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Old 01-29-2006, 10:48 AM
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Starting Engine on stand-Flexplate or Flywheel?

Gents, we are ready to test fire my rebuilt Chev 350. We are doing this on a stand. We have some debate as to whether it is safe to fire it with only the flexplate attached. Some say absolutely not! Use a flywheel! Some say go ahead, it's fine.
Could you guys help us with this Q?
Better yet, could anyone provide us with a link or comprehensive info about the do's and dont's of running an engine on a stand?

It's a first rebuild for me, and we're pretty sure we've got everything else right, so I'd really rather not screw it up at this point

Thx
Rick

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Old 01-29-2006, 11:58 AM
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i just finished building a engine run stand , i'm using a flex plate and have had no problem. BTW , thanks to doc vette and everyone else who replied to my "how to " thread
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Old 01-29-2006, 12:14 PM
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I would have said to put the convertor on for counterweight ... but apparently it's OK without it.

I would also hope that this "stand" would be something substantial ... like the one in Jeff's picture, and not just a $75 tripod stand. Safety is #1, right?
Be careful when "torquing" the engine.

The other thing is ... do you intend to run this for quite a while, or is this just a "test-firing"? My thoughts are that extended idling / run times with no load may not be a good thing from a break-in perspective. I was taught to vary engine speeds and loads a lot for about the first 500 miles ... and to "stay out of it" until things had a chance to loosen up a bit. (That was hard to do ... couldn't wait to mash that throttle!)
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Old 01-29-2006, 06:49 PM
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we have a test stand and we just use a flex plate. Been using it for a long time with no problems.
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Old 01-29-2006, 07:00 PM
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Quote:
Originally Posted by 66GMC
I would have said to put the convertor on for counterweight ... but apparently it's OK without it.
I must disagree with that. I would not put a torque convertor on it unless the rest of the transmission was hooked up. Torque convertors are quite heavy and need the support of the bearing in the pump. You could risk cracking the flexplate to run an engine with an unsupported torque convertor bolted to the flexplate.
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Old 01-30-2006, 07:49 PM
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And as someone else said, DON'T try this on a simple engine work stand! Tried that once when I was a kid. You should have seen the garage afterwards!
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Old 01-30-2006, 08:04 PM
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Thanks all,

R
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Old 01-30-2006, 09:19 PM
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A flexplate is OK, it's done all the time, just don't rev the engine to 7 grand. Do not put a torque converter on the flexplate. As pointed out, the torque converter needs the support of the front pump in the transmission.

Vince
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Old 01-31-2006, 08:25 AM
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OK guys, I stand corrected on the TQ.

However ... assuming thet the TQ & flex plate are properly balanced ... doesn't that "heavyness" of the convertor (need for support) become less of a factor once you get it spinning?

I'm thinking in terms of: "Centrifugal Force", "Gyroscopic", and "Wheel on a Bicycle"

Yeah ... I know ... you still need the "support" to make sure it runs true. I'd also hate to see the carnage if it ever DID let loose spinning at 6 grand ... so I'm sure you were right to say it was a bad idea.

I've never fired an engine up on a stand, ever.

I did fire a 351C up sitting on the ground, though ... with the trans attached. I also attached a length of chain to the LH side of the engine and tied the other end around a nearby tree. Sparked her up with NO exhaust manifolds ... sweeet. I could tell right away that the neighbors were enjoying it too
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Old 01-31-2006, 08:41 AM
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stand

I run every engine i build on my test stand. I personally prefer to use a flywheel when ever i can... I just don't care for the sound the flexplate makes when using it with nothing bolted to it... i would see nothing wrong with bolting a converter to the flex plate because it is supported in the crank pilot by the diameter on the snout of the converter,,, however there is a big problem with all the fluid that will come flying out of the end if you do not block it off somehow....That is why i don't do it.. I have used flexplates on engines that i do not have flywheels for and i have had zero issues with them....

Keith
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Old 02-01-2006, 07:23 AM
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The "ears" on the pump are connected to the main converter body so the pump turns with the flex plate. It pumps fluid as long as the engine is turning. The inner torus (I think that's what you call the thing!) is free floating. It will move around inside the converter if no trans is installed. So it would sling to one side and cause an imbalance. Running for a short period with just the flexplate is fine. If you plan on breaking in the cam on the stand find a flywheel. You can probably do it just fine with a flexplate, but a flywheel would be better.
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Old 02-03-2006, 12:46 PM
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You don't need either one.

None of my dirt cars have clutches that bolt to the engine. Non but one has a flexplate and it's only 5" across. I like using the coupler. It solid mounts the tranmission the the crank shaft. It's about 5 inches across and bolt's to the crank flange and the inside is splined to fit to the trans input shaft. Just remember without the rotating weight your throttle response will be greater than with a 40 or 50 pound convertor or flywheel.

The trans are set up so the clutches are internal in the trans. They are only about 4" clutch discs. After you get up to speed you shift a lever that disenges the clutch pack(high gear) and you have a solid connection to the rear tires. NO gears or convertor or clutch or flywheel,(ughhh...rotating weight).
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Old 02-03-2006, 01:29 PM
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you really dont want a converter spinning without the imput shaft. the inner parts will self destruct as they are supported by the imput shaft. a good tests stand is an old camaro clip. you can fire it with the trans.

Last edited by shine; 02-03-2006 at 02:22 PM.
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Old 02-03-2006, 02:03 PM
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johnsongrass1, that's fine for a dirt car, but you need something for the starter to engage on a test stand -- hence a flywheel of flexplate. But I do have a question for you -- without a flywheel or flex plate carrying a ring gear, how do you start the engine with that in/out clutch and coupler? Push start only?
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Old 02-03-2006, 04:02 PM
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Unless you like pushing....

Seriously, dirt cars do have flywheels per say. But they are not reguler size. They are very small(5" across or so) and they do nothing but start the car.

Some are mandated by rules to have a clutch inside the bell. Some small triple disk clutches are designed so you use a automatic trans flexplate. these are so fragile that loading the car on to a trailer will smoke the clutch.

Sprint cars have in/outboxes. Most dirt cars have a Bert or Brinn type internal clutch. You get these rolling by pushing ther pedel down, then after the car is rolling at idle speed, shift to high gear which locks the engine and trans and driveshaft together. Let off the clutch pedel.

My point was that either one is just dandy. Your engine doesn't know the differance. There are no reliabilty issues to consider.

You do need a way to start the engine though.
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