Getting ready to re-install my newly rebuilt engine, Mk 10 Triple SU’s and Manual Overdrive gearbox drivetrain in one of my 72’s! Cannot wait!
Does anyone know what the actual reason for the phenolic disc ‘Engine Mount Insulators’ is? You know, the thin discs that go between the rubber engine mount and the steel mount on the engine…? I’ve always just re-installed them but with this Mk 10 manifold I could use that extra 1/8" clearance even though I’ve already shaved down the carb bells to E-type height.
I’m probably gonna just leave them out - I always assumed they were some kind of Anti-Squeak measure.
I don’t know the answer, but congratulations on your progress. I too had to shave down the carb bells, and in addition I slightly angled the face of the manifold where it bolts to the head (milled to remove 1/10 inch from the bottom whilst just cleaning up the top.
I wanted to mention one thing that I never tried. I’ve read that the engine can be rotated a bit on the mounts because of the slotted holes–you might be able to rotate the carb side down and the exhaust side up. No idea if it works–I read about it somewhere after I’d already scrounged enough clearance for the bells.
I remembered you’d mentioned that you angled the manifold face a tiny bit but I wanted to avoid doing that cause the carbs are already all nicely mounted up and ready to go and I’d have to take it to a machine shop to do it. Did you find that you had to do that even after the bells were cut down?
I’m gonna try the rotation in the slotted holes and see if it can be done – I was thinking I could actually put 2 of those isolators on the exhaust side and none on the intake. That should effectively rotate it a little bit.
As you did with your car, I’m also not using the Series 1 Header tank which I know can be a source of bonnet interference.
Anyway, I’m so close now I can taste it. Just got the throttle linkage sorted and it came out beautifully with the only modification to the original S1 throttle unit being welding on a new arm at a different angle. The rest was off-the-shelf hardware and some sheet metal. I took to heart what you told me a long time ago about not trying to hook the carbs together with accordion links
Mike, I think we make a good team. I make the mistakes, then you do it right.
I wish I hadn’t gone the way I did with the linkage, for sure. Regarding bonnet clearance, I think I did some trial fitting, then milled the flange, then, after installation, noticed I had zilch clearance on the front carby. I then cut down the snouts. I could have done just the front, but wanted symmetry.
Having read about others who had fit triple HD8, and spoken to two individuals directly (including Steven Kee, a former lister from whom I bought the manifold/carbs) I noticed that many folks had no difficulty, but a few did. It was then that I wondered of rotation of the engine on the mounts was the variable I hadn’t considered. I never tried it myself.
BTW, I didn’t shorten my dampers, but I noticed recently on this list (can’t remember where) photos showing that the Mark X damper is slightly longer than the E-type. That’s not surprising given the snout difference, but I hadn’t previously known that the two carbs use different length dampers. I’ve done nothing about mine. I have no idea as to whether it makes a difference, but something for you to consider.
Thanks Frank. I’m gonna do just that. If you and everyone on this very knowledgeable list can’t come up with a good reason not to I’m gonna see what I gain from putting 2 on one side in the rotation department once I get the drivetrain in the car and leave em out if it doesn’t seem to be getting me anything.
Well you definitely disabused me of the idea of linking them together at an early stage… No substitute for experience and I very much appreciate all your help over the years I’ve been picking your brain about this!
So you skimmed the flange first before cutting down the bellls… good to know. I would think I should be okay leaving the flange at this point until I found out otherwise.
I knew about the damper thing and I actually spoke to Joe Curto about it (he cut the bells for me). The longer Mk 10 dampers block the pistons from coming up all the way but only a tiny bit at WOT. SNGB sells the shorter version for E-Types for like $15 a piece. I will probably do that at some point once it’s running.
This is gonna be a big weekend. Drivetrain is going into position for the first time!
Hi Paul - I was just talking about the thin little discs that isolate the metal of the mount on the engine from the thick rubber mount. I doubt there’s any structural advantage with them - my best guess is they are for noise purposes. Jag is famous for that sort of thing. They had Laycock put a corrugated washer (that always breaks and can cause problems) in compact overdrive units to cushion the activation of the sliding member because someone at Jaguar heard an imperceptible click that us mere mortals would never care about
This is interesting. I looked this disc up in the parts manual to see if I could get any insight and apparently 4 of them are required for 2.8 engines… And to add to the mystery, 2.8 and 4.2 as well as all permutations of A/C and non A/C all have different part no’s listed. Obviously this has to do with weight but why did Jag decide that ALL 2.8’s need 4 of these discs and ALL 4.2’s only need 2? Weird, wild stuff…
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The 2,8 (and 3,4) blocks were slightly shallower because of the shorter stroke, Mike - so the discs may be used to lift the block for proper driveline alignment…?
imo, you can use any mount, the height is a bit different, so long as things clear
I am fairly certain the XJ engine is canted down so the back is slightly lower, a lot of engines are also canted sideways, which as I think? is what you are considering (just a tiny bit),guess it will vibrate if not done carefully
I am also interested in throttle connections XJ to tri-carb…but in reverse to you guys
have put an XJ motor in a 420G, and I dont like my throttle conversion, even though it works fine,
there is some engineering issues ( the 420G throttle plate flexes and the engine is pulled towards drivers side by throttle cable!)
it presently has twin HS8 carbs with Manual choke, hopefully I will soon find time to place 3 x HS8 on a 420G manifold, with manual choke, but I would like to get the throttle concerns sorted first
may hope to exchange a few “throttle” pics…sounds like youse all got the secret knowledge that I need !
I have many spare HS8 and HD8 carbs, and a couple of 420G manifolds
That’s what I was thinking as well - maybe it wasn’t an anti-squeak thing at all… just a height adjustment… or
maybe a little of both.
The other thing is that the rear transmission mounts are spring-loaded as we all know. So even though it doesn’t move alot the engine/transmission assembly definitely pivots on the engine mounts – maybe that had something to do with why they exist as well. Interesting…
I’ll post some pics and parts list for the throttle conversion from US Spec Series 1 Throttle linkage to 4.2 Mk X triple SU’s but I don’t know if it’ll help you with your conversion. Looking at the parts manual, that linkage may be peculiar to our Zenith/Stromberg equipped carbs.
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There is unavoidable flexing in all mounts under torque, Mike - which is one reason there are universal joints…
…but an initial alignment is still required. Whether the discs are relevant for this purpose, or some other, seems lost in the mist of time - gone with the skilled hands that put the cars together…
The stroke on the 2,8 required the crankshaft to be ‘lifted’ some 0,4" - but exactly what this entailed for the rest of the set-up, I don’t know. Like different engine mounts or whatever - but Jaguar laid great effort on compatibility, to reduce part inventory. Though peculiarly; part numbers are sometimes different for identical components - making sorting chaff from the wheat difficult…
In short; the discs’ purpose is one of those things that may only be clarified by people long dead…séance anyone…
Wasn’t sure I could contribute anything worthwhile to this discussion, but then I looked and the XJ12 has them as well.
Both the factory manual and the Haynes manual say to ensure they are put back in when you install the front mounts, though not giving a reason for their existence.
Some here may not be aware that it is important in any car with a driveshaft, that the crankshaft/transmission centerline be parallel to the differential pinion centerline, because the u-joints are not constant velocity joints, and any misalignment will cause some amount of vibration in the car.
So whether they are an anti-squeak device, or for alignment of the engine with the rear differential, I would put them back in.
