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Old 09-13-2017, 11:49 AM   #1
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So I just finished installing my new engine and the first one I've ever built myself. I have Manley forged rods and supertech pistons. I had my crank polished and balanced but didn't have my rods balanced as they were very close out of the box. I have the car running now and running well except there is much more vibrations when I rev the motor than when stock. I haven't put it back up on jack stands to look for anything loose or overlooked but after researching a bit I'm a little concerned I caused this by not balancing my rods. Thoughts?... I'm not opposed to pulling the motor again and tearing the motor apart but would rather not if not needed. Thanks in advance.
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Old 09-13-2017, 11:51 AM   #2
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There are dozens of people here with built engines who never balanced any part of it. My guess would be something else is wrong or got messed up.
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Old 09-13-2017, 12:20 PM   #3
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or you also installed mazdaspeed engine mounts?
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Old 09-13-2017, 12:20 PM   #4
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I have never had any shops completely balance my motors. Never had an issue due to that.
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Old 09-13-2017, 02:00 PM   #5
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Quote:
Originally Posted by Paulryan View Post
I had my crank polished and balanced but didn't have my rods balanced as they were very close out of the box. I have the car running now and running well except there is much more vibrations when I rev the motor than when stock. I haven't put it back up on jack stands to look for anything loose or overlooked but after researching a bit I'm a little concerned I caused this by not balancing my rods. Thoughts?
Cranks are balanced to a calculated "bob weight" which is derived by weighing the reciprocating mass. The rod (with bolts), piston, pin, pin retainers, and rings are part of this calculation.
If the machine shop did not have your parts the crankshaft could only be balanced to what ever the "standard" for the original parts was. It is not balanced to the new parts. If this was the case I'd change machine shops.
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The above is complete BS regarding inline engines; I have built FAR too many V8s recently.
Sorry, I will try to not spread incorrect information in the future...
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If they had everything (and they should have demanded everything that touched the crank including balancer and clutch stuff) you're fine.
All the brand name stuff are damn close to each other (+/- 2 grams is common) and you will have more than 5 grams of oil riding on these parts during operation. Super fine balancing is a waste of time and money IMO.
Balancing makes for a smoother motor but it is not a requirement. Unbalanced stuff works fine.

If you can feel the vibration by just reving the motor up I'd look for loose stuff. Harmonic balancer, flywheel, clutch would be my first suspects...

Last edited by technicalninja; 09-14-2017 at 11:23 AM. Reason: Stupidity, plain and simple
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Old 09-13-2017, 02:08 PM   #6
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Cranks are balanced to a calculated "bob weight" which is derived by weighing the reciprocating mass. The rod (with bolts), piston, pin, pin retainers, and rings are part of this calculation.
If the machine shop did not have your parts the crankshaft could only be balanced to what ever the "standard" for the original parts was. It is not balanced to the new parts. If this was the case I'd change machine shops.
Pertains to 90 degree crank V8's. Has nothing to do with in-line 4's.
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Old 09-13-2017, 03:30 PM   #7
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Yep, Ive heard that if a shop tries to bob weight an inline 4, grab you stuff and run away.
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Old 09-13-2017, 06:59 PM   #8
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Thanks for the replies everyone. Makes me feel better hearing from you that most likely I should be ok. Im going to assume my problem is elsewhere since its only when I rev it up. I should know more after i get under it tonight and check everything out. I did have a hard time installing my ATI Super Damper so hoping that isnt the problem area. While running it appears to rotate smooth. Fingers crossed its something that doesnt require pulling the motor again.
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Old 09-13-2017, 07:30 PM   #9
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ATI pro tip, heat it in the oven for about 10-15 minutes @ 250F, apply Moly Lube -aka cv grease. it will go on 1/2 way by hand then slide the rest with proper tools. easy.
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Old 09-13-2017, 08:25 PM   #10
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[QUOTE=ryansmoneypit;1439409]ATI pro tip, heat it in the oven for about 10-15 minutes @ 250F, apply Moly Lube -aka cv grease. it will go on 1/2 way by hand then slide the rest with proper tools. easy.[/QUOTE

Pretty much what I did the second time except I didnt heat it up. I wanted to but the wife saw me turning the oven on with car parts in my hand and I got the look and took the hint real fast that wasnt gonna happen. Greased it up and ran it in with my old crank bolt. Bottomed out nicely so I would be surprised if that was causing any of my vibration. I just spent about 30 minutes under the car and everything is tight and installed correctly. I was really hoping to find something obvious but unfortunately that wasnt the case.
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Old 09-13-2017, 09:49 PM   #11
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Quote:
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or you also installed mazdaspeed engine mounts?
This may have been a joke, but did you check your motor mounts?
They tear with a sideways glance.
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Old 09-13-2017, 10:14 PM   #12
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This may have been a joke, but did you check your motor mounts?
They tear with a sideways glance.
I installed new OEM mounts when I had the motor out. I just double checked them and they are tight.

I just came in from the garage and while the car was up on jack stands I started it and got underneath it. I hear strange sounds coming from the damper area or the water pump pulley. Could also be my new covers rubbing on the idler pulley.

Honestly it seems to be quieting down and not vibrating as much when I rev it. I very well might be paranoid and over reacting since I've put about 3 miles on it since dropping it in. I took it out and did the flyin Miata break in recommendations and haven't been out since. Maybe this is normal engine break in things? It's all new to me.
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Old 09-14-2017, 12:46 AM   #13
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I'd try your old damper. Did you install a different flywheel? I assume it's vibrating in neutral? Remember installing the thrust washers? Did you plastigage the bearings?
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Old 09-14-2017, 01:11 AM   #14
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I'd try your old damper. Did you install a different flywheel? I assume it's vibrating in neutral? Remember installing the thrust washers? Did you plastigage the bearings?
I'm ready to rule out the damper only because it seems to spin perfectly without any noticeable deflection.
Same flywheel
yes to nueatral
thrust washers in
plastigauged everything and everything was well within specs.
Tomorrow I'm going to try about a few more miles on it after loosening my PPF bolts and making sure everything is lined up correctly to rule out some type of misalignment in the drive line and see what happens.
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Old 09-14-2017, 01:21 AM   #15
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If it's a neutral thing, PPF shouldn't matter, but there is an adjustment spec to the transmission height that affects the driveshaft angle.

Dumb question, but you're letting it get good and warm first? Your slugs should have more clearance than the cast stockers. You might be noticing? I thought the Supertechs were supposed at cold slop.
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Old 09-14-2017, 09:42 AM   #16
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Pertains to 90 degree crank V8's. Has nothing to do with in-line 4's.
Noob asking why. Are most inline 4's a symmetrical crank shaft? Is it because there are equal amounts of mass moving in the same direction at equal distances from the center of mass of the crank. Are 90 degree cranks asymmetrical therefore requiring bob weights?
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Old 09-14-2017, 09:51 AM   #17
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If it vibrates with the car not moving then ignore the PPF and pay attention to the engine, flywheel, and other rotating components there. Imbalanced components that generate enough vibration to easily feel them will destroy the main bearings in short order.

Figuring it out shouldn't involve hoping it goes away.

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Old 09-14-2017, 11:58 AM   #18
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Regarding the ATI Damper- without heating the damper, you are making things really tough on yourself. It is also kind of a No-No to use the crank bolt to drive the pulley on. Moly infused grease is a MUST. You will 100% damage both the crank and the damper if you use most anything else. As an alternative heat source, I often use a heat gun propped up and blowing through the center of the damper. On a low setting it takes about 10 minutes.
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Old 09-14-2017, 11:59 AM   #19
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Could your vibration be tune related? Or a camshaft off by a tooth? If you installed aftermarket adj cam shives then be suspect as they do not come out of the box anywhere close to oem settings. Don't run it hard until you get it figured out. I cracked an forged crower crank once by taking "just one more lap" when trying to figure out a funny engine vibration... It was the damper coming apart. Good luck.
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Old 09-14-2017, 12:48 PM   #20
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I think im dealing with a flywheel or clutch issue like many of you mentioned. While sitting in the car in neutral if I rev the engine I feel most of the vibrations around the tunnel area. When I stand outside the car and rev up the engine its nice and smooth with no noticable ugly sounds. I can lay my hand on the motor while reving it up and it feels very smooth. Cant imagine what i could have done wrong installing the flywheel as ive done that several times before without any problems but im going to drop the tranny to double check and at least rule that out.

I also have stiffer valve springs so maybe thats causing some valve train noise?

Once the car is warm and idle comes down it sounds normal except for the vibration under accerleration.

Thanks for all the suggestions. I will report back after dropping the transmission and checking to see if I screwed something up in there.
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