TOPIC: Piston weight: Cast-vs-Forged

I have a ‘73ish 1500 L-6 here that needs one .040 Wiseco, and all others will be cast aluminum STD.
I’m waiting to receive the piston from eBay, and am wondering if anyone knows if the forged Wiseco is significantly heavier than a STD cast aluminum piston.
I'm not very excited about putting a forged piston in with cast pistons, but I've found mix-match forged, cast, high dome & low dome pistons in the 99ci L-6 Mercs before that seemingly were working okay together.
If it is heavier,...How would you go about balancing it to match the weight of the others? Where would you remove material?
Fortunately my machinist is up to speed on the specs for boring O.S. for the Wiseco pistons.

I remember "daveswaves" did some balancing of the pistons & rods? – in an EFI L-6 experiment he tinkered with.
What is the latest on that project anyway?

Hopefully he will spot this post and reply.
(I apparently don't have your current email addy Dave)

I purchased a digital scale in the kitchen wares area at Wal-Mart yesterday. It looks like it should work pretty well for balancing pistons, etc.

Hopefully someone can share treasured insight on my dilemma.
doc F

Can of worms here doc! On weight? Forged is denser so heavier. But? Forged are considered higher performance so being made shaved at first of any excess weight possible. Ya really won't know until ya get two to compare. And it shouldn't be more than a few grams, but I'm guessing here. Interesting thread here as curious myself!

I weighed the .040 forged aluminum Wiseco high dome power ported piston and compared it to the weight of a .015 cast aluminum high dome power port piston, both for a 99ci inline-6.
The pistons weigh the very same 13.2 oz,...BUT the wrist pin for the Wiseco is visibly thicker material and weighs 3.1 oz compared to the cast aluminum piston's wrist pin's weight of 2.6 oz.

I need to do more investigating:
What do (3) rings weigh vs (2) rings?
What is the difference in weight between a cast .015 high dome PP
piston vs a cast low dome PP piston?
What is the difference in weight between a cast high dome non-PP
and a cast high dome PP at various sizes (STD, .015, .030) as
these are all commonly mix-n-match combinations found in various
rebuilt 99ci inline-6 Mercs.

"stay tuned",...doc

Lemme see if I can shed some light on this. And all good questions too. On the piston pin being heavier like 14 grams thats gonna toss motor out balance IMO. BUT, what is the pin O.D? Is it the same as the cast? What about just using a stock lighter pin? My take is it has to be as O.D has to be to same the con rod small end, right? I don't think that would be a prob as were not building a screaming race engine here.

Also if you do have to remove weight any, I'll explain what to do to relieve "Stress risers".

This..What do (3) rings weigh vs (2) rings?

If both are similar in "shape" the ring groove material removed for the 3rd ring is simple replaced with the 3rd ring. A 2 ring should weigh the same?

Anyway, WTF is that in the second pic? Is it what I think it is?

I considered that, but my concern with swapping out the wrist pin is based on my uneducated guess that the forged piston's heat expansion rate is different from that of a cast piston, so consequently maybe it needs the thicker wall wrist pin???

I did some more weighing that leaves me wondering just how much it matters in the ancient technology of the inline-6 Merc.
Low Dome, Power Ported, .015 cast aluminum: 13.0 oz
Low Dome, Power Ported, STD cast aluminum: 12.3 oz
High Dome, no P-Port, STD cast aluminum: 12.9 oz
Hi-Dome, no P-Pt, with (2) finger ports, .030 cast aluminum: 13.6 oz
Hi-Dome, Power Ported, STD cast aluminum: 12.5 oz

Having built and run the heck out of many 99ci inline-6 Mercs using various combinations of these cast pistons, I'm left questioning whether or not my current .5 oz weight difference is going to cause any problems.

Opinions?
doc

"Anyway, WTF is that in the second pic?"

The blue devise is a Dynometer, used to create load on outboard engines for testing purposes. The water tub aids in keeping the hydraulic motor's oil cool.
The max horsepower for this unit is about 200.
It eliminates the need to drop the boat in the water to complete testing in most cases.
Pretty cool.

Just what I thought! NICE FIND! What gave it away me was the "padded ears" that would hold it to the the fins L/U. And also ya sure can make a damn bunch bucks "Dyno an OB". Friend mine back east was a Harley engine builder. He bought long ago a M/C Dyno. Stopped building (kinda) and just traveled all biker events with the Dyno in a enclosed trailer. Lotta bucks made simple "having fun" with anothers bike! Ya got a damn nice prize there my friend!

Hi Thom, just saw this message. This email address is being protected from spambots. You need JavaScript enabled to view it..
Funny you ask about the efi inline. It has returned to my shop after almost two years. I melted a couple of pistons on it and traded the who!e mess for a tiller outboard. I just bought it back lol. I too have pulled forged pistons from in lines. I spent a lot of time balancing pistons and rods on that engine. To be honest it is not going to make a difference unless you are spinning really high.
I will be pulling apart the engine and repairing it. I will have another go at writing a fuel map for the efi. I will keep you posted.

First off Thom, this.."I considered that, but my concern with swapping out the wrist pin is based on my uneducated guess that the forged piston's heat expansion rate is different from that of a cast piston, so consequently maybe it needs the thicker wall wrist pin???)"

Good question and I have no answer? Hmmm. Anyway, I'm going to side with Dave here as thinking it a bit and being a inline, I don't see any major problem as like I said before, as Dave..were not building a high RPM endurance race engine. I'd say just go for it. 1/2 oz isn't much (although it sounds like it), and bet on production motors that are not checked for equal weights anyway (I would think) are probably assembled just by grabbing rods and pistons out the box and just shoved it. Probably easy 1/2 oz diff in production motors to begin with as not "blue printed". Heck, I dunno...

Hi all,
So I balanced only one inline, my very first rebuild years ago on a 1500. I was a car nut at the time and balancing was standard procedure on any Perf V8.
Land and Sea was local too me ( famous for their hydraulic jack plates, turbo v6 OBs and switch pitch props, Merc bought the patents on it) and was at the center of performance outboards both inlines and the then recent V-6's. Their opinion was I was wasting my time on a 6000 rpm motor but.....I decided to do it anyways. They showed me where to remove material. Their comment was it would not hurt to have the reciprocating weights similar but the cranks etc. where generally far enough out that they could not balance the rotating assembly anyways.
For the rods I hung them horizontal, one way with big end on scale and the small end hung on a small pin to weigh the big end. Then I reversed so I was weighing the small end. I would then match all the rods to the lightest small and the lightest big ends found.
I set up a router with a small dia grind stone so I could lay the rod on the macined sides and run the rough beam sides against the stone. I smoothed the beams to match weights both ways, and smoothe the tops of the small end an the bottoms of the rod cap, these areas do not take the load of the piston pushing down during power stroke. All bearings and cages where the same.
For the Pistons I massages the skirt up between the pin bosses using a Dremel. I just went for same weight,
All pins and bearings, rings etc. were the same.
I got everything to within a few grams.
Doc in your case it would be the heavy pin I'd be concerned about. Although I'm not a mix and match kind-o- guy I would swap to use a thin wall similar pin, the steel is heavy. From a sizing point of view the O.D.of the pin is tight tolerance sized for the needle bearings/ small end ID so any pin has to be close in size for correct bearing function.
This same goes for the piston they are all sized for that similar tight tolerance OD pin.
You could mix and match pistons and con rods to get similar total weights closer together at least on any given group of two running opposite of each other. Like 12 34 56. That's all I do to minimize crank deflection ( in theory) at the reed cage between each group.
I'll go with Land and Seas assertion that the OBs are pretty bad, they never balanced the in lines they did.
By the way there is a cool vintage video on you tube of them running their Hydrostream Viper with a killer in line 6 shot on a lake in NH.
Randy

Oh the dyne is awesome!!!! Land and Sea had developed one back in the 80's is it one of theirs?
R

Randy,
Thanks for taking the time to share your write-up.
LOTS of interesting insight, and I really appreciate being able to gain knowledge from posts like this.
I don't want to ever stop learning the secrets of the Tower of Power.
I'll probably use a lighter wrist pin in the Wiseco.
I'll probably play with weighing things, and if I find something outlandish, I'll either swap it out or trim it down.
I'm not sure of the origin of the Dynometer.
This is the second one I've had, and really kicked myself for selling the first one. I didn't think I would ever be lucky enough to find another, but I did. This one was recently rebuilt too.
I'll track down the manuals, and share what I find in respects to the manufacturer & related franchises. I had the manuals in my 'hot little hands' a couple days ago, while hunting for something else, so I 'should' be able to locate them again.

doc

Like said me and Randy. I'd go with the light pin and simple say a prayer to the "Merc Gods", and slam it home. I can't really see much if any prob heat expansion piston/pin/small end.

Hey Thom, curious here. Whats the weight diff between a cast stock piston, and cast .40 over?