DIY Dyno Engine Cradle/Coupling

[RRBD]

Thanks Bruce.....

I have some literature from Stuska and it appears if they have gone to the cart style layout as well.
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It looks like they have something similar to a mid plate, that I'm assuming is universal and that you have adapter brackets for each specific style of engine that locate onto the "mid-plate".
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I agree with Dave on the DTS comment, the connection should have a slip yoke of some kind.
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I have been laying out a set up in my head and it would be pretty simple to have a drive flange coming out of the absorber that had the same geometry as the flywheel end of an old SBC, so a Flexplate can be used and then have another plate that locates off of the "pilot bearing hole" to speak, which has two bolt patterns;SBC flexplate and another for the driveshaft "yoke" of choice. The flexplate would be sandwiched between the two.
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A Chevrolet Flexplate and a small starter from say a 1998 chevy would make the starter portion a breeze.
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How heavy of drive shaft would be needed?
Cv joints or would u-joints okay?
My first inkling would be to build the shaft from a front shaft form an older (pre 80's) chevy 4x4, maybe with girdles instead of the straps. Since there is not any torque multiplication involved on a Dyno, I thinks it is reasonable to assume it would work, if torque was limited to under 900 ft lbs just to be safe.
-Lets hear more thoughts.......

Scott

[86rocco]

may be of interest to you. My buddy's Stuska dyno is similar to this but without the elastomer coupling, instead it has a universal at both ends of the shaft and the shaft has a splined joint in the middle.

[bruce]

In my opinion you need some type of isolation from the engine to the dyno ie elastomer coupling. I know lots of people out there are not using one but I would guess they have been lucky and not cracked or broken cranks? I have a very good book here that I purchased on dyno design (course I can't find it in my office at the moment) and it dedicates a whole chapter on this subject alone dealing with harmonics. On my dyno I use a lovejoy coupling and my engine mounts are moveable to align the engine to the coupling/dyno shaft. But I only work on small engines so that task is alot easier for my setup.

[86rocco]

On my buddy's dyno, the weak link seems to be the U-joint, we've broken a few of those. We've never hurt a motor on the dyno, at least not in a manner suggestive of a design flaw with the dyno.

[DaveMcLain]

There are guys who run their dyno by using a hub on the back of the crankshaft that fits whatever spline they are using. I don't do that, I use a drive plate from Innovation Engineering, it's aluminum drilled for every imaginable bolt pattern with a spring loaded hub in the center like a clutch disk. They will make them with any spline you need in the center. Superflow dynos usually use the old Ford input shaft. Mine uses the Chevy/Saganaw style.

The DTS dyno uses a driveplate too. In my case on the engine end, I use a flexplate. I then install a pilot bushing into the crankshaft for alighnment. Then I install the driveplate, I bolt it to the flexplate using 3 3/8 bolts. In my setup I use 2 washers under each bolt for a Chevy and 3 for a Ford(Ford flexplates drilled to same pattern as used on Chevy). I need the flexplate for a starter hookup. You won't need that if you move the starter to the absorber(not a bad idea).

When I first got started with the dyno I used a clutch and an aluminum flywheel. This worked ok but I was dealing with low horsepower(under 400 under 7000rpm) stuff. One time I tested a 454 Chevy that was making around 450 horsepower. Everything went fine but when I finished testing and took the clutch off the back the flywheel and pressure plate where shinny. I switched to a driveplate after that with the understanding that a clutch is not designed to hold an engine that's not accelerating it takes a LOT of clutch to do that so it would slip. It's much safer to get rid of all that weight slinging around too.

[RRBD]

Thanks for the input guy's. The Lord coupler looks like a nice piece, but also looks very expensive. In a previous life, I designed something similar to a motorcycles Cush Drive that was used on a very large Horizontal Boring Mill, It worked very well and may be a cheaper alternative.

How do you guys feel about using an automatic transmission flexplate close to the absorber for starting engines?

[DaveMcLain]

I tried to post this the other day but it didn't take for some reason: A flexplate tends to not be super rigid. In my situation it works ok but it's bolted to the dyno drive plate and that tends to add some rigidity. Keep this in mind because if the plate isn't bolted to something it tends to flex when the engine cranks, if it kicks back for some reason it can knock off teeth in a hurry.