Well,

I swapped in a RAM clutch conversion kit and the vibration is worse than it used to be.

Not really sure what else to do at this point. I'm at a loss.

 

We agreed, so did you actually change the flywheel?

Did you get the kit with the new flywheel or are you still using the original DMF? Did you put the balance weights on it?

 

I had the same issue when I bought my 1990 Z51 a few years ago. I chased every option only to find the Fidanza SMF that came in the car was off balance. I had to have the crank balanced when I did my engine rebuild so they took a healthy weight out of the rear counter weight. Now the vibration is gone.

 

Hey AZ,

yes I bought the entire conversion kit that came with the new throw out bearing setup, flywheel, pressure plate, and clutch.

They said the flywheel was balanced to LT1 spec and the pressure plate to zero and that I didn't need to do anything but install. It appears that was incorrect.

So yeah I removed the DMF and swapped in the billet steel SMF.

I didn't put any weights on it and wasn't aware that was a thing I needed to do. My gosh their instructions were terrible, btw. Man if you know what to do to fix this, I'm all ears. This emoji sums up what I'm feeling at this point lol

 

Yeah it should have been properly balanced then... don't know what to tell you. Not sure which flywheel you got (steel or billet steel or aluminum), but most of them are externally balanced via cast in weight or machined out outer rings. I think the Aluminum one has bolt on weights, the SPEC and Fidanze ones have bolt on weights. I have a McLoud steel flywheel now and it has the provisions for the weights and interestilgly I had to loctite a bolt into one of the mount holes there to balance it.

About 25 years ago, I got a new drive shaft for a Mustang that caused some vibrations, and so i "redneck" balanced it myself. Got the car on the lift, and took it up to 5th gear at speed and observed the vibration, placed some test weights on the front end of the drive shaft, rotated weights to achieve the smoothest condition, repeated on the rear, and JB welded the weights on. Worked great, but i can not recommend anything so irresponsible. If someone had an old smog dyno perhaps where you can take it up to speed and try some things.

Forgive me if I have asked already or can't recall the story, with all of the recent threads on the topic, when did it start having a bad vibration? After some sort of maintenance? Was the engine ever rebuilt in a high performance manner meaning possibly zero balanced? Not sure how the engine can loose balance, perhaps the front balancer, if the rubber bonding is going out like it's happening with the old DMF's.

Let us know if you figure out what the vibration is, we're all just guessing here.

 

It's quite alright, ask away.

It's had this issue since I bought it. This is the one they recommended. https://ramclutches.com/product/90-0810S/

As far as I can tell, it's got a hot cam, but I'm not sure about anything else. I wish there was an easy way to find out!

So if it was internally balanced with a different drive shaft would that mean I would need a zero balanced flywheel instead? I kinda wish I had one so I could try it.

I inspected the dampener visually and marked it and it seemed ok. I got a SD anyway and going to install it in there in case I missed anything.

The guessing has been driving me nuts haha. Not only that, my most recent guess cost me $1500 and it made it worse 😭 😂 I guess I have to laugh about it though. It was a learning experience. There are no Corvette mechanics in my area that could take a look at it either, unfortunately. The nearest is in Austin and their labor rate is $200/hr which I think is a bit steep.

I'm a mechanic, but I haven't really worked on externally balanced engines like this and haven't ever owned a standard transmission car either. Everything I've done is auto.

I will keep posting with findings. Just trying to figure out how to approach it now that I've made thisnmajor change. I kinda wish I could return the clutch kit, but I doubt they'd take it back.

 

Is the flywheel for ‘87 up not zero balanced? I thought that all of these cars with one piece rear main seals had internal engine balance and zero balance flywheels. Someone else please chime in and back up or refute this. It’s been a while since I studied this.

 

I keep reading that they're externally balanced, but I can't say from any expertise of my own if that's the case.

I'm used to regular old small blocks, lol. I believe even my L31 in my sierra is internally balanced. That thing is smooth as butter.

I was curious though. Apart from taking the pan off, is there any way to verify that?

Like right now, I'm in the process of putting an ATI dampener on there. Once I have the hub off, do you think I'd be able to tell if it was an aftermarket crank?

 

From what the literature says they are internally balance up front and externally in rhe back.

 

Correct. The SBCs with one-piece rear main seals - both L98 and LT1/4 - have external balance via the flywheel. The earlier SBCs with two-piece seals have neutral-balanced flywheels and all the balancing in internal to the crank. I don't know why. Most aftermarket flywheels have a bolt-on weight that can be used or not. Any chance yours came with that weight uninstalled and you still have it? If so, you may be able to open the access plate and bolt it on.

If this engine has ever had a different/aftermarket crank installed, it's also possible that it was changed to a fully-internal balance. If that's the case, then you would need to remove any detachable counterweight from the flywheel. This was how my 396 LT4 was setup, despite the much longer stroke. It often depends on the piston/pin/rod weights (mine had custom and lightweight JE pistons). So my car needed a neutral-balanced flywheel. I don't know any good way for you to determine if that's the case on your engine, short of removing any bolt-on weights from the flywheel and then testing it.

 

Thanks for the reply brother.

I spoke with zf doc about this and he's pretty certain it's not an internally balanced crank. The flywheel I got was externally balanced to LT1 spec by RAM and the unbalance is only really felt at 3k and above, before the clutch work, only at 3k. Zfdoc told me my fillings would be popping out at all rpms ranges if the crank was internally balanced with an attached mismatched flywheel, lol. Seems to make sense.

The new flywheel did not come with any way to modify it with any weights unfortunately.

As an update though, I started digging into my harmonic dampener to swap in an ATI and discovered that one of the dampener bolts was loose. Once I get everything back together, I'll let you guys know how it runs. That likely was contributing to the vibration. The other possibility was that it vibrated loose BECAUSE of the vibration 😂

I'm kinda bummed though because I really would've liked to swap in a Petris setup at this point, but I don't have the extra cash for that. I'm just getting a Murray water pump from O'Reilly's and praying the opti is ok. Gonna do an inspection on it tonight, time permitting. If you guys have any advice on what to look at apart from regular distributor stuff, please let me know!

I appreciate y'all.

 

Very sad to read thru all your struggles on this! Not to mention the time & money that's been spent. I'm hopeful that the front balancer will resolve this for you. May well have been the issue all along! Lock-Tite those bolts!! These factory DMF's are great for their original purpose of smoothing out the driving experience and quieting the ZF box at idle & low rpm rattle. Otherwise, they're an overly heavy and complex device, that is great, until it isn't. If they get wobbly or out of spec, they aren't serviceable. Maybe they could be by the pro's, but the parts aren't even available. In the long run your better off with the new setup you have 👍
In the sad case that your imbalance still exists after the new harmonic is installed, maybe take a look at your spark plugs🤔 a slightly weak cylinder, caused by a variety of things, can give the effect of an unbalanced engine. If it's slight enough that the ecm isn't catching it, it could present further up in the revs as cyl pressure rises, but not as much at idle. A partially wiped exhaust lobe on a cam can do this. if this is the case, the plugs will lead you to the cyl in trouble. Same goes for out of spec fuel injectors. Ohm them out, at operating temp preferably. If it does turn out to still be a balance issue, try to minimize driving it much, or keep the revs low. Severe imbalance is very hard on main bearings. Good Luck with it 🍻

 

I appreciate the info, brother. I will check out spark plugs and injectors if this persists after this job is done. May check the plugs early on anyway because I'm getting a new set of wires already too. They appear to be original.

In terms of the opti, what should I look for when opening it up? What are carbon tracks and how can you fix them? Sorry for the ignorance, but this setup is kinda new to me. Is the carbon something you can just clean up with some fine scotchbrite?

 

One of the 1st things to go on GM's performance builds for these cars, every time, was that flywheel. I can't find the quote right now, but Killebrew despised having to use these flywheels on the Challenge cars. Made shifting & rev-matching much slower. Apparently they held up well, just heavy. This was from an article on the Snake Skinner build:

 

Original wires on your LT4 will be RED. How many miles on your car? I don't think we saw that yet? If your Opti isn't oil soaked & low miles, you could reuse the opti and simply replace the "cap" & rotor. Only as a way to save $$. Big job tho, most wouldn't want to do it again later 😕 your call there. Pictures of ignition carbon tracking are everywhere on the internet. A few pics will do you more good than my explanation haha 🍻

 

Honestly, an original opti is better than even a Petris replacement. If it's running at all, then the module in it is fine and I would not replace it. I agree with Torqsplit that you could just do the cap and rotor on it. But I kind of doubt that's the issue, TBH.

 

Thanks for the info on the opti guys. Yeah, I still have the red Taylors and they're not tin the greatest condition. The motor has 70k on it now so she's still pretty young.

I've been up in the air about what to do. I still haven't been able to really FULLY inspect the opti, but I can say that so far I did rotate the shaft in the rear of it and it was smooth as butter. Makes me think at the least, the bearings are good. And it was firing, the sensor must be good too. Only thing left is to check inside and see how the contacts have been holding up.

I'll take that advice and look up the carbon tracks. Is that reparable or is it better to just go with a new cap and rotor? If the latter, what brand cap and rotor is reliable that you guys trust ? Based on all the stuff I've read on the opti, I'm afraid that I even touched it, let alone changing anything on it HAHA!

But it is what it is. I'm already into this far enough that I just need to SEND IT! I'm also looking to change all the seals on the timing cover. I admit however that I have my reservations on that as well. The little one for the pump shaft is a little worrisome. At this moment, nothing is really leaking except the packing around the crankshaft position sensor, which is easy enough to change. I managed to find the o-ring at a dealership, AC Delco 219-194.

So, even as I write this I'm thinking what I'm going to do is get a set of O'Reilly brand spark plug wires, the Murray (O'reilly again) water pump, the felpro seal kit, a cap and rotor (whichever y'all suggest) and go to town.

 

You're going all the way ehh?! 😀👍 power to ya! I can't speak about Murray? Not familiar. I'm a big fan of Magnecore products tho! I really like the KV85. Their smaller and probly less expensive options are probly top notch also. For street use anyway. Full out race cars probly go even bigger but I've had a set of kv85 on many different vehicles over the years. Hi energy ignition stuff too. They hold up great 👍 And they're Red! 😁
https://magnecorusa.com/wp-content/u...05/catalog.pdf

 

From their catalog:

They are super old school and down to earth. you just call them directly and place an order over the phone! Crazy stuff haha

 

Not to argue with the ZF Doc but I can say I had the exact same issue as you are describing and it was fixed by having the crank balanced. Having the flywheel balanced should have had the same effect but the shop elected to drill the rear cou ter weight instead of removing the bolt on weight on my Fidanza. I am wondering if the literature saying the crank is balance the same for 1pc L98, LT1 and LT4 is wrong. Maybe 1pc L98 came with the same balance as the 2pc rear cars.