Jump to content

Pressure plate/flywheel balancing - Is it worth it?


bbuswell

Recommended Posts

I would like to get the opinion of some of the members in regards to pressure plate/flywheel balancing. I’m replacing the pressure plate on my 39 Plymouth mostly because it’s appears 70 years old and I have the tranny out anyway (T5 adapted). The new pressure plate and cover assembly are NOS and my flywheel looks to be in good condition with a nice smooth surface. I’ve read before how seriously some people balance these flat sixes so I reasoned I should take my flywheel and pressure plate to a machine shop and have them balanced. My dad told me that was crazy, he’s replaced many pressure plate assemblies and always just bolted them on and that was it. He said unless I’m turning 7000 rpm or more that balancing those components is a waste of time and money. I don’t go over 3500 rpm so would I be throwing my money away? I’ve read balancing also aids in lengthening part life but will this make a noticeable difference in this case?

Many thanks, Brett

Link to comment
Share on other sites

Folks,

A lack of balance can get you a DUI even if your head isn't spinning 7000 rpm.

Sorry, I just thought of that while beginning this response.

Anything out of balance will cause vibrations regardless how minute. Those vibrations will create harmonics, and harmonics cause metal fatigue and metal fatigue knocks out of the air the majority of the airliners that crash. We're all in a hobby that's largely 'pay your nickle and take your ride' and balancing isn't free, but neither is rebuilding drive-lines.

Ask your friendly neighborhood metallurgist his opinion of what fatigue can do to metal and then decide if balancing (and to what standards) is right for what you want to do. Or you could just Google metal fatigue and read some of the results.

-Randy

Link to comment
Share on other sites

Folks,

A lack of balance can get you a DUI even if your head isn't spinning 7000 rpm.

Sorry, I just thought of that while beginning this response.

Anything out of balance will cause vibrations regardless how minute. Those vibrations will create harmonics, and harmonics cause metal fatigue and metal fatigue knocks out of the air the majority of the airliners that crash. We're all in a hobby that's largely 'pay your nickle and take your ride' and balancing isn't free, but neither is rebuilding drive-lines.

Ask your friendly neighborhood metallurgist his opinion of what fatigue can do to metal and then decide if balancing (and to what standards) is right for what you want to do. Or you could just Google metal fatigue and read some of the results.

-Randy

I agree with metal fatigue being an issue but most airline crashes are Pilot error.

Have investigated a number of them for the USAF. Here is some stats.

Not in this statistic but bird strikes and FOD add most of your mechanical failures.

http://www.planecrashinfo.com/cause.htm

Link to comment
Share on other sites

I agree with you dad also.

i doubt if Chrysler Corp tookthe time to balance the flywheel and other items that you want to do.

Remember this is not a race car but was a car to travel around 40-50 mile per hour and provide basis transportation for the owner of the car.

I doubt that you are going to be pushing this engine and driveline to the max.

If you are goint to do this then do a total rebuild of the car and make it a Streetrod and box the frame beef up the suspension, put on four wheel disc brakes and big V8 with AC and all the gissmo and then you will have a 35K car that can handle the 75 mph speeds.

Restore the car to your liking but decide what you are going to use the car for.

As others have stated use the money for someother part of the restoration and enjoy the slower pace in life. We are all moving to fast in our daily lives. I enjoy driving my 39 Desoto around 50 mph and let the fast people pass me by. I eventually catch them sometime down the road.

This is just my personal opinion.

Rich Hartung

Link to comment
Share on other sites

I agree with you dad also.

i doubt if Chrysler Corp took the time to balance the flywheel and other items that you want to do. ...snip...

I know that the flywheel on my car has drill holes from the factory that appear to be from a balancing operation. So Chrysler did take the time to balance the flywheel. I don't know if Chrysler balanced the flywheel and clutch pressure plate as an assembly.

I marked my pressure plate and flywheel the first time I took them apart and put them back in the same orientation I found them. Not sure if that was necessary or not. Or if it did any good after the rebuilder got done with the pressure plate possibly changing its balance.

I've had my 1933 up to 70 MPH which is about 3650 RPM with its gearing and tire size. Engine and drive train vibration was not a problem. Okay, not really 70 MPH. The GPS was reading 69.9 but I think that is close enough to call it 70.

That same RPM would be about 75 MPH on a P15 with stock gearing and tires. I think most people who are going to push their vintage Plymouths that fast would be using a different rear end and/or overdrive and should thus be running lower RPMs.

So you are probably just fine bolting the pressure plate up and being done with it.

Hmmm. I've just come full circle back to the first reply: "Listen to your Dad."

Link to comment
Share on other sites

Brett, if its just the flywheel/pressure plate you're replacing then balancing just those two again by themselves is not worth the effort, they should have had a cursory "balance" job by the manufacturers, ie Mopar & the Clutch maker..........however if you are in the process of rebuilding the engine, ie, new pistons etc then getting the engine balance by the machine shop is a worthwhile thing, even if its only a bog stock rebuild.............balancing would include the pistons,rods,crank,front pulley/damper & flywheel........anyway thats my 3cents worth..........andyd

Link to comment
Share on other sites

YOu don't have to cut "IF" the presure plat has no groves worn in it.... Just as you wouln't have to cut your drums every time you replace your shoes (unless they where groved)

Now only you can say if it chattered before you took it apart then you might want to at least cut it..

ON my car the most important thing was replacing the piolot shaft bushing made a really smooth operating culuch after the rebuild parts went back in...

DANiel

Link to comment
Share on other sites

I appreciate all of the replies and I think I will spend my money elsewhere and forget the balancing. My flywheel also has balancing holes and the new p/p assembly is the exact same model as the borg/beck unit already in it. I do push my ride pretty hard and have hit a top speed of 93 but I have .76 overdrive and 3.45 rear-end. I usually cruise at 75 mph at 2500 rpm.

Link to comment
Share on other sites

Brett..........93mph?????..........inquiring minds are impressed and want to know more about your 39 plymouth........engine/trans/diff specs......thanks, andyd

Link to comment
Share on other sites

Brett..........93mph?????..........inquiring minds are impressed and want to know more about your 39 plymouth........engine/trans/diff specs......thanks, andyd

I think she had a little more but the front end was getting squirrely. I drive it 25 miles daily on the South Florida turnpike with no hills and straight highway. On the morning commute you need to go about 80 to ride in the fast lane or people will be cussing, cutting off, and flashing their lights. I actually had a whole website about my car but didn't pay the domain fee and it disappeared a couple of years ago. I'm updating it now and will get it back out there eventually. My P7 coupe has a 230ci out of a 1950 dodge mated to a NWC T-5 using a modified Paul Curtis adapter. The rear-end is a 7.6 out of a 94 mustang that original had 2.76 gears with disc brakes. I drove with those gears for a few months and it was surprisingly very drivable. I couldn’t shift into 5th until I was up to 75 or I would start to lose acceleration even at wide-open throttle. I found a used 3.45 Ring and Pinion on eBay for $50 dollars, from an astro van or something. That change made it perfect in my opinion. Also added Charlie Akers front discs and his shock relocation brackets. I'm not positive if the coupe came stock with a front sway bar but my car didn't have one when I bought it. It did have the holes in the frame for one so I found one on ebay for a sedan and that tightened it up even further. I swapped out the original leaf spring hardware and rubber with polyurethane bushing and fabbed up my own shackles. That took all of the body roll out of the rear. The engine has all the standard hop up parts, all of Langdon's stuff, .050 off the head, custom single exhaust. Was thinking around 140 hp. However I just pulled my car a part and sent my cam to Earl Edgerton to get the last few HP I can. Only thing I haven’t done are the high RPM oiling mods. I’ve thought about putting in a rack and pinion from a cavalier on but I think the stock steering is too good to mess with. I did the front-end alignment with a tape measure and some string. I don’t, but I can actually take my hands off the steering wheel at 80 and it will hold a straight line. Any minor vibrations I have actually smooth out at 75 and often forget I’m not in a modern car, and with those big 4 wheel disc brakes I’m more worried about getting rear-end than being able to stop myself. The standard catalog of American cars lists the coupes weight at only 2300 lbs. If anyone wants any further info just ask. Brett

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.

Terms of Use