MG Sports Cars

Thanks for the compliments guys. I don't have a really good means of weighing the unit but I'll see what I can set up in the next day or two.

I thought about double shear on the shocks but it's not that easy to do because of the way the diagonal brace attaches. I think the extra strength of the stainless bolts will prove adequate though. In the next version I'm considering a new design for the lower control arm rather than using cut down Jag units and this will save considerable weight and allow a much better shock mount as well as more optimum positioning. The main cross member can be improved also, and tubular half-shafts will remove even more weight. Ventilated brake rotors are another possible option, and with the unsprung weight reduced even further the ride is bound to improve even more.

I know the Jag brakes have been berated but I've come to realize that this really is a very good system, especially for the day when it was designed but no less so today. For instance, the brake pads can be changed from under the car with nothing more complicated than a pair of needle nosed pliers. Two stainless hairpins are pulled, two cross pins slid to the side and the pads slip right out. The e-brakes are a puzzle to assemble but simple enough once you know how, and as long as you check the main pads often enough to make sure the rotors don't get scored, brake maintenance is no big deal.

I'll have some more information once the unit is bolted into the car but that might not happen right away. I've neglected certain other duties in order to reach this point as quickly as possible and may not get back to it for a little while. In the meantime I've just gotten word that my head gaskets should be ready to ship by about Wednesday and I'd like to finish assembling the engine.

Jim

Last night I installed the IRS and it was a bit of a job. Lines and wires had to be moved, the two outside upper corners of the battery boxes had to have bends put in them to allow the bolt heads of the upper coil-overs to clear during removal (this was not completely mandatory, removal of the spacer tube first gives enough clearance, but who wants to muck around with that?) and the whole unit had to go in and out several times before I had the proper tank clearance. It seems those torque straps that I added to the rear need a little space where the gas tank resides so I had to ding in the front edge of the tank in a couple of spots. Not enough to affect tank capacity, but not the sort of thing you want to be doing on a so called bolt-in installation either. So if I make any more of these a slight re-design would be in order to get the correct clearances. Oh well, these things are to be expected on a prototype. The good news is that it is now in place and the jack is out. I won't be working on it any more until after the weekend, then I'll secure it in place and hook up the brakes, which should be an easy task as everything was prepared in advance.

I had a question about the weight and I'm happy to say that I found the opportunity to weigh everything. I wish we had a page for weights and dimensions, but for now, the IRS is 90 lbs heavier than the stock MGB rear suspension, including springs, shocks, and hardware. Not bad if you ask me and that can be reduced to less than 50 by using tubular half-shafts and after market lower control arms, further reducing unsprung weight in the process. The stock suspension, complete except for sway bar is 235 lbs (axle is 160) and the modified Jag IRS is 325 lbs. For my application this will nicely offset the additional 82 lbs from the iron block 340 engine in the front, brakes are now fully upgraded all around and there is plenty of extra power to more than offset the additional weight.

I added bump stops to the coil-over units and rear suspension travel is now a full 8 inches. Quite exceptionally really for a car of this sort. The spring rate and shock settings seem a good combination although some might think the springs a little soft. I upgraded the springs on the Roadmaster from the 225 used here to 250 so this should give us a good comparison. I did find that the use of Corvette rear wheels requires a little more width hub-to-hub so 3/4" can be added to each control arm and half-shaft, getting us within 4" of the original XJ6 width. The suspension geometry looks very good.

Next week my head gaskets should finally arrive and I can finish assembly of the engine then it will be on to the modified 200r4 transmission and the intake manifold. Those will take some time but maybe not all that much.

Jim

Been nearly a week since I got the IRS bolted into place and I've hardly even been out to the shop. I'm just not as durable as I used to be a few years back and I'm not real used to that kind of work these days. But the good news is that the head gaskets got here today so now I can get on with checking valve clearance and pushrod length. If I'm real lucky I might even be able to put the pan and valve covers on, but I'm not going to count on it. It's very likely I'll need custom pushrods. I sort of doubt I'll have to cut valve reliefs though. Should know more in a few days.

On the rear, I'll have to mark and drill the mounting plates and get those secured, hook up the brake line and e-brake cable (already shortened) and get a pair of springs for the e-brake caliper return since I used mine on the Roadmaster last week. Then I need to start thinking about what I'm going to do for wheels since the Corvette ones are just too close (I think).

Then, with everything finished on the rear (except the wing actuators) it will be time to get back to the transmission and the intake, both of which will take some dedicated thought. Maybe after the meet in Durham I'll have a little time to put aside for that exclusively, wouldn't that be nice?

Jim

Jim, Buy a set of billet same bolt pattern spacers. They are 1 1/2". $69.00 a pair on ezaccessory.com.




Edited 2 time(s). Last edit at 04/16/2009 05:15PM by mgb260.

Thanks Jim, do they make them in 1/2" or 3/4"? I believe either would give me what I need. 1-1/2" might work but I haven't had the chance to see how much clearance I have to the outside yet.

In the long run I need different wheels and I want something a lot lighter, but even then, there's going to be a wider selection on the Corvette wheels.

Jim

Jim, best company I know of for spacers is Skulte... www.skulte.com That's where I got mine. There's two types -- 1st type slips over the studs & gets sandwiched between the wheels & hubs. Those are good to about 1/4". Some folks will say 3/8". The 2nd type are the ones like Jim N posted. They bolt to your existing hubs & have their own studs for the wheels. Skulte can do them 3/4" - 4" (although I can't imagine using any that thick).

Note that there are cheaper places, but Skulte has a reputation for quality.

Jim, 1" to 3".

I appreciate the help guys. First choice is going to be different wheels though, these are awfully heavy. Plus I'm not a real big fan of wheel spacers and then there's the unescapable fact that the spacer has to be at least as thick as the original lugs are long, so that probably means 1-1/4" at best. Finally, if I add the cost of the spacers to the wheel purchase budget I should have some pretty decent choices, and might be able to sell the Vette wheels also. But I do need to bolt up the wheels and look at the outside clearance before doing anything else. Perhaps I can get that done today.

Jim

I certainly understand the desire to avoid spacers if you can... but RE: the spacer has to be at least as thick as the original lugs are long... I don't know of a reason you cant cut them off to not extend past the spacers.

If you do end up going the spacer route, note that you should use ARP or similar studs IMO -- so there's that expense too. Prices on studs are all over the board but seem to range from about $25-80 for 10 of them.

I got the IRS bolted in so I decided to install the wheel and tire to check clearance. Below are photos, I checked clearance in the entire range of travel. My maximum outside clearance is 1-1/8", measured at the sides of the flare under heavy compression, and the tire just squeaks past the bump stop hump (slightly doctored) and then hits the sheet metal at full compression. So to center it I could come out 9/16" and should be just about there, or I could come out as much as 3/4" and look better maybe, but be closer to rubbing. Any more is going to be too much.









I noticed that the Vette wheels have a space between the lugs so an adapter thinner than the lugs (1-1/8") would work. One intriguing possibility occurred to me as I was looking at a damaged Jag IRS hub flange. It is .470" thick and that would probably be enough. It would have to be counterbored and have holes drilled and countersunk for the other lug pattern, not a real problem. But I only have one of them. I also have a set of 5/8" flanges on the axles of the old MG axle that came out of the car. They have a 5 lug pattern but it is 4-1/2" Probably too much machining is needed to use those though since they would have to be cut away from the spline hubs but I think they could be made to work. I 'll have to give it some more thought, the answer is there somewhere (yeah, like buy wheels with a 40mm offset instead of 56!)



Edited 1 time(s). Last edit at 04/17/2009 04:01PM by BlownMGB-V8.

Jim, did you ever get a chance to weigh a bare 340 block?

Greg

Yes Greg, the 340 block weighs 82 lbs more than a bare 215 block.

Jim

Finially the correct copper head gaskets are in and I've been able to get back to work on the engine. While waiting I ported the oil passages in the front cover and in the lower oil pump housing. For the uninitiated, the entire Buick V8 line including the 215's and the Rover derivatives all come up a little short when it comes to oiling. (Nailheads excepted) Nobody seems to know why the oiling system was compromised with small passages and many bends but fortunately for us the problem was recognized long enough ago that the remedies are now well proven, and essentially consist of enlarging passages and rounding corners. In the block, the suction passages (2 intersecting straight holes) get drilled out larger, to 9/16" or if you dare, 5/8". The stock pickup gets tossed in favor of a 5/8" ID pickup, the output oil transfer passage in the front cover gets drilled out from 7/16" to 1/2" or somewhat larger, and the front cover, oil pump housing, and lower cover all get ported for flow, primarily by rounding sharp edges and enlarging ports where possible. All of this boosts the oil flow through the engine enough to satisfy most performance needs, and the high volume pump modification is no longer considered a good addition as it causes extra stress on the distributor drive gears. When the oil pump is assembled careful measurement and proper selection of shims (available from TA Performance) allows setting of gear end play to .002" and addition of their booster plate stabilizes the housing. Finally, it is essential that oil losses inside the engine be controlled in order to avoid starvation of the rod bearings at the rear of the engine. First step here is to tightly control rod and main bearing clearances. Buick engines run tight clearances and figures of around .0015" are the norm. Lack of attention to the cam bearings can also cause oil loss, so these must fit properly, and losses from the rocker assemblies must not be excessive. However, an indication of 10 psi per 1000 rpm is usually considered acceptable. So with that mostly out of the way I turned my attention to the valvetrain.

With the heads and head gaskets in place selection of proper pushrods becomes the next issue. This brings up another little item. Did you know that in the trade, the SBB cam is referred to as a reduced base circle (RBC) cam? And this applies not just to the 340 but to the entire SBB line including the V6's, the 350, the 215 and all the Rover versions. This is because they all share the same crank to cam centerline distance and all but the V6 and 350 share the same cam. It's called a RBC cam because due to internal engine clearances and the cam journal sizes, any increase in lobe lift is gotten by grinding deeper into the base circle of the cam, leaving the tip of the lobe at about the same spot for all grinds. Why is this important? Simply because it means that any lift change is going to require new pushrods. This, and a lack of general knowledge about this one simple fact accounts for a great deal of frustration over lifter tap after a cam change since that extra lift just ate up your safety margin in the lifters.

So then for me the question was, what length pushrods do I need? Luckily I found some old tubular pushrods and screw tips from some motorcycle rockers and made up four adjustable pushrods which I used to determine the length (9.180") plus a nominal preload (.040") plus a safety factor (.030") giving me a pushrod length of 9.250" and these were ordered from Smith Bros. I'd much rather have them a shade long than too short and the lifters can accommodate nearly 1/4" of preload. Next I needed to know how much valve clearance I had to the piston. Recommendations are .120" on the intake and .090" for exhaust. So using an old set of lifters which had been modified as adjustable solid lifters and set at .020" compression (internal spring replaced with an adjustable bolt and nut), I placed a bar of clay across the piston, installed the head and the adjustable pushrods, took out all the slack and cranked the engine over by hand. On removal I retrieved the clay, sliced it across the closest approach of the valve to piston and took measurements. Photo below. A 1/4" tool bit is used as a visual reference showing a clearance of approximately 1/4" so with the 10-3/4:1 pistons and .500" lift there's a large safety margin. Of course other cams will be different, especially one with more overlap.

Jim

I got a chance to do some more work to the 340 finally. First I pulled one head and dialed in the degree wheel.



Then I cleaned up the deck, heads and gaskets, put a thin smear of Right Stuff sealant around the oil and coolant holes and along the lifter valley and torqued the heads down to 65 ft lbs. (ARP recommended specification) Note, the stock spec for the 340 is 80, but the ARP studs are fine thread, have moly lube on the threads, and the heads are aluminum, all of which lowers the required torque. It feels real good at 65, that's adequate pressure to bed the o-rings, and I got a fine squish of sealant in the right places telling me that all is well.

Next I put an indicator on the valves and degree'd the cam.



The results I got were not in exact compliance with the cam card, and I also found I had 5 degrees of slop in the double roller timing chain. Compliments of the align bore. But before I rush out and buy yet another timing set I've asked the Buick V6 guys about the tensioner used in the V6. Don't know if it can be adapted or not but that would be a handy solution if it could. I also found a casting flash on the big end of the crank lines up just about perfectly with a rib in the bell area at TDC. Very handy.



Jim

"I also found I had 5 degrees of slop in the double roller timing chain. Compliments of the align bore"

Not necessarily, I noticed that Dale takes extra pains to remove metal from the caps rather than the block. Some (maybe most) of that may be in the chain.

I tried my best to get Tim to advance his cam 4 degrees while we were reinstalling his timing chain at Flying Circus.

"Not necessarily, I noticed that Dale takes extra pains to remove metal from the caps rather than the block. Some (maybe most) of that may be in the chain."

I wasn't blaming Dale. You should have seen what he had to work with, right, left, right, the main saddles looked like a snake and the caps were off a different block from all indications. It's a true testament to his skill that he was able to bring it in at all. With it perfectly straight there was just a bit of color along the parting line on one side of the center main. Not absolutely perfect, but as there are no heavy loads there, plenty good enough. I sort of expected this problem but I went so long without working on the engine that I forgot that I planned to check it with the unused silent chain set before buying a roller set. Now I have extras.

Jim

More progress:



$30 cut square and bent to fit. I did the trimming. The fit is perfect, a little sealant is all it needs, plus the ports and bolt holes, which I will cut later. In the meantime it makes a perfect base for fitting up pieces to the intake and tacking them, while keeping swarf out of the motor. So next I need to get an intake gasket for port matching and buy some aluminum plate to make up the intake. I've got some feelers out for a TIG and hope to have that sorted out in a week so things can move forward.

The chain slack is 7/16" which translates to a .008" oversize timing set. Anyone know a good source for that? TA wants $145+ which seems a little high to me.

Jim

Cloyes used to do oversize chains. I think the V6 tensioner would work, I think it pivots on one bolt if I rememeber correctly.You need a tighter chain. Wouldn't that be an undersize.



Edited 1 time(s). Last edit at 06/19/2009 04:43PM by mgb260.

Funny thing about that, I quite agree.

Jim

Jim
I recommend when you cut your ports, make them slightly smaller then the ports in the head. Then wait untill after you have machined the mating surfaces, before opening up the intake ports to match the head ports. Reason is machining/decking the mating surfaces will alter were the ports align.
I found it also helpfull to build the intake without the gaskets in place. It gives you a bit of wiggle room to work with when machining the mating surfaces. Its always easier to remove metal, then to add it back on!
The TIG welding will shrink the aluminum around the welds some. As long as you can keep the welding temps fairly stable, it should only require a minor "scimming" of the mating surfaces.

Bill



Edited 1 time(s). Last edit at 06/20/2009 02:05AM by MG four six eight.