I recently bought a supposedly ‘ready to install’ Series 3 XJ6 head from a J@ck@ss in CT I found on ebay. Stupidly I bought it outside ebay so no recoure. Well long story short, the head is very far from how it was described. The issue I’m most concerned with is this:
Instead of using the correctly sized cam-follower adjusting pads to get the clearance right after cutting the valve seats, this guy just ground all the valve stems so he could re-use what was in there. The funny thing is that he still failed miserably at getting the clearances between .012 and .014 – they are all WAY off.
My question is what do you think about using these valves now? I know that grinding valve stems was an excepted practice but I thought there was some kind of hardening on them that would be removed when ground? Thoughts?
Well, here’s what I found on my rebuild. Clearances were all over the place, mostly tight. Two stem tips had been ground. Upon disassembly, found about half of the exhaust valve seats had been ground too deeply, valves were recessed into the seat.
Grinding the stem tips is acceptable on some modern OHC engines, but ours should not be ground, as there is not a lot of thickness between the stem end and the keeper groove.
Old_ed - Good point about the distance between the end of the stem and the keeper groove. I need to look at them all very closely and see just what he took off.
Lovell - the valves and seats have actually been ground and lapped (45 Degree seat not 3 angle) so they’re good to go. I’d just need to adjust them properly
Nigelplug - I don’t think the seats were cut too deeply - he just ground the stems to avoid buying the correct shims. It was probably not much but I will measure them all to be sure.
So lets say that everything is okay with the seats and the amount he ground off the stems was not enough to affect the keeper… in that case is there any reason there would be an issue with this? Is there any sort of hardening on the stem that could’ve been disturbed? I’ve never heard of Jag valves having anything like that.
Does anyone know definitively if a hardening process was applied?
No problem grinding the stems. Critical for the stem tip to sit proudly of the recess in the retainer, and the shim to hit the stem. New valves need to be fitted to the engine, not the other way around.
I measured all the valves very carefully today and he’s taken an average of about .016 off the valve stems. There is still a good amount of meat above the keeper. The wear area of the stems show -.001" . Luckily, although I don’t like what he’s done with it, the head itself seems to be in very good shape.
Money is an issue with this build because I’m already way over budget for this project… so I still need to think about what I’m gonna do as far as valve replacement.
its possible to fit undersize shims down to .070", but its a hassle, not recommended, and the shims are about $10 each anyway ( i did this once, due to the same issue you have)
Yup, I agree completely Tony - I wouldn’t mess with making undersize shims. I should’ve mentioned in my original post that although the clearances were all over the place, they weren’t outside of the normal shim range to correct. As long as the little bit he took off the top of the stems doesn’t weaken that area - and I don’t think .016ish really does - I will probably use them.
when a fellow sold me “fully rebuilt” head that must have been done by a goriila with an angle grinder, it was such a mess that another head was really needed. Instead, went and spoke to a pro Jag engine guy, and he gave me some undersize shims.
He advised me that shaved stems should be ok, that undersize shims are ok, so long as there is tappet/spring keeper clearance at all times, dont go under .070, or risk shim shatter, that engine ran for along time, but is now out to investigate (pre-existing) high oil consumption
If you can rock the shim in situ before you install the tappet, it proves that the shim is not sitting against the spring collar and is therefore ‘safe’ provided it’s not super thin.
If the stems are good as described, the fitter may have refaced the valve and then ground an equivalent amount off the stem to keep in range.
The fact that he did a sloppy set of clearances could just be that he was a cheapskate, not a gorilla. If money is tight and you double-check everything, the components may be perfectly usable, just not optimal. If in doubt throw ‘em out, but it’s not essential to toss them if you know what you’re doing.
for me the issue with grinding the valve stems is the achieved ‘flatness’. its possible that they are not flat and that you get different clearances depending on where the stem is situated.
New valves would be my preference.
The machine that refaces the valves at 45 degrees (occasionally 30) also swings the valve around to present the stem tip perpendicular as it travels across the stone (or vice versa).
Doing what should be precision machining freehand, is asking for trouble, I agree. I don’t know about Jaguar, but firms like BSA (who owned Daimler before Jaguar did) had their own foundry. Often their metallurgy was superior to aftermarket parts, even branded ones. You were therefore sometimes better off refurbishing, say, a BSA exhaust valve than putting a new one in and trusting the unknown quality.
Phil - I was worried about that as well. They ‘look’ flat and if they were done in a valve stem grinder that’s designed to do it you’d think they’d be good. I don’t have the specialty machinists tools to check but I found an old-school local machine shop and took the head over there today. One of the other things the guy that sold me the head did to me is fail to provide a scratch-free mating surface. This machine shop is gonna take care of that and take a look at how the stems were ground… I’ll get the verdict next week.
Peter - He only removed around .016 so they don’t contact the spring collar - that’s one consolation The more I go through it and measure everything the more it seems like the valves are perfectly usable.
Buying new valves wouldn’t be a huge expense but if the seats need to be cut again to lap them I may be opening up another can of worms resulting in having to grind the new valve stems to make them fit again anyway… or worse, having to replace the seats which I totally cannot afford at this point. It’s a conundrum alright.
I very respect the superior knowledge on these forums so now understand more about valve stem grinding. My comment was based on some recent posts where using a V block with a bench grinder was suggested. I have also seen this practice used in professional workshops. Hence my comment
The more I go through it and measure everything the more it seems like the valves are perfectly usable.