Sorry to revisit this again, but I’d appreciate an engineer’s opinion here.
Unable to sleep comfortably I thought I’d recheck the shim engagement in the valve caps before refitting the head on my 140’s 3.4 engine, whilst everything’s on the bench and easy to work on. So I removed the inlet cam again, and checked the depth of shoulder retaining the shim.
All valves are installed properly with all new parts. The machine shop, very experienced in XK engines, supplied the valves (make unknown to me) and fitted new valve seats. The collets and caps are the more modern short type to allow stem seals, supplied by Rob Beere Racing. Each valve stem has had a few taps with a heavy hammer with a soft brass drift to help seat the collets.
The photo shows the most critical shim space. This shim has just 0.0035" pocket to sit in, and will have a valve clearance of 0.004". The sums tell me that when the cam is on the back of this lobe, there will be a gap of 0.0005" which could theoretically allow the shim to pop up and slip sideways.
I have dummy-assembled the old, worn parts as a comparison, compressed in a vice to simulate spring pressure. The same dimension on all these is generally around 0.009", perfectly safe (second photo - although one is 0.005").
Sorry to ‘bang on’ about this, but this is the original C-type block and head and I would be very upset if it got wrecked by a slipped shim. Do I have a problem here, or is this within limits and I’m worrying about nothing? I haven’t checked the exhaust side yet, where the clearance is even greater at 0.006"…
Further investigation might have revealed the culprit here.
I have tried dry assembly of various combinations of parts new and old, and taken as many measurements as I can effectively. This isn’t easy as the groove in the valve stem is hard to measure effectively with hand verniers etc., and the taper of the valve cap and collets is also hard to measure accurately.
But the telltale is the depth of the collets inside the cap. As far as I can tell, valve length and height above the spring seat is the same for new and old, and the collet groove looks to be correct. But I have found that the distance from the top of the assembled collet to the top face of the valve cap is significantly greater using an old cap than it is with a new one, all other parts being new. Therefore I suspect that the valve cap taper for the collet fit has been machined slightly differently, causing the cap to sit slightly lower on the valve stem, which leaves the tip of the stem closer to the cap height, hence the reduced retention of the shim.
Photos attached - the greater dimension is with the old cap, the lesser with the new. Not the most scientific means of measuring but I’m pretty sure it’s correct.
So - try different caps? I can try another supplier, or re-use my old ones, if I can get the rust off them. I’d need to stick them in the lathe to reduce height as I’m now using stem seals. Or would it be safe to risk the reduced retention heights? All opinions gratefully received!
I have been monitoring this thread since you initiated it and the shim retention pocket depth has give me pause and I am glad you revisited it, as I was about to comment on it today. My engine builder had a similar issue when he rebuilt my B head that I used on my 120 block back in 2015. He found that the new valve stem keepers that I had supplied would not fit properly and subsequently used the original ones, which fit perfectly. The pocket that the shims fit into is around a 1/6", as Rob had mentioned in prior responses. This is what I would expect.
The Jaguar Repair Manual states that the valve ends can be shortened up tp .005" if needed, which is really almost negligible, but a step in the right direction, potentially doubling you current depth of .0035". Common sense may allow more stem shortening if you look at how far the stem protrudes above the spring retainer.
I think more conversation with Rob Beere about their parts may be in order, since they rebuild and support serious racing engines, and should well know what to do. What you have is just not right IMHO.
And you are building your engine for actual use in today’s world, so you need to get it right.
Thought I would just throw this out there: IIRC, there are 7 degree keepers(collets) and 10 degree keepers. A 10 degree pair of keepers, mated with a 7 degree retainer, would probably prevent the retainer from rising as high on the valve stem…just a thought.
I bought a single valve cap from SNGB to check, and it’s identical to the RBR one. No prizes for guessing where they come from, then…
I don’t understand why the original valve caps, used with all other new parts, give a much better location of the shim than the new valve caps.
Using a new valve cap, one of my exhaust valve shims sits down into the recess by only 3thou. As the clearance gap for that valve is set at 6thou, that gives it a 3thou gap to slide sideways when on the back of the cam. If I assemble that same valve with the same new collets but using an old valve cap, the shim sits down into the gap by 10thou, giving plenty of side location.
I would just use the old valve caps if I weren’t fitting stem seals. Maybe better off using the safe caps and junking the seals?
Hi Roger…i would get this problem posted on the XK engine section of this forum for a wider audience. …so far no one here has had a similar problem…but most if us see it as an issue…there are some forum members that im sure would give good advice but i havent seen them contribute yet…maybee they havent seen it in this XK section…Also consider posting on the UK E type forum…there is a lot of experties there that dont use Jag Lovers…Steve
Thanks for the tip Steve, I know you’ve followed the E-type posting as you’ve posted in reply!
I think I’m making some progress on this. To try to get the bottom of the problem I ordered a single valve collar from Moss Europe, purely on the basis that in their photo their version is a different colour.
It arrived today, and is clearly of a different manufacture from the SNGBarratt offering (which Beere’s also supplied). It is short, the same length as the SNGB one, but does not have the tapered end the others all seem to have (but the longer original did not have).
Here’s a photo of it assembled with the new valve and new collets:
I’ve replied on the E-type forum, but just to summarise:
I had a very productive chat today with Peter, who is very helpful and is already on top of this problem.
The issue is indeed the taper in the new valve collars, which has not quite been machined deep enough into the collar. This is surprisingly difficult to measure, but they are making a tapered depth gauge to check current and future stock. Peter is going to keep me informed on progress. I’m impressed with the way they are taking this seriously and giving it priority. I have had recent issues with a completely different UK supplier for Triumph parts, regarding new reproduction wheel studs fracturing at around 30ftlbs torque - they just weren’t interested, so it’s very refreshing to see Barratt’s taking this seriously and acting quickly.
Hi Roger…as far as im concerned SNGB are at the top of their game regarding customer service…the owner Julian Barratt is a member on the UK forum and will jump in if an issue is flagged to him…I try to forward any potential issues to SNGB so they can get on top of it…Steve
Brief update: the valve collars (spring retainers) from Moss finally arrived and are now fitted. I have at least 20thou of shim engaged with all the retainers, so no danger of anything moving. Now, at long last, the head can go back on.
It could have been an expensive one, too. The last time I took the tappets off after setting the gaps, two of the shims had indeed slipped down inside the tappets just with turning the cam on the bench.
I’d suggest a simple check of the height difference between the top of the collar and the valve stem should be routine during a head rebuild, just need a short straight edge and a feeler gauge, at least while there may be rogue collars still out there.
So in conclusion you purchased new valve spring retainers from Moss Europe that had a proper shim pocket depth and allowed you to install valve stem seals on your intake valves only. Moss lists the retainers for use on intake and exhaust.
I am in the middle of a rebuild of a 3.8 L motor (which uses the same retainers) for one of my MK 9’s and this information is very timely. I am a bit surprised that others have not experienced this problem and commented. However, it’s not the first time I’ve heard vendors just slough it off and say you’re the first one to have a problem. On my last rebuild I bought tappets from XK’s and they were undersized right out of the box, and half of the ones I got from SNG were out of round. I was told I was the first one to have an issue.
That’s the part number I used for the collars from Moss Europe. They are now out of stock in the UK, I believe. I used these for all 12 valves, with stem seals on the inlets only. They are not quite the same as Barratt’s, as they are not tapered at the base, but they are the same (short) length.
To be fair to Barratt’s, they did not pass this off as the first time they’d heard of it, they took it very seriously and are addressing the issue now. They were simply not aware of the issue as they had had no feedback from others. Peter said that they do batch test their parts at random, but as I found out the actual taper machining is much harder to measure than you’d think. They have now designed a tapered gauge so that this can be checked as well. It would be nice not to have had the problem in the first place, but I’m actually pretty impressed with the way they are dealing with it.
Brief update - had a chat with Rob Beere about this and he couldn’t have been more helpful. The caps are on their way back to him and he will sort things out. I am most impressed with his service, which has been excellent at all times. Both companies have taken this seriously and dealt with my problems very well - I shall have no reservations about using them again in the near future.