Hi Guys. Thought I'd ask you fine fellas some questions.. I just finiched building my beloved 383 stroker engine last night. I had some minor setbacks during the final assembly with the balancing thing prior to this but that is irellevant (i forgot i had the 400 flexplate and used the rear balancer plate for it anyways ). It's an externally balanced crank from summit, the "cheap " one there. Anyhoo, I bought a 400 balancer for a 75 monte carlo with a 400 engine and also the 400 externally balanced flexplate. My problem is that I still have bad vibrations in the engine. As far as I know I've done everything right with the 400 balancer and 400 flexplate. Does the crank really need to be balanced in a shop to be good? If anyone is interested in the summit part#ers they are TCI-399373 for the flexplate and SES-3-51-05-000 for the crank. I picked up the damper at the local Autozone and I did already doublecheck that it is in fact assymetric as a 400 balancer should be. Any help on this is greatly appreciated, I got a monster in the garage and I can't drive it

Thanks alot,
Peter

As a sidenote I could say the compression is real high in it which I will fix with new heads next week. Could that also cause vibrations at 1000 rpm and up?

 

sure it's not a miss that you think is a vibration? sure the engine is running good?

 

Hey thanks for thew quick reply. It does run perfect at idle, just like a stock. as soon as i give a little gas the vibrations start. Now i do have an outragous com ratio on it, like 12:1 - 13:1. (I used the 305 heads with it and it was supposed to be 10.2:1 comp according to calculations. It sure feels like its a bad balance but I really couldnt tell.. When i road tested it it took off like a rocket but overheater quickly due to the high comp ratio and the lean a/f mixture. Do you know if there was only 1 type of balancer for the 400? Maybe I got the wrong kind?

Thanks again
Peter

 

did you have the rotating assembly balanced? if so, did they balance it with the flexplate or not, if the motor is balanced without the flexplate then putting a unbalanced flexplate on it would make it very unbalanced and vise/versa. with that much compression you probably need to run racing gas only. and I doubt those heads are helping you make any power. you could probably get some stock 350 heads and make more power than your making right now.

 

My 350 had the shakes bad after 1200 rpm when I had the valve lash to tight on a few cylinders. It also got hot easy. Just a thought.

 

valve lash will cause alot of culprits......... the first being an unstable at if it will idle at all...... i'm having to wrestle with mine as i speak......

it sound like it's just alot of cam and that vibration is the thump thump you get with a big cam.....

 

It turns out that I have to get the crank balanced at a shop even AFTER I got the 400 damper and 400 flecplate.... Something It didnt say anything about in the summit catalouge when I bought it a year and a half ago... So now I have to take the new engine out, take the crank and all the other stuff out and spend another 200 on the crank to get it balanced... If I would have known this Id just buy a internally balanced crank in the first place lol

Thanks for all the input and help,

Peter

 

looks like you got it now. the cranks come as a rough weight that way you can run things like 6" rods and domed pistions ect. and not have to add weight. just remove less from the crank

 

I just went through the same problem you're having and posted about it a month ago. I learned out like you that just about all stroker cranks have to be balanced to the rest of your components. My Scat cast crank is probably similar to the one you have from Summit. Don't feel too bad though about pulling the motor again, you're not the only one who's learned the hard way. Oh, by the way, my crank had about 290 grams of weight removed on one end and about 340 grams taken out on the other. No wonder it about shook my teeth out.

 

Hi Joe. When I got the crank back a few days ago they told me it was 220 grams off in the front and 180 in the back. I'm hoping to start putting it back together this weekend. There's an awesome machineshop in the back of the Napa store here in Brownsburg that helped me out once I started asking them stuff

What part of town you live in?

Peter