4.2 Overhaul, appreciate thoughts, comments & suggestion

[kgb123]

I'm in the process of trying to restore my 68 2+2 back to original (or as original as possible) condition in time for its 50th birthday in 2018...3 years..a sinch

Block has been honed which has identified some strange ware in all of the pots. Option is to rebore to +40 (has previously been rebored to +30) or to have new liners fitted and take back to standard. I'm keeping the car so think new liners are the better option, any thoughts?

Crank. I had the plugs pulled and sludge and crap cleaned out. Main bearings part had previously been ground to +20 and was OK but BE bearings part had been poorly ground to +30. Initial check showed a slight taper when previously reground, but T&L have recovered to all round +30 so I'm thinking should also be OK, but have read some posts where suggestions were made that anything over +20 they would replace the crank. Again any thoughts

I have the opportunity whilst the crank is out to have it machined for rear oils seal conversion..Appreciate thoughts and comments on that option

Cylinder head appeared to just be a bit tired with signs of ware. Plan is to replace the valves and also have new un-leaded exhaust valve seats fitted. Loads of meat left on the head itself, so will be checked for tru and have pressure testing etc. Anything else I should be considering?

Crank will be balanced (once I get a new clutch assy) and all parts returned to me as I want to do as much of the rebuild as possible

Any comments suggestions welcome.

[christopher storey]

Several points :

1. there is a huge amount of meat on these cranks, so that 30 thou undersize is not something I would be worried by - and bearing in mind that a properly looked after engine will easily do 100,000 miles without further attention, it might see you out !

2. The blocks do have a tendency to crack between the bores, ( particularly during the boring process ) and by the time you reach +.040 it is all getting a bit marginal. Bearing in mind that it is the pistons which are the expensive part of a rebore, you might be wise to consider top hat liners

3.Under no circumstances would I be persuaded to machine the crank to fit a lip seal conversion. Out of 5 engines which I have been concerned with which have had this done, 4 have been absolute disasters requiring a second engine out session and a new crank in each case. Bear in mind the process is irreversible

4.Your exhaust valve seats if in reasonable condition should be left well alone . They are suitable for unleaded fuel , and replacements have a tendency to drop out !

5.Replace timing chains and hydraulic tensioner, and oil pump, as a matter of routine. The slippers are a bit more problematic, as modern replacements have a nasty habit of requiring holes to be filed etc even to get them to fit at all, let alone accurately

6.The bronze drive gear for the distributor is worth replacing, as these have a tendency to wear and you then get ignition timing scatter

[David Oslo]

I concur with Christopher.

Regarding the slippers (chain guides / supports) I changed all of mine a few months ago, sourced from SNG, and chose the highest level of parts (they have their part number w/out suffix & # & * coding system). I carefully compared my new to old parts one at a time before fitting due to concerns I'd read on the forum. Hand on heart, touch wood, I can say that the parts I bought were spot on dimensional copies. Didn't have to file or adjust anything. Two of them were in Jaguar 'wrapping', which obviously helps, whilst the others were reproductions.

Oh, and consider to replace valve springs, valves, guides.

[kgb123]

Thanks Chris and David, I appreciate your feedback and will discuss further with the chap doing the engine work.

On the valve guide, I note there are two options, steel and bronze. I've been quoted for standard K-Line Guides which I assume are steel. What are the advantages of the bronze guides?

Kevin

[christopher storey]

I'm a little puzzled about reference to K line as " standard " . I thought these had some sort of sleeving inside - or am I thinking of something else? Anyway, I would go for standard steel guides, as you may find that the bronze ones have to be reamed to suit which is both an expensive and sometimes chancy process, with a slight tendency for the valves to pick up on the guides in some conditions

[kgb123]

Not sure Christopher, was just reading from the estimate I've been provided. Did some further research on the bronze option, seems its preferred in performance engines and is believed to have better self lubricating properties. Steel seems to be more commonly used.

Kevin

[jag68]

Hi Kevin
By K Line guides are you referring to a bronze guide liner or an actual new guide? K line sells liners - do they also sell guides? I think that the general view of bronze valve guide liners is not to use them. They are difficult to install correctly, and require a chromed or polished valve stem to stand up. When you read the chat lines about them they seem to be a 50/50 proposition - half of the users are satisfied, half are not, unlike new guides where there are much fewer complaints.

Correct me if I'm wrong but aren't the new guides that you buy silicone bronze - I've just done two heads with new guides from SNG and they sure aren't cast iron.

As far as undersize crank journals the Jaguar manual says you can go to .040 undersize for both main and big end. I'm a little concerned about your reference to the size as "round .030" - I hope they are exactly .030 undersize.

The Jaguar manual also says no overbores on the cylinders more than .030 but I've done a couple of 4.2l engines to .040 and they seemed to work fine. You are actually boring out the existing liner, not the block itself. But like Chris - given a choice here, I'd put in new liners and standard pistons.

I also agree with Chris on the seal conversion. The original rope seal works fine if correctly installed - NO CUTTING it shorter - it will all fit into the groove if you work on it. Soak the seals in oil first for as long as you can. I've got a jar in my garage with oil and seals in it for when I need them.

Main head problem is with guide and tappet wear - that's what causes most noisy valves - not bad clearances. You should replace both, or at least try an overside tappet and bore out the buckets.

Terry Sturgeon

[kgb123]

Thanks for your input Terry,
Yes the k-line reference is for a standard liner, not a guide.
The spec is +30 so, just me being vague saying "around"
I checked with the chap doing the work for me, he is saying he'd put standard parallel liners in as there is no damage/cracking to the block. He'd use top hat if there were damage. Would top hat liners be a better option even with no damage? Only adds approx ?20/pot for the additional machining.
Regards
Kevin

[christopher storey]

The problem with the blocks is that the cracks often only appear after the block has been bored - ask me how I know !! Given the minimal cost difference, I would go for the top hats

[64etype]

There's currently a string on Jag Lovers regarding a failure of a Rolon timing tensioner. I'm in the middle of a rebuild and will remove the Rolon unit that I just installed and send it back to the supplier. I will do the same with the Rolon chain and guides (whose holes had to be filed to make them fit). As previously stated, buy only the best quality parts.

Regarding the rear main seal kits, there are many, many successful installations. Terry Lippincot, a well respected engine builder in the U.S. told me he installs them routinely. As far as I know, there are two kit designs. One uses a seal that is cut at one point on the radius. It must be spread open clamshell style and slipped over the sealing surface on the crank, then squeezed back together, whereupon the spring that puts tension on the lip is looped around the seal and the ends attached. The last is a very finicky job that I believe can result in leaks if not done correctly. I also suspect that the split at the cut in the seal could be a leak source. The second kit design is from Bill Terry of Terry's Jaguar. It uses a stiff Federal Mogul Viton seal (no spring) that is in two halves...very similar to the original rope seal in concept, and virtually identical to what has been installed in many, many GM engines. The ends of the two semi-circular halves press together when the machined carrier shells come together. A small dab od sealant goes on the mating surfaces. Idiot proof, and it works. I'm using the Terry's kit. I spoke with Bill who explained that it goes in every race engine he builds and is of course in many street installations. By the way, I had both kits side by side before deciding which one to send back. Finally, a machined crank can be built back to the original spec by a competent crank shaft specialist. This was the first question I asked the proprietor of the shop I used to resize the sealing surface. He walked me over to his automated welding machine (as big as a small car) and explained the process (including dealing with warping and stress relief). He was rebuilding the bearing surfaces in a gigantic electric motor at the time....but had a line up of large diesel crankshafts waiting for repairs. The cost would have been quite reasonable.

[paulsco]

Re building back the journal.

The bearing surface for the rear seal on my crank had been pitted with rust while it was laid up.
Two respected engineering shops told me it couldn't be repaired because the spiral grove could not be recreated.

I have K-Line inserts in the valve guides of my 340 and have had no problems with them in the last 20 years.

Paul

[christopher storey]

Rebuilding a journal, or the tail of the crank , by welding is , frankly, a bodge which should never be countenanced on a work of art such as the XK crank which in all normal circumstances will outlast the lives of both the car and its owner(s). It is quite impossible to recreate the metallurgical composition of the crank , ( or the original harmonics which have to be eliminated by the damper ) and the worst aspect of rebuilding the tail of the crank is that this is the part of the crank which carries the greatest stress .

[jag68]

My experience with the new seal systems is only anecdotal. I've known a couple of guys who have had it done, with no reported problems. I suspect if installed properly it works fine, but the rope seal also works fine if installed properly. From that perspective use of either system is a wash, but having a bit of Scotland in me I find the new system very expensive and ultimately a solution to a non problem. To properly install the new system the machine work to the crank must be correctly done AND the installation of the seal also correctly done. With the rope seal there's only one thing to screw up. For me that's always a bonus.

If it was me, for the cost. (Scotland be d....) I'd install the top hat liners, and never worry about potential liner movement thereafter.

[kgb123]

Thanks Eric, Seems this rear oil seal option polarises opinion with people either for or against. From what I'm reading issues arise with both original and upgrade options largely as a result of incorrect fitting. I think I'm going to stick with the original seal and make sure it goes in properly. Thanks for the heads up on the chain tensioner as well.
Kevin

[64etype]

Rebuilding a journal, or the tail of the crank , by welding is , frankly, a bodge which should never be countenanced on a work of art such as the XK crank which in all normal circumstances will outlast the lives of both the car and its owner(s). It is quite impossible to recreate the metallurgical composition of the crank , ( or the original harmonics which have to be eliminated by the damper ) and the worst aspect of rebuilding the tail of the crank is that this is the part of the crank which carries the greatest stress .

Regarding the tail of the crank being highly stressed, Ray Livingston, a well regarded Jaguar specialist on the J-L site, has convinced me that exactly the opposite is the case. According to Ray, this is one of lowest stress areas on the crank. Bill Terry, who machines this area down to install his Viton seal on race prepared engines will tell you the same thing.

As for weld repairs, I suspect you have a vision of a guy with a stick arc welder glopping on gobs of chicken shit welds. In fact, the process is fully automated with powdered metal of appropriate metallurgy fed at a precise flow rate to a heat source that is carefully controlled. Anything but a bodge. Again, this isn't a highly stressed journal...it's a low stress seal surface.

[David Oslo]

Check out this site, it shows how one company provide machines for automated welding repair of crankshaft journals.

http://www.gleasonengineering.com/

http://www.gleasonengineering.com/the-gleason-process/

And also here, another company:-

http://crankshaftrepair.org/welding/

[christopher storey]

Eric : my understanding is that it is a mechanical fact that that part of the crankshaft which carries the flywheel carries for obvious reasons ( it has to transmit the whole torque of the engine rather than merely part of the torque as the other segments have to transmit ) the greatest torsional stresses. In addition, although it is supported by the rear main bearing , it bears the weight of the flywheel . Thus it is heavily stressed both in the torsional and the bending planes ( although of course I accept that unlike the big end journals and indeed to a different extent the main journals , it does not have to withstand the forces occasioned by firing ) . Furthermore, 6 cylinder engines have unusual harmonics ( which led to many breakages in early engines in the period 1910-1925 ) which cause the crankshaft to wind up along its length and then unwind, and those harmonics have to be damped accurately if the life of the shaft is not to be compromised . Hence, trying to repair a forged manganese molybdenum steel crankshaft by welding is highly inadvisable, and indeed was never countenanced by the factory

[David Oslo]

Stress is relative to the area carrying the load (both in torsion and bending, albeit different formula), and also relative to stress concentration factors such as sharp corners and transitions. Thus an ideally designed and optimised crankshaft (or any product) would have a geometrical distribution that provided the required strength, stiffness, harmonics (etc) for the material used. Putting it another way, the large diameter tail end of the crankshaft may actually be the least stressed part of the crank, if it has been suitably designed.

Look to nature, which is rather fantastic at optimising it's designs. Look at a tree. It's huge at the bottom of the trunk (highest overall loading) whilst it narrows upwards, and narrows even more on each branch (loadings going down the further up & out). But the bottom of the trunk is likely to be the least stressed part of the structure. Subject to a wind load, buffeting, snowload, etc the end of the branches will fail first, then the larger branches and ultimately in a worst case scenario the trunk may fail.

Just trying to explain the difference between loadings and stress in the material....

[rfs1957]

Nothing wrong with metal-spraying and until someone shows me XK cranks with the back snapped off I would have no reserves about doing it. A ?botch?, a technology which is highly successful in - amongst other things - the addition or inclusion of metal alloys specific to such and such a required function or characteristic within a component ? Hardly. I have bikes where cranks have been saved like this and they are considerably tougher and truer than when they were new. Until someone here comes up with a KATIA or w.h.y. analysis of XK crank stresses across the rev-range, discussions about metal-spraying the tail being likely to provoke failure are just bar talk.
The question is whether it is necessary.
Must go down to the workshop and wipe the 2 drips per week that come from my VSE rope-seal. I think of it as my chain-oiler, eh Crespin ?