so, i have been doing a lot of learning in the process of rebuilding my engine. two things i have learned are that the pistons and connecting rods are made of electrically dissimilar metals, and that engine degreaser is an ionic solution.

so in an attempt to remove some coking from the pistons (ring lands, etc) I have corroded holes in the annodized coating of the pistons. :/ It ended up being a $600 mistake, and has cost me lots of time, as I have gone from ready yo install pistons once they are clean, to waiting for pistons to ship and looking for pin bushings. grr.

anyway my question to the forum is: my pistons are all corroded, with some annodization missing. I weighed 4 of them dry, with a quick cleaning, they all weigh within 4g of each other. what are the tolerances for piston weights? how are they matched? can I trust the weights of my other pistons with a little corrosion and missing a little annodization? will my motor a-splode for this reason, or some other, yet to be discovered reason?

also, does anyone want a description and parts photo of a overhaul of the injectors?

thanks
kebbo

I dont know what concoction you've used,but engine degreaser wont harm these pistons.cleaning pistons is easely done by soaking them in water overnight and letting them sundry next day.Most of the carbon will peel right off.to clean the ring lands i use a broke in half piston ring to scrape them clean.

These old pistons are done for.

You can equalize the piston assemblies by weighing the rods,and then both ends seperatly, each piston pin and the pistons. you should be able to mix and match them to within 1 or 2 grams of each other.the bottom of each rod can be ground back to get the same weight there.

my rods are fine. all i am replacing is the pistons, do I need to weigh the whole assembly or just the pistons themselves? also how do i just weigh _one end_ of a rod? the measured weight will change depending on the angle of the rod and where I am supporting the non-weighed side.

and yeah, i dropped pistons and rod assemblies in plain purple engine degreaser. I wish I had known about the bucket o' water trick before I smoked my pistons :(

edit: oh, i get it, if the piston or rod is off a bit, mix and match to make them all equal. but how close to the orig. pistons do they have to be? is it a problem it they all match within 2g but are each 10g lighter than the ones i took out? and i haven't worked out how to weigh part of a rod yet

Stock stuff is usually 8 grams from highest to lowest. Strive for 1 gram.

How to balance a rod: First you balance the big end. Little tricky without the proper equipment. The rod should be held perfectly level with the small end supported by the scale. Same distance and perfectly centered big end as the pivot point. Find the lightest and then grind or polish/sand the small ends of the other 7 to match. Once the big ends are matched you can then balance the complete rod by grinding/sanding off the top. Again find the lightest rod and grind/polish the other 7 rods to match the lightest.

Alternative balance is to find the lightest piston and put i with the heaviest rod. This is sometimes done in engine balancing when the small end of the rod cannot be ground on or the pistons cannot be cut.

Link: http://images.google.com/imgres?imgurl=http://www.eddiesvalvegrinding.com/picts/rod-balance.jpg&imgrefurl=http://www.eddiesvalvegrinding.com/balancing.htm&usg=__ZTz47-ms_-0dcnBCHKCo4dKLgWg=&h=338&w=450&sz=23&hl=en&start=5&tbnid=zxSlR7FqLMb2_M:&tbnh=95&tbnw=127&prev=/images%3Fq%3Dbalancing%2Brod%26gbv%3D2%26hl%3Den

Link: http://www.diynetwork.com/diy/ar_replica_car_kits/article/0,,DIY_13707_2272192,00.html

I have personally probably balanced 1,000 engines. Next; How to over balance.

How long did you let them soak in the bucket/container of Degreaser?
What was in the bucket/container before you used it?
Is the picture in your second post the pistons?
I usualy use a 000 piece of steel wool to help clean any carbon or grunge off after soaking.
The wool is very very fine and will not gouge or scratch the surface.
If the pistons are within spec and there is just a little corrosion just have tthe tops ceramic coated.

@ dieselpro: thanks i'll try that. i"ll have to make one of those suspension rigs. also, where does one find a scale with the appropriate ranges? only thing i could find is a scale from Harobor Freight. it measures up to 7lb in grams or oz, but i have no idea what the accuracy of the instrument is.

@GJF: left them for about a week. because of my job, i am living out of town for a few months and I can get back for one day during the weekends, so i do things like soaks that i think will take a long time over the time I am gone. oops :/ also I thought the pistons were destroyed, so I just ordered new ones. i have no idea what else was weakened or corroded by the process

a harmonic dampener wont help compensate for poorly balanced engine will it? I will definately take the time to balance to the best of my ability, but a little extra insurance would be nice. my stock one is fine, and i'd like to avoid the $450 extra expense to get a fluidampr

if you want to save a few bucks i'll sell you a set from a 93 for cheap, tops look good. send the new ones back.

ALL YOU NEED IS A POSTAL SCALE. Keep in mind everything must be well centered. The "bushings" we used on the big end and small end had bearings. Double check everything before grinding. We used a high speed sander on a rubber flex drum.