Balance an engine at home?????

[Anonymous]

Ok the shop said it will cost several hundred to balance the lower end on my engine. Since the inline six is a naturally balanced engine to begin with, I think that money could be better spent on something else. But it got me thinking if I found an accurate digital scale (not sure where), why couldn't I weigh the rods, piston, and caps one at a time and use a die grinder to take a little off each until they all match.

Has anyone done this before or have I been spending too much time sniffing fumes in my garage????

 

[addo]

You can static balance, but the spin balance needs to be done on a balancing machine. One of the more frightening possibilities with a badly out-of-balance rotating mass is the flexplate/flywheel bolts coming loose.

Get a dope dealer's scale (a small digital scale in hundredth grams) and work on your rods and pistons with the Dremel and power file; when you're done balancing and polishing the rods get them shotpeened for safety.

 

[Anonymous]

Cool! That is what I was thinking. Too bad I moved to a better area. Where I used to live I could have asked one of the dope dealers down the street ot borrow his scale!

 

[Ronn]

Yep, as he said..I second that.

But are you sure those were "fumes" you been breathing :roll:

 

[addo]

I realise you might be a bit green at this, but soon enough you'll be smokin' em.

...Is there a 7-11 around here? I'm kind of hungry...

:roll:

Do give some thought to the spin balance, even if it's a "quickie". Just for safety's sake. They use "bobweights" which are shot-filled canisters exactly half your reciprocating weight (from memory) on each throw's journal. So you arriving with the weights recorded will save them setup time.

 

[gtm1086]

You also might try contacting a couple different machine shops. I got a quote of only $150 to balance the bottom end.

 

[Anonymous]

I could see possibly balancing the rods this way but I've seen them balance cranks and if you have never done it before forget it.

What if you need to add weight? I mean if you have 5 rods all really close to each other but heaveir then one rod are you going to grind down 5 rods instead of add a bit of weight to one? How do you plan on dealing with the crank? They drill holes in the crank and fill with different types of metal to add or reduce weight when balancing.

Balancing an engine is something I would consider a must if you are trying to make a race motor out of that six. If that motor is going to spend most of it's time @ 7 grand then just pay the extra money to have it done right. If this car is mostly going to be a weekend crusier and daily driver with the occasional burst of speed for fun here and there I wouldn't even have it balanced. It's not needed.

 

[66200i6]

Finding a reputable shop to balance is the way to go. I have looked into this myself. It isn’t as simple as weighing and grinding. The rod needs to be held in a certain position when weighing and that position is rotated and weighed again. Also, if you decide to try, be concerned with how you grind on the rod parts. The grinding needs to be completed with following the grain of the part, which is usually along the length of the rod. I still haven’t read if the grain changes at the cap end of the rod and/or which direction it changes to.

I agree you need to look at how your new engine will be used. You and your pocket book will be much happier when your finally cruz’en.

If I remember correctly the stock rods on these in-lines are forged so you’re going to want to keep them for your rebuild.

Let us know how things progress, Ric.

 

[alloydave]

Get the whole thing balanced from the clutch,flywheel /or flexplate thru to the front pulley.Get these done all at the same time for a complete balance. Cost was $200 nz when i had mine done nearly 2 years ago.
Go with Addo's advice on getting your rods shot peened $100 nz ,and get some arp rod bolts while your at it.

cheers Dave

 

[addo]

Watch for the pop-unders. Pretty much your regular issue static balance process for rods and pistons.

http://www.diynetwork.com/diy/ar_replic ... 92,00.html

 

[mugsy]

I did a home balance myself, and so far it seems to have worked. I have less than 1 hour operation time on the engine, but she is smooth and runs great. Here is what I did and found out.

I work at an R&D facility, so they have a bunch of real accurate scales. I found one the went to 4 places past the decimal on the gram scale. Now there is no way I wanted to spend the time getting that accurate. But the moral of the story is that you need to "select" a tolerance and stick with it.

First, I weighed the pistons with the rings installed amd the pin just laying on top.

Second, I balanced the rods "end to end". I did not just weigh the overall weight of the rods but each end (sorta). I weighed the rod with cap, bolts and the bearings installed. I rigged a way to hang the rod so that the large end was on the scale, and the small end on a support. I found out that the exact POSITION of the small end on the hanger made a huge difference as to the "weight" on the scale. I actually rigged a stand with a 3/4" PVC elbow to hold the rod where the pin goes. The rod should be as level as possible too. I dicovered that the weight was only accurate to the tenth of a gram, or one place past the decimal. The rods in my engine didn't have a pad on the cap but a groove. I still ground the metal out here.

After the big end has been weight balanced I tried the small end. But I found that where the rod pivots ont he sand made a huge difference to the weight shown on the scale. The crank bearing is so large I couldn't find a repeatable way to hang the rod. So this is when I then just did the over all weight of the rod/cap/bolt/bearing and removed any metal from the top of the rod. I made the assumption that if the big end was balanced then just using the overall weight would make the small end in balance.

I used Livernois Speed Shop to balance the crank. They said that with the six they didn't need a "bob" weight.

Hope this helps.