Opel based Locost 7

[gene]

This is my first post. Nice to be here.

I am building a Locost, based on the book by Ron Champion, if you are familiar with it. It is a home built car based on the Lotus 7. My particular build is in the early stages. I am assembling components now. The finished car will weigh about 1200 lbs. Power for my car will come from a 100 hp Kawasaki ZX9 motorcycle engine, and will employ the engine's internal 5 speed gear box (no-reverse). A central drive shaft will be fabricated to get power from the splined output shaft on the Kawasaki gearbox to the rear wheels.

My questions for this group revolve around the possible use of an Opel (or Chevette) rear end for this project. My search has led me here for a few reasons.
1. I need a simple lightweight unit.
2. I desire a final drive ratio in the low to mid 3s (ideal is about 3.54:1)
3. I require a 4 x 100 bolt pattern,
4. I need brakes that will fit within a 13" wheel (BWA period wheels 6.0" wide)
5. It needs to be cheap, with parts available for rebuilding if required.

So far the Opel rear end looks pretty good on paper. Hovever, I need to know the track, final drive ratio(s). The original Lotus seven had a track of 48.5 inches. The standard chassis locost chassis I will be working with is designed to accomodate a rear axle of 55" (this is one of the reccomended rear ends from an 86 Toyota Corolla. )

The best data I can get on a Chevette, indicates a rear track of 51.2" (1300 mm). Is the Opel the same?

I see the bolt pattern of the Opels listed variously as 4 x 100, and as 4 x 4. Which is right?

I have studied the torque tube issues, and this gives me pause as well, but I think I could find ways to deal with it. The standard single trailing arms on each side of the Opel would be replaced with shorter dual trailing arms, and panhard rod. The main concern would be to build in enough movement for the torque tube to "slide/plunge" into the yoke of the driveshaft. But I think this could be done. Rear suspension travel is only expected to be about 3", perhaps less.

If it turns out that the Opel rears are too narrow to suit my project, do you have reccomendations for me? I Have heard that some RWD Isuzu cars may fit the bill, but can find nothing on them. I beleive I may have even read posts by Opel enthusiasts who made a swap to an Isuzu rear, if anyone could direct me to this info I would appreciate it.

I just recently discovered that Toyota made a 4WD Tercel wagon in 84-85 that had a solid rear end. Anyone who knows anything about these, or where I could get info on these would be doing me a big favor. I can find nothing on the internet.

I invite your creative thoughts and ideas. And thanks for letting me tap into your experience. Gene.

[RallyBob]

Originally Posted by gene 1. I need a simple lightweight unit. 2. I desire a final drive ratio in the low to mid 3s (ideal is about 3.54:1) 3. I require a 4 x 100 bolt pattern, 4. I need brakes that will fit within a 13" wheel (BWA period wheels 6.0" wide) 5. It needs to be cheap, with parts available for rebuilding if required.

1. Reasonably lightweight, yes.
2. 3.44 is the stock ratio, 3.67 on some models as an option.
3. 4 x 100 it is.
4. Stock Opel wheels are 13", drums are 9" diameter.
5. Here's the clincher....parts are unbelievably expensive, and have to be special ordered from Germany. Other than one independent US parts source, the bearings, shims, etc are NOT available in North America.

Oh well, 4 out of 5 ain't bad.

Bob

[jlthunder]

I'm in Montgomery County. Where in Bucks Co. are you? I have a rear end out of a car if you want to look at it(it is currently not for sale) and a complete Car. There is also a guy down the street with a bunch of Chevettes. I can show you where he lives if you want to go that route

Jeff

[gene]

Thanks Bob, that info is most helpful.

Can you help with any of my "track width" questions?
The standard chassis locost chassis I will be working with is designed to accomodate a rear axle of 55" (this is one of the reccomended rear ends from an 86 Toyota Corolla. )

The best data I can get on a Chevette, indicates a rear track of 51.2" (1300 mm). Is the Opel the same?

If it turns out that the Opel rears are too narrow to suit my project, do you have reccomendations for me? I Have heard that some RWD Isuzu cars may fit the bill, but can find nothing on them. I beleive I may have even read posts by Opel enthusiasts who made a swap to an Isuzu rear, if anyone could direct me to this info I would appreciate it.

I just recently discovered that Toyota made a 4WD Tercel wagon in 84-85 that had a solid rear end. Anyone who knows anything about these, or where I could get info on these would be doing me a big favor. I can find nothing on the internet.

[gene]

Thanks, Jeff. This may be helpful.

We may be near each other. Bucks County is in the extrem eastern part of the state, located across from Trenton, on the Delaware River, I am just south of New Hope PA, if you know that destination.

I think Montogomery County is just west of here.

[RallyBob]

Originally Posted by gene Can you help with any of my "track width" questions?

Track width is of course dependent on the wheel width and offset as this is measured from wheel centerline-to-wheel centerline, so I can't help you directly there. But as far as the actual axle width, from 'drum to drum', here are some specs:

GT rear axle width 52 5/8"

Manta 'A' rear axle width 54 5/8"

Isuzu Impulse rear axle 56 3/4"

Manta 'B' rear axle width 56 7/8"

Toyota 2wd pickup rear axle 55 1/4"

HTH,
Bob

[gene]

Thanks Bob. I knew I was in the right place for this sort of info.

based on the specs you provided, the Manta A or B axles would be better suited to my application. Do they have the same ratios and bolt pattern you quoted earlier for the GT cars?

Thx Gene

[jlthunder]

Originally Posted by gene Thanks, Jeff. This may be helpful. We may be near each other. Bucks County is in the extrem eastern part of the state, located across from Trenton, on the Delaware River, I am just south of New Hope PA, if you know that destination. I think Montogomery County is just west of here.

You are correct. It sounds like you are near Washington's Crossing. I'm near Harleysville, PA(between Quakertown and Lansdale, PA). You are welcome to visit anytime, just let me know when you are coming. You are about 45 min away from me.

[gene]

Exactly right! I am in Washinton Crossing. I didn't mention it becasue it is a one stop light town. Who'd have figured someone out there would know it. I am impressed.

Bob has me leaning toward the manta axles now. Is yours a GT or Manta?

Thanks again. Gene

[jlthunder]

Originally Posted by gene Bob has me leaning toward the manta axles now. Is yours a GT or Manta? Thanks again. Gene

Gene

The axle is from a GT. You are welcome to see it. There are others in Bucks County with an Ascona(Plumbsteadville) and Manta(Hatboro) but I don't know what types of spare parts they have.

I know about Washington crossing from the history books and the canal tow path. At least you don't have to pull your mirrors in, in an Opel when using the bridge to NJ My former boss lived off of Durham Boat Road in Washington Crossing.

Jeff

[jeff denton]

Gene, your mention of the torque tube, plunge, and the lower control rods made me stop and think a minute, then I decided I should caution you against using shorter lower rods. I think that would screw up the action during axle travel. Badly, in fact, if I'm picturing this right.
There was a lengthy discussion a while back about the plunge, in the end we pretty much agreed that there is very little, if any, in the Opel setup using the torque tube.
Bob is right about the problem getting parts for the Opel diff. Trust me, I know all about this part... They were very very expensive. Absolutely ridiculously expensive, but I absolutely had to have them so I gladly paid asking price and moved on. You do not EVEN want to know what a ring and pinion costs.
I didn't catch any mention here yet of just how weak the rear end is, I myself haven't broken one but apparently it isn't hard to do, with a little more than stock horsepower. Both diffs I've been into had the pinion bearings SHOT even though the carrier bearings were fine. I don't know why.

[GTJIM]

This car originally had an Opel 2.0 Manta motor in South Africa:

http://www.trademe.co.nz/Trade-Me-Mo...n-41948662.htm

[gene]

Jeff wrote..."the torque tube, plunge, and the lower control rods made me stop and think a minute, then I decided I should caution you against using shorter lower rods. I think that would screw up the action during axle travel. Badly, in fact, if I'm picturing this right."

I am not an engineer, though I play one in my garage. More times than I can remember, I have gotten into trouble thinking some "common-sense" solution would work, when in fact it hasn't. So, I take heart in your assessment that the shorter arms would screw things up.

In studdying the drawings of the rear end it appears that the standard Opel trailing arms are specifically designed to pivot at the same point (forgetting planes for a moment) as the junction of the torque tube and it's mating yoke. As the post you referenced notes, the there is a little spring in there to allow the spines to slide a bit, and still keep tension on these parts.

If I understand your concern, and it is one I have tried to understand better, the shorter trailing arms I proposed to build, would by nessessity, pivot at a different point (and in a different plane, becasue there two trailing arms) than the torque tube splines/yoke intersection, and this set-up would cause binding, or at the very least an excessive amount of sheer/plunge, far more than the original design which moves only about 5MM or so. Is this correct?

My thinking, perhaps flawed, was that a very stiff rear end with 3" of travel or less, might pose little or no more plunge than the standard set up. But the whole issue of binding, still gives me an uneasy feeling. A telescoping driveshaft that bolts directly over the torque tube, might work, or cutting off the torque tube and welding a u-joint in it's place might work as well, but these raise other issues, partiqularly if these parts are fragile, and expensive, as you suggest.

The whole point of a Locost is to build a kick-ass car with the power to weight ratio of a porsche, for a frew thousand bucks out of essentially "found objects".

Perhaps I should drop the whole Opel axle idea, and see if I can locate a Toyota or Isuzu axle. It would be less expensive, and, it sounds like less reverse engineering.

Everyone's comments have been tremendously helpful. I apprecite the insights. Gene