as I drilled the holes. When I tried to make the guide drilling freehand it came out wonky, so remade it on the drill press … if I can’t drill even one hole straight and true freehand, how would I do drilling 24? :sunglasses:

But, yeah. The hold down kits are very cheap insurance. I’ll sleep better at night.

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…but useful, as it shows you many things to avoid

when creating Al swarf, heavy grease captures a lot, and everything should be covered with cloth (very important if creating steel swarf within several feet of magnetic alternator or starter motor)

A long thin tube taped to a vacuum cleaner will go down plug holes

I once tapped and helicoiled a spark plug hole with head in situ, used a borescope to check no swarf was in the cylinder

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I haven’t done it, but seems to me installing a spark plug helicoil in situ can be done carefully and confidently as you describe it, Tony. Grease on the drill bit and tap then vacuum with a tube in the cylinder for cleanup, after probing with a magnet to extract the broken tang. No risk. The worst sin this young fellow in the YouTube video committed (aside from assuming aluminum swarf is very, very soft etc.) is tapping the holes using a drill. These are blind 1/2” deep holes. I believe best practice is to begin to cut the female threads with a starting tap and finish with a bottoming tap, cutting and reversing a quarter turn at a time. You see the wonky screw angles and imagine chewed up female threads and can’t help but question the integrity of the fix, even with loctite. Some of the older kits use self tapping screws, I would not feel comfortable with either being an acceptable maintenance standard.

The more you dive into the voluminous J-L archive the more you come to appreciate how little things can mess up an engine rebuild. A piece of broken big end nut split pin finding its way into the oil pump. Bits of gasket sealant or some grit getting into the main and big end bearings oil passages. Installing a Rolon lower chain tensioner or a faulty aftermarket chain damper. Stem seals on the exhaust side. A fellow local J-Ler’s freshly rebuilt 4.2 engine suffered a catastrophic main bearing failure that broke the crank. It was a piece of camshaft sprocket circlip that got ground up by the timing gear and got into the oil pump.

Shit happens :sunglasses:

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Gday Nick,

Another trick I learned yeas ago to stop the valves dropping when replacing valve stem seals, in a non Jag, was with the piston at TDC fill the combustion chamber through the plug hole with a length of cord and of course remove it when done.

If you had enough cord you wouldn’t need to rotate the crank either.

It saves mucking around with adaptors and compressed air.

Cheers,
Jeff.

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The itty bitty oil pump drive can do that against the inertia of the engine?

A little swarf is unlikely to cause damage but that’s not a nice job, makes me feel much better about my first attempt… I broke the tap and used a self tapper in a blind hole next to it. This produced far less swarf, more like small granules, and was unlike to break off. But it’s so easy to remove the camshaft and do it right.

Compressed air on a piston has a lot of power!

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No more likely the rubbish blocked the oil feed to the main bearing.

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Does anybody still use slotted nuts and split pins on bearing caps?

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Nope!!

Gave that practice up 60 years ago (family business).

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That’s what I hoped! When I stripped my engine there were bits of split pin everywhere. I wondered if that was what caused the bore damage, but I’m not sure they’d find their way up there so it was probably a failed ring.

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I found split pin chunks embedded in the rotors of a 3.8L oil pump once. Not good.

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Ditto, more than once, and the bits came from “proper” factory split pins.

Chevy rod nuts RULE!!

:laughing:

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It absolutely can: if careful, any small bits of aluminum swarf in the cylinder will quickly be blown out.

One of the worst ‘ah shite’ moments I ever committed: buttoning up the last of the cooling tin on a Bug engine, then noticing the oil slinger ring, left on the bench.

The good news? I NEVER made that mistake a second time. :confounded:

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Mine was probably spending a day trying to work out why I was only getting 10psi oil pressure @2000rpm on a very expensively just-rebuilt 289 Hipo engine: engine out to get to the oil pump before noticing the valley rear oil gallery plug sitting on the bench.

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Well, if we’re comparing scars here … probably my most memorable ah shit moment was a few years ago just after mating the gearbox/bell housing to the refreshed engine, dropping it onto the frame, bolted down the mounts and attached the driveshaft. Next day whilst tidying up the shop I found the little can of oil in which I’d placed the new pilot bushing, still there.

Engine out, gearbox/bellhousing off, remove clutch etc.

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Nick, I like your use of a drill guide. The same process works for a tapping guide. For those that do not want to make their own, the use of drill / tapping blocks are standard for aircraft work. Kinda hard to take a fuselage to a machine so everything is hand drilled. So easy to make your own though.

To the “soft” aluminum swarf. Yes the aluminum is soft but it’s oxide layer is not. Aluminum oxide is one of the hardest substances around and each one of those pieces of aluminum debris is completely coated with it. Of course you don’t want any foreign matter in the motor, but even worse that you try to justify that foreign matter is easily digestible.

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Yes, that was the cause, apparently. No lubrication, spun main bearing. Still, an XK crankshaft is pretty massive and strong. It must be rare that one should break.

Back in the day the 200 tradesmen I worked with in my maintenance manager job taught me a few things about how important it is doing jobs the right way. They each had their own priority. Electrical was safety. Machinists and Instrument Mechanics precision. Welders art. Millwrights alignment, cleanliness, lubrication and vibration. Everything focused on longevity and function. All you gotta do is do is work to all of them.

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This will end up being a very loooong thread…:slightly_frowning_face:

Another Vee Dubb oopsie I did, but not as far a teardown to fix, was just buttoning up the pistons and jugs, then spotting the other half of the center main bearing, a-sittin’ on the bench.

Never did THAT again.

More will bubble to the surface, I’m sure…:frowning:

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Not justifying it: saying that small bits will not be an issue. That’s based on long experience.