Guest mattrp Posted August 16, 2000 Share Posted August 16, 2000 Ok, for those of you who like to rest your hand on the shifter, I'm assuming ones attached to the tranny directly, what do you feel as you rev through the rpm range. I just changed my front pulley to reduce vibrations, and it helped, but I still feel what I would liken to the feeling of a lawnmower handle, but just increase the rpms a little. At idle it is smooth, once i hit 3 it becomes pretty intense and then it oscillates in and out, until 5 where it smooths out again. Then on decel it goes in reverse, and kinda shudders for a second as it settles into its idle. I'm at about the point of going to the junk yard and grabbing a harmonic balancer. Am I just being to picky? Isn't a sbc supposed to be glass smooth? Matt 72 500Z Quote Link to comment Share on other sites More sharing options...
Mikelly Posted August 16, 2000 Share Posted August 16, 2000 Matt, Which trans are you using? Also, it sounds like a drive angle issue... Have you checked the pinion angle with a angle finder? You can buy one for about $18 at Sears... Go to Pete's link and read about what can happen and how to fix it... sounds like you are suffering from the same thing every V8 Z suffers on initial build.. But don't sweat it, this is fixable... Read Pete's article and then ask us some more questions! To correct mine, I did the JTR fix by cutting the mustache bar bushings to give the right angle! Mike ------------------ "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
Guest mattrp Posted August 17, 2000 Share Posted August 17, 2000 Mike, I am certain it is not my drive angle, although I am willing to bet that causes some problems, but I am able to produce this vibration with the clutch depressed. It is something completely within the motor. If I sit at a stop, tranny in neutral, or clutch in, and rev, its smooth to 3, then the vibes pick up, peak at 4, then decline to smooth again at 5. On decel it is backwards with a little shudder at about 2, then it settles right in. I have never felt this with any otehr motor I've had, they were always glass smooth. I'm flat out stumped! I will be doing the jtr mod on the mustache bar though, just as soon as I sort out this engine vibe. Thanks for your help Mike. Matt 72 500Z P.S. Mike, your car kicks ass. What type of times are you getting at the 1/4 mile. I'm sure ive seen them, but cant remember. Quote Link to comment Share on other sites More sharing options...
pparaska Posted August 17, 2000 Share Posted August 17, 2000 Matt, what's the history of the engine balance, the flywheel, etc? If you have a 400 crank that's not internally balanced at some shop, you need a flywheel with a counter weight, as well as a harmonic balancer for a 400. Then again, I remember putting a 350 "goodwrench" engine in a truck that had a 350, and it had a vibration that we never traced down. Definitely in the engine and not the trans, etc. Quote Link to comment Share on other sites More sharing options...
Guest mattrp Posted August 17, 2000 Share Posted August 17, 2000 This was a completely stock 305 out of a camaro z28 (84). I am using all original parts except new aluminum crank pulley which helped a lot, and one new rod becuase I spun one rod bearing before the rebuild real bad, and a set of pistons obviously from the rebuild. But the motor shop did a full rebuild, I dont believe they did a balance on the motor, but I assume its not that because this vibration was there before the rebuild. Thus far I have heard from my motor shop guy that it could be a out of balance flywheel, but I cant go with that because the vibration comes in and out again. Is it possible that overtighening the front belt could cause this, or maybe because I am using the top passenger side mounting for the alternator the belt run is too long. I just revved my friends stock 280, and there is absolutely no vibration and this pisses me off to no end. I want a smooth motor. I just hope the harmonic balancer change does the trick, cuz I'm crazy enough about this to pull the entire motor to get that flywheel balanced. I leave for college in four weeks, gotta hurry. Thanks Matt 72 500Z Quote Link to comment Share on other sites More sharing options...
pparaska Posted August 18, 2000 Share Posted August 18, 2000 Matt, are you absolutely sure it is firing on all 8 cylinders? I know this sounds nuts, but if it's a 305 with the stock harmonic dampener and flywheel and all 8 rods and pistons are the same weights, it should be fairly smooth. But if it was vibrating before the rebuild, the only thing I can think of is that the compression is very low in one cylinder, the cam is wiped on the lobes for one cylinder, or there is a bad plug or spark plug wire. How's the compression on all the cylinders? Have you tried running the engine with just one plug wire off (with a plug on that removed wire that has it's case grounded)? Try this with each cylinder. If you find that with the plug wire off a particular cylinder it runs no worse, you've found the bad cylinder. Then test the amount that the valves are opening on that cylinder, relative to the others. If it's lower, you have a wiped cam. Just a few ideas. Quote Link to comment Share on other sites More sharing options...
Guest mattrp Posted August 19, 2000 Share Posted August 19, 2000 Good idea pparaska. I was actually considering checking the wires, although they are relatively new. I cant imagine that the cam is wiped cuz it has 500 miles on it. And I did the valves 3 times over until every time through they came out perfect. You know, start at top dead center, tighten number one to just loose, then extra turn, rotate crank 90 degrees, do the next cylinder in the firing order, repeat 8 times. Hmm, ignition, I'm getting desperate, maybe it is. I yanked the front pulley today and ran with just a balancer, and the vibe is still there. So tomorrow I'm getting a different balancer to try. If that doesnt do it, I'll check the wires. I wish I could check the ignition through the rpms somehow. The distributor is new and the accel coil is new too, but same as from previous rebuild. This is SOOO frieking weird. Smooth to 3.5, vibes till 4.5, smooth. Hmm. Thanks for all your help. I'll keep you posted. Matt 72 500Z Quote Link to comment Share on other sites More sharing options...
pparaska Posted August 19, 2000 Share Posted August 19, 2000 Matt, The fact that it's smooth to 3.5k, vibrates until 4.5k, and then is smooth might still be some kind of engine imbalance. That sounds like a classic "harmonic" vibration - that the engine hits a harmonic frequency (rpm) and vibrates noticably more. It could be that the engine mounting system has a natural frequency that coincides with the vibration in that rpm range. Are all the bolts for the engine mounts and brackets tight? Are the mounts good? ------------------ Pete Paraska - 73 540Z - Marathon Z Project - pparaska@home.com">pparaska@home.com - Quote Link to comment Share on other sites More sharing options...
Guest mattrp Posted August 21, 2000 Share Posted August 21, 2000 I hate to say it pparaska but I think you nailed it with the harmonic vibration thing. I changed the harmonic balancer to new one, and it helped, but it is still there. I think that is just the harmonic frequency of the 1/4" sheet steel (JTR) set back plates and the engine mounts and the tranny mount. I think I may be asking too much from a motor which was not balanced by the shop and is relativley hard mounted. I think I am jsut going to accept this as a fact of life. Maybe next summer I'll drop a new 383 in there. I am going to try tighening all the mounts, and I am going to attempt to dampen the motion of the sheet steel mounts with a belt or some rubber house, just too see if it makes a difference. Thanks again Mike and Pparaska! I'm still wooping the hondas and having some major punch in the seat, so things are all good! Matt 72 500Z Quote Link to comment Share on other sites More sharing options...
Mikelly Posted August 21, 2000 Share Posted August 21, 2000 Matt, I'm suffering from the same thing...a buzzy motor and I think you are right on with the description of the mounts. They do allow a lot of buzz to transmitt into the car. Unfortunatley that is the price to play... Mike ------------------ "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
pparaska Posted August 21, 2000 Share Posted August 21, 2000 Guys, I think the JTR mounts are great, as far as making the setback a bolt in operation. But those 1/4" plates probably are the cause of some of the harmonic vibration issues. There are some V8 Z conversions I've seen/heard about (Henry Costanzo's for one) that use a separate engine crossmember bolted to the frame behind the stock crossmember, that allows for the mounts to bolt directly to it. Henry bought his from someone, but I don't recall his name. I'd bet he's from Georgia. I'll give Henry and email and see if I can find out. Henry's car also has the stock engine mount "towers" cut off and the area cleaned up so that it looks like they were never there. For those of you that are into designing and building parts, I think this would be a great idea. The issue is how do you attach it to the stock Z frame rails? I think a good way would be to have the new crossmember sandwich the rail top and bottom, and through bolt it through the frame, but you would need to install some sort of tubular spacer to allow tightening of the through bolts without crushing the rail. Another option would be a weld in piece, but I'd rather not have it that way. ------------------ Pete Paraska - 73 540Z - Marathon Z Project - pparaska@home.com">pparaska@home.com - Quote Link to comment Share on other sites More sharing options...
Guest Drewz Posted August 21, 2000 Share Posted August 21, 2000 My V8 is mounted via an engine plate I made from 3/8 alum. and I get a little vib. noise but when you custom you sometimes have to give a little to get a lot. A new fluidampner made the vib. almost completely go away I might add. Good luck. ------------------ Drewz Quote Link to comment Share on other sites More sharing options...
Guest mattrp Posted August 21, 2000 Share Posted August 21, 2000 Yeah, I was wondering if a fluid damper would help. It is a little out of the price range right now (kinda funny saying that considering the value of the car). I'm gonna do some experimenting this weekend with some dampening material on those mounts. I think some of the issue is also my stock rubber tranny mount. Hopefully the eurethane one I have wont vibrate as bad as it did before when my balancer and pulley were bad. Maybe it will even help. I'll keep you guys posted. Personally, smooth feels more powerful, so I'm gonna do everything I can to make it that way. Matt 72 500Z Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted August 22, 2000 Share Posted August 22, 2000 I HAVE HEARD NOTHING BUT GOOD THINGS RE FLUID DAMPERS. DO NOT HAVE ONE ON MY Z AS OF YET BUT PLAN TO ON NEXT SET UP. Quote Link to comment Share on other sites More sharing options...
Guest mattrp Posted August 22, 2000 Share Posted August 22, 2000 So much for the eurethane mount feeling smoother. Damn thing vibrates big time. I love the tight feel of the car but it vibrates at all the wrong rpms so I'm gonna switch back. I did set the motor about a 1/4" farther forward on the change though to line up the tranny mount a little better. Maybe the reduction in preload will reduce the rubber mounts transfer to the body! God do I love fiddling! Matt 72 500Z Quote Link to comment Share on other sites More sharing options...
Cyind Posted September 3, 2000 Share Posted September 3, 2000 The one good thing about a 700R4 and B&M Mega Shifter is the Racing cable does not transfer any vibs... LOL ------------------ Z U V8ter http://cyind.com Rspencer@satx.rr.com Quote Link to comment Share on other sites More sharing options...
pparaska Posted September 4, 2000 Share Posted September 4, 2000 BTW, Henry Costanzo got back to me about his V8Z's crossmember. He made it himself. It uses a section of 4" pipe to pass the steering shaft by the motor mount. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.