1976 360 engine swap

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Farmall1938

318 poly owner
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Hey all- Continuing the saga of fitting a 360 into my original poly 318 dumptruck....... I got a 318 flywheel, and modified it per the drawings someone emailed me...... but it was a 130 tooth, and my bell is for a 143 tooth......so needless to say, the starter didn't mesh. Got another 318 flywheel, nice shape- it's the larger 143 tooth. Starter meshes fine. I modified it to 360 specs re: the drawings...... Got it installed today, and fired up the engine for the first time. There is a vibration. Can anyone tell me why ???? Any ideas what to do to rectify the problem ???? I followed the plans to a tee- 3 holes to the right depth, exactly to the specs of the layout..... I don't get it.

10.5/11........130/143.......internal/external
Dang mopars anyway !!!!!

Ryan
 
I don't have a clue what it could be but it isn't a Mopar only issue with the internal/external balance. Chevrolet has the same thing with 350/400 and the 396/454.
It was a pretty common Detroit practice.

Chuck
 
Any idea WHAT detroit was thinking of when they started this STUPID idea in the first place ????

Engineer #1 "Hey I got an idea ! Lets take a balanced flywheel, and drill a bunch of holes in it. Then lets make the crankshaft out-of-balance to match the flywheel"

Engineer #2 "Why don't we just leave it the way it's been for 50 years ?"

Engineer #1 "That would make too much sense, and in Detroit, we don't make cents, we make cars !"
 
Well, the drawing you got was for a 130 tooth flywheel. It's a smaller diameter. The 143 would have to have less material removed from the same spots, because the wheel itself is bigger....Menaing the weight is "further out" on a lever, and that cahnges the effective weight. What you need to do, is get the right 360 143 tooth flywheel. I'm sure there is math to figure out the difference, but at this point, how many times do you want to have to install it and see if it's still out because it's not starting from nuetral anymore? You WILL destroy your 360 in VERY short order running it with a vibe of that kind.
 
Farmall1938 said:
Any idea WHAT detroit was thinking of when they started this STUPID idea in the first place ????

Engineer #1 "Hey I got an idea ! Lets take a balanced flywheel, and drill a bunch of holes in it. Then lets make the crankshaft out-of-balance to match the flywheel"

Engineer #2 "Why don't we just leave it the way it's been for 50 years ?"

Engineer #1 "That would make too much sense, and in Detroit, we don't make cents, we make cars !"
Click to expand...
i was always wondering why they did that, and why is the 340 different then the 318 and 360 for balancing, which one is better? is there one that is better, externally or internally :scratch:
 
Farmall1938 said:
Any idea WHAT detroit was thinking of when they started this STUPID idea in the first place ????
Click to expand...

It's all about dollars! They went from forged to cast cranks to save money, cast cranks are lighter than forged so to have acceptable balance, weight would need to be added. Mallory metal is very expensive plus it adds extra operations that also add cost.

Since a cast crank motor with external balance is more than adequate for the purpose that is how we get to where we are. Remember, Detroit does not design cars for the 1/2% of folks that want to do engine swaps or do other hot rodding activities.

Virtually everything we touch is a compromise between cost, function and reliability. Any engineer worth his salary is looking to remove cost without impacting function or reliability. Since an extrernally balanced motor does not impact fuction or reliability for a daily driven vehicle but can make a very significant reduction in cost it was absolutely the right decision to be made.

Having been an engineer for the past 32 years I am faced every day with how best to make the compromises for the target market. Many times those choices are not what I would make if I was designing a product for myself but my job and salary depends on providing a product that the largest number of people want to purchase.
 
Did you use the correct 360 harmonic balancer also? The 360 harmonic is also balanced for the engine. If you put a harmonic from a 318 on there I would have no doubt about where your vibration is coming from.
 
moper said:
Well, the drawing you got was for a 130 tooth flywheel. It's a smaller diameter. The 143 would have to have less material removed from the same spots, because the wheel itself is bigger....Menaing the weight is "further out" on a lever, and that cahnges the effective weight. What you need to do, is get the right 360 143 tooth flywheel. I'm sure there is math to figure out the difference, but at this point, how many times do you want to have to install it and see if it's still out because it's not starting from nuetral anymore? You WILL destroy your 360 in VERY short order running it with a vibe of that kind.
Click to expand...

I thought of that same thing and if he drilled the holes using the off of center measurement then he should be OK because what he has left out side of that measurement should be neutral, but you are right if he drilled the holes measuring from the outside of the fly wheel it will definately have a different balance because the weight was removed from a different radius from the 130 tooth wheel.

Chuck
 
Please understand I have seen the drawings, but never done it myself..so i'm just tossing this out there too. But, that being said, even measuring out from the center...he's going further out if it's removed from the outer edge. (I dont know if it is, but my 360 flywheel has a 1/2 moon out of one edge) The amount of material to remove depends on the distance from center, and if you remove it from a larger diameter edge, you should be removing less material. Because the same volume removed from a longer distance away from center will carry more mass offcenter when rotated. God I hope that makes sense...
 
It does but he is measuring out form the center of the crank so it is the same distance (radius) on both flywheels. For example if the measurement for drilling was 9" from center of the flywheel on the 130 tooth wheel and he used the same 9" from center on the 143 tooth wheel they should be the same balance as long as anything outside of that 9" dimesion is neutral. In other words he is removing the same amount of material in the same spot on the flywheel as measured from the center, but the measurement would be a larger number on the 143 wheel if measured from the outer diameter.


Chuck
 
Heres what I used.... hope it comes thru OK.

360mod.jpg
 
....Another quick question..... Does anyone know the relationship between the flywheel balancing holes, and the balancer weight ? When the balancer weight is facing down, the holes in the flywheel are almost straight down as well. I'm confused, because why would you add offset weight to the balancer, but subtract offset weight from the flywheel ????? HELP !!!!
 
Thanks Chuck, I was thinking that the material was removed from an edge. Now it makes sense...lol

Farm, the holes create a heavy spot on the flywheel. the heavy side should be in line witht he counterweight on the rear section of the crank...the alancer's heavy spot should be in line with the front counterweight.
 
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