MG Sports Cars

Thanks Kevin, lots of good info there. Afraid I don't have a fax, the blasted things break and seem generally unreliable so I try to make do with email.

As far as the metalurgy goes I do have some practical knowledge about it, enough to know that a reliable repair would be real tricky. The likelihood of a failure from the damaged area is actually pretty small the way it is assembled, but certainly greater than with an undamaged part. I think we should keep looking for one.

Tie bars: I'm with you on that, absolutely. For the torsion braces though (anti-climb bars) I think crude vector analysis allows us to control the rotation in two separate axis rather than combining them with one link (per side) across 2 or three planes (running at an angle as you described). It seems simpler (to me) and easier to understand and implement, if we take counter-rotation around the drive shaft and separate it from counter rotation about the half shafts. That way we can control the rotational motion about the half shafts via the forward pivot of the triangulated LCA, (although this could arguably induce squat or hop - I don't think it should if the pivot points are on the same centerline) and control rotation about the drive shaft via the top mount if the special top bolts are adequately strong and perhaps with additional small braces from the outer ends of the top mount to the rear tie bar if not. Admittedly it is not as elegant in terms of engineering by combining functions but at least that way we don't have to deal with calculating the correct angle of the strut in 3 axis. Which I really don't want to do anyway. I guess you could say that the stock cage also has the lateral braces built into the cage itself which then puzzles me as to why the anti-climb braces need to be angled outwards.

But let me reassure you about the top mount. Either the top part of the cage will be used, or a stronger counterpart fabricated instead. The planned fabricated part will be tied into the shock and hanger strap mounts with isolator mounts and have mounts for the coil overs so it should duplicate the stock cage in most respects, but I won't know the exact configuration until I start building it.

I hadn't given any thought to the ride height, that's something maybe we can try to address next weekend. Certainly it influences many other decisions, and is largely decided by factors currently beyond our control such as final engine weight and front suspension configuration, but we can make an educated guess. We also need to accurately measure driveline angle.

Use of the car? Ah yes, that is likely to be quite varied. It is likely to see duty as a driver, show up on a road course here or there, be entered in a few autocrosses and even make a few dragstrip passes. It's basically up to the person in custody of the car at the moment. So we should consider all possibilities as far as it's feasible to do it. Odds are it will end up being a little over built, but that's better than the other way around.

Jim

Jim,

I may be able to get an old scanner working and hopefully be able to post the drawings and info directly on to this board possibly later today, if I can get my son to help gettting the scanner linked to the computer.

I'm sure you are going in the right direction and some extra visual info may assist.

Kevin.

I will be leaving in the morn for Alcoa and than Florence. Anybody who wants to help tear down the 455 and other stuff, I'll invite you to Jim's.

Steve

Steve I will be looking forward to your arrival. Hopefully it won't rain any more and the drive to the shop will stay dry, I'm working on getting some gravel for it but it hasn't happened yet. I got the EIN number from the IRS and gave it to the bank, and there's some paperwork I need to give you. We'll tear town the 455 and see what is needed on it, and maybe if we have time after that we can do a little sheet metal work, or calculate the axle lengths that we need. Or, I guess we could just sit around and drink beer.

Jim

Sounds like fun. Will not get there till after 6 pm. Traffic may make it later. Will leave here at 8 am and should see Dan about 1pm. I think it is about 4 hours from there to you.

Steve

Hey Kevin, maybe you can answer a question for me. If we assume a stock ride height for a '69 MGB-GT would you be able to tell me how much space there should be between the Jag differential top mounting pad and the floor area of the car above it? (disregarding the differential bulge that is in the panel) That would really be a big help.

Jim

Jim,

Sorry I've been busy this week and not been able to get the scanner working, the socket for the USB lead appears tp be damaged.

Re you query re the relationship of the diff to the body of the car, frustatingly one of the documents I was going to send, is a diagram covering this subject, tomorrow I will try doing close up photos of the stuff I want to send you.

The diff height is calculated by setting the rear suspension at its optimum ride height, ie where the geometry of the suspension will be under load and then calculate the required ride height of the car, say 14.5"-15" centre of hub to chrome strip and the difference between the diff and its mount position should be clear. The standard ride height for the suspension itself ie the distance between the coilover top and bottom mounts should be 11.75" under load. you can substitute a piece of angle iron with holes 11.75" apart.. Your problem is going to be that you don't have a top mount position at the moment to use as a reference.

I'll try and send the digrams tomorrow which should help to clarify what i'm trying to describe.

Pic may help to explain what I'm saying.
Hopefully will send other docs tomorrow.

Kevin.

Thanks Kevin but I don't quite understand. At normal ride height shouldn't the half shafts be horizontal, or parallel to the ground? That would seem right to me. (thanks for the measurements btw) Preliminary measurements indicate that the half shafts and LCA's will need to be shortened approximately 4" on each side. Certainly not difficult, but as I've noticed that the two are not quite parallel it would seem that taking an equal amount out of each one would change the camber. Would that be correct?

We've made great progress so far this Roadmaster Weekend. Steve and his brother Eric have been here since Thursday evening and we've got some really interesting information for everyone concerning the engine. I'll give a more complete report later, perhaps Sunday. But as a teaser, we weighed the short block and it came out at 300lbs.

Jim

Jim,

Sorry if I wasn't explaining it very well, if I was standing next to you with the car it would be very easy.

The angle of the wishbone should angle down from the diff outwards as per the pic of the red car, whether shortening the wishbones and drive shafts equally will have any effect on the geometry I don't know, but this seems to be the accepted way of doing it.
I would have thought that the geometry would remain the same at standard ride height but whether there would be any change under bump or rebound would need calculating,

I have attatached the documents I previously mentioned which hopefully you can read, if they are not clear enough I could re shoot them in high definition so you can blow them up, if you save them to your my pics folder, just let me know.

Re the setting of the diff position, you could mock up the suspension using a bit 3" x 2" timber and use that tomount the diff and the lower wishbone with the suspension height set with the angle iron as suggested,you can then measure from the hub to the chrome strip position to see where your diff should be sited.

Kevin.

Jim,

Sorry posted a house plan by mistake.




Kevin.

Jim,

Did some surfing and came up with a couple of Jag installations.

Those look good. we did some closer measuring and came up with about 6" per side that needs removed, that should be within 1/4" or so. Still more measuring to be done, including the drum-drum width of the old axle. I want to get an accurate measurement of the vertical distance between the half-shaft and the LCA at each end, and that will tell me how close we are to being parallel, and also tell me how critical it is to calculate any difference in the amount to be removed both places.

The 455 parts that need to go to Dale Spooner are loaded up on Steve's trailer and went out early this morning. That includes the block, crank, damper, flex plate, rods, pistons and two sets of heads. The engine is a '70 and the head casting numbers match, but they are bare heads. We tore down the 430 to get the valves, springs and such and because the casting numbers indicated one was a big port head and the other was a small port head but as far as I could tell the ports were the same and measured bigger than the '70 heads so we sent them along figuring we'd just let Dale pick the best ones. Naturally if we do manage to get the aluminum heads it won't matter but that hasn't happened yet and I like having a backup plan. By the time you read this Carl will have the parts tucked away in his storage building and Dale is making the trip down there every few weeks so with any luck they will be in his shop by Christmas or shortly afterwards.

Here are some engine component weights, as measured on a digital shipping scale:

Complete short block minus flywheel, starter and engine mounts: 300#
Bare block: 177#
Crank: 66.1
1 rod and piston: 4.0
cam: 8.8
Cover and pump: 8.2
Damper: 6.8
distributor: 2.0
timing chain and gears: 1.8
iron intake: 48.9
bare head with rockers: 57.1
flex plate: 4.2
pan: 7.0

I realize that adding up the weights results in an error of 2 or 3 pounds (we were at the limits of the scale) and we'll take a closer look when we have clean parts to weigh during reassembly, but it gives us a better look at the weight we're dealing with here. We came up with 465 lbs for the complete engine minus starter and flywheel, where we had 500lbs for the 430 similarly equipped. This would seem to indicate that there may indeed some basis for the claim that the '70 455 is 50 lbs lighter than later engines. At any rate anyone would have to admit that this is very light for a big block motor. Add flywheel and starter and we're still real close to 500 pounds. On their website TA performance states that their aluminum heads are lighter by 30 lbs each. They also state that their intake is 30 lbs lighter. That would get us down to to around 410 lbs depending on starter and flywheel used. If we can manage to put one of Ted's suspensions under it, we'll be down to an effective weight of 330, which is as light as stock!

But even if we use the iron heads and the stock suspension (I'm sure we can come up with a used alloy intake) if we take into account the heavier Jag IRS and the rearward weight balance of the GT body, our front to rear weight distribution is going to be right on the money, and the only real issue we will have to deal with is an extra 150 lbs on the front of the car. Well guess what folks? I happen to have a stray set of springs that have wire the same size as Huffaker -1" street/track springs but are a couple inches longer. I think that's "Problem Solved!" I'm not real sure what they came off of, but I highly suspect it's TR6 related.

So that's a lot of progress for a cold winter weekend. We actually did have some heat, courtesy of a propane tank and my home made pipe bending furnace and that was enough to take the chill off and give us a stove to sit around for breaks. Maybe by the February meet I'll have the gas furnace operational. In the meantime this should do for December and January is at Ted's. It looks like the December meet will be back on schedule, the weekend before New Year's Eve, and Ted's Winter Party is January the 26th. and that is consistent with our "last weekend of the month" schedule as well.

If anyone would like to learn how to do a front end kingpin renewal, maybe bring parts for your own car or use cores I have on hand, swap them out and send the cores back, I have the tools and the reamer and have done that job before. It's not complicated or difficult. We need to at least inspect the GT kingpins and possibly renew them. Just bring a rebuild kit to the December meet, I'll show you what to do and help you make sure everything is done correctly and you can do both sets at the same time. That would help put us a little ahead of schedule, which is a really good idea since we're bound to hit unexpected delays before the summer V8 meet.

Jim

Folks, I've got the draft of the liability release done for whoever drives the car or takes possession of it. Bear in mind it's a draft and can be changed, but it's something to start with. Those of you who are interested should have a look at it and post your comments. It's written in plain language rather than legalese. I could have done it either way but I don't see any reason why its meaning shouldn't be perfectly clear to anyone who signs it. It says pretty much exactly what any conventional one would. Anyway, here's the text:

Assumption of Liability

I hereby assume all liability for anything that happens with the car, (MGB Roadmaster) except what insurance will cover. I fully understand that we’re talking about dangerous equipment here and I’m putting my life at risk by operating it. Not only that, I may blow up the entire neighborhood in the process. Might as well hold a loaded gun to my head with my finger on the trigger, nobody is making me step on the gas pedal. I’m fully qualified to know if the car is safe or not, and by signing this I’m saying it is as safe as it is reasonable to make it and safe enough to satisfy me. If it turns out that I’m not qualified then I lied about that so I could drive the car. If you don’t believe me check my signature. I also don’t have any idea whether I’m even qualified to drive the car. Most likely not. I expect it to go like a bat outa hell, and be faster, quicker, and more vicious than anything I’ve ever even thought of driving before. I’m looking for a thrill. Probably a real bad idea to even consider driving it, but that’s exactly what I plan to do and if it rears up and maims or kills me then I have nobody to blame for it except myself. Not only that, but my family and friends have nobody to blame except me. This paper puts it all on my shoulders and I’m agreeable to that. If I try to say otherwise I’m lying. Either that or I lied when I signed it so I could get to drive the car. Either way I’m taking full responsibility. If the guys who built it made a mistake somewhere and that causes an accident, injury or death I’m not going to blame them for it. They’re doing the best they can and for something like that to happen it would have to be beyond their control. So I’m not going to come around asking them to share the blame. In fact, I’m sure enough of what I know about cars that I’m going to assume all of the risk any time I’m operating the car or while I have it. In fact, even if I loan it out or if someone takes it without me knowing it I’ll take responsibility for it. You’d better believe I’ll make sure there’s proof of insurance and the registration is valid. That should just about cover it, and if there’s anything I’ve left out I’ll take responsibility for that too. And if some judge says there’s any part of this the law won’t allow that’s fine, but the rest of it stands.

This is a legal document, so it’s to be interpreted in accordance with Kentucky Law.
Signed and dated below:

--------------------------------------------------------------------------- ------------------

I know it's not what you're used to seeing, but I don't see much point in trying to sugar coat the facts. Anyway I look forward to comments.

Jim

Here's another option.

Jim, I think that pretty spells it out in language that we all can understand, no "party of the first part" etc. Even this old Okie gets the point, if I drive it and break it I fix it, and if it kills or maims me it's my fault for being there in the first place.
An interesting linkage in the photo Dan posted. That little Watts linkage does clear up a clearance issue with a lower mounted radius arm on that chassis, but requires a custom hub carrier on the other hand. I'd think we would have room for a radius arm pretty much in the location of the original leaf spring. Using poly or rubber/steel bushings would allow for the slight amount of side to side movement required as the IRS works.

Actually the "break it/fix it" part gets put in the custody agreement which I haven't started drafting yet, but I have given it some thought. There are a few issues to work out on that yet. Nothing that can't be done though.

Dan, that is one thought provoking picture. The Watts link on top is just what I was thinking about. I can't see that it's going to totally control fore/aft motion of the upright but the triangulated LCA would do that. It would however do a good job of controlling rotation of the upright about the LCA pivots induced by fore/aft motion, in effect absorbing half of the accel/decel forces. In doing that it could possibly eliminate the need for the LCA triangulation. I'd like to hear Kevin's opinion of that. If we add the top link can we lose the lower strut? The reason I ask, is that in doing it that way we might be able to keep the battery boxes, beef them up a little, and tie them into the front tie bar. That would make a very strong reinforcement to the diff mounts, and since the battery boxes do provide some body stiffening I'd like to be able to keep them.

As far as custom uprights, yes Bill you are at least partly right. We should be able to heliarc a pivot bracket to the top of the stock ones and do the same thing. Guess I need to finish up that TIG rig.

Jim

Jim,

Pretty sure that is the Contemporary Classic Cobra chassis I mentioned a while ago, it's certainly the same set up for the Watts linkages, I used to see a few of these as a friend of mine was the UK agent for Contemporary, and built some superb cars that you would be hard pressed to tell from the original.

The Watts linkages were used I believe because there was no room on the chassis for the traditional lower links, I still feel that it would be a lot more work to try and adapt the watts linkage than just fitting a pair of triangulated radius arms and not sure there would be enough meat in the top section of the standard hub carriers.

Re the battery cages, I'm fairly sure they are going to have to go if you intend to run with rear brakes!

Keep up the good work,

Kevin.

Thanks Kevin, how were the Contemporary Classics cars for laying down power and avoiding wheel hop? Do you know how they behaved? For instance, when mashing the loud pedal did the rear of the car squat or hop? It would sure be helpful to know that as well as what kind of HP or torque they were handling.

That bell section of the stock upright is heftier than it might look. (No cracks btw) I've not done any measuring but the edge looks somewhere between 5/16 and 3/8" thick and I expect it gets thicker towards the bearings, so a chunk of say 5/8 or 3/4 plate cut to match the curve of the bell should spread the load well enough. It might be possible to tie the links into the shock mount holes on the front and the shackle mount on the rear.

Jim

Jim.

Most of the cars my late friend built were Ford 427 side oilers as per the originals and had 450-550BHP and handled that sort of power without drama.The original cobras just had a lower wishbone and a transverse leaf spring as the top link. I personally have not heard of an IRS car suffering from wheel hop, with the suspension properly located it should just sit down and launch. I used to have back in the late 70's a Jaguar XJ12 coupe and this had the most unbelievable traction, it had a power lock diff that helped and one year we had heavy snow it got me past all the other cars stuck on the hill out of our valley, I just pulled out on to the virgin snow in the centre of the road and drove up the hill. no other cars made it this being in an era before the urban 4 x 4's.

Kevin.

Thanks Kevin, that is most helpful. That also seems rather consistent with the T-bird layout, where there is a massive LCA along with a small UCA but no struts. Interesting approach to be sure. Well, I've been singularly unmotivated to do anything at all the last few days and the tasks I have immediately at hand will prevent any real progress on this for a few days more, but I'll see what I have in the way of materials for an upper lug at least. Perhaps I can get some more done on the tig as well. But mostly I need to make room in the workshop for a job that's coming through. We'll be setting up a prototype line all the way across the building and that means I have to move almost everything and the 'things' have not been cooperating by getting finished. For instance, my roadster is down for brakes. When I converted it to '73 Mustang front brakes I thought the parts would always be available but not so! They've redesigned the hub and rotor into a one piece assembly and I've only found one NOS two piece unit. It's very discouraging when you have to fight a job that way, and if it was only that one it wouldn't be so bad. Just my luck, there's three of them. (Not the RM, but they do keep me from moving it out of the way) Some weeks things just fall into place, and then there's last week. Maybe this one will be better.

Jim