924Board.org

[peterld]

Hiya Dan, I'm with Bass GT on this one. What you do now will come back in spades to either haunt you or thrill you. All items should be 'blueprinted', ie. all items should be same size, same weight, same cc for pistons, etc. As you are using aftermarket pistons and rods your tolerances should already be very close. There is lots to be gained in the clutch, pressure plate and flywheel area. Skimp now and you may rue your decision.
Just my thoughts. Pete

[ideola]

I'm at the stage of my UWB project build where I need to have the balancing work done for the components that go into the rotating assembly. Here's a list of the components I think I need to take in:

- crank
- rods
- pistons & pins
- flywheel
- pressure plate
- front pulley
- front crank-mounted cam gear

Other related items to consider:

- attachment bolts (for flywheel, pressure plate, ring gear, pully, etc.)
- rings
- main bearings

How anal does one need to get for a maximum effort, high output engine? (i.e., I know some of this might be overkill for a street rebuild, but that's NOT what I'm doing here...)
Have I overlooked anything?

Also, I'm still really vacillating on the idea of a Fidanza lightweight flywheel vs. going with the stock unit...just can't find enough empirical or anecdotal evidence to firmly convince me one way or the other...there are advantages to both, and I need to make a decision since the flywheel is part of the balancing work that must be completed before I can start assembly on the short block. Thoughts?
_________________
erstwhile owner of just about every 924 variant ever made

[Joes924Racer]

Depends on you. and your anality.
Ive been quated 150 bucks for a good balancing of the rotating mass.
Here the motor revs quicker with the fidanza I say go for it. but thats just me.
if you can afford it & money not an issue at all do it. Really go for it.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[bass gt]

Dan,

Anything that is part of the rotating mass should be balanced. So yes, that means, everything from one end of the crank to the other, so clutch, cover, flywheel, crank, pulleys ect. The pistons and rods should be balanced as a set. So find the lightest of the bunch, and bring all others down to that weight +/- 1 gram. This applies to rod assemblies, pistons ect. Be realistic with your planned RPM limit, and all should be fine.
Re the ali flywheel, i can stronly recommend it. It will make the car a pig in traffic, as te revs flare, and it will be very easy to stall, but in terms of performance, a lightened flywheel is up near the top. The traits that make it a pig in traffic will make it sing once on song!!! Mine revs soooo freely, both up & down, but is a sod to just creep the car around.

Steve
_________________
Front Wheel Drive is the Devil's work.

[ideola]

Thx for the responses guys...

...so just a bit of elaboration from those that have done it before, what about the bolts, bearings, and rings...do these tiny items make enough of a difference that they need to go in as well?
_________________
erstwhile owner of just about every 924 variant ever made

[bass gt]

[ideola]

Perfect, thanks!
_________________
erstwhile owner of just about every 924 variant ever made

[peterld]

Hi Guys, There is a great little book I stumbled upon about ten years or so ago which really puts all this stuff into perspective and kind of summarises all the things I'd heard or learnt about building a motor. Great for the half serious DIYSer like me. Its an English publication which I actually found in a store in San Francisco on a visit there in 1998, and I've subsequently bought its companion title by the same author.
Its called "4-Cylinder Engine Short Block High-Performance Manual" by Des Hammill, part of the SpeedPro Series of books put out by Veloce Publishing. www.velocebooks.com or www.veloce.co.uk
I thought it was a great read and if you are going to spend the big dollars on a top line motor then this (or something similar) is a must. Just my thoughts. Cheers Pete

[Rich H]

I had that but can't find it now.

Frosts Car Restoration (Google it) sell the whoel collection IIRC.
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

[ideola]

Just found a pretty good online article:
Engine Balancing Explained
_________________
erstwhile owner of just about every 924 variant ever made

[Mike9311]

nobody noticed a detail in this pic yet in the other "anything exciting.." thread. Its a tiny detail in the pic



that's how anal...or crazy is more like it

The 80NA that is being worked on right now (longest running project ever) has everything dynamically balanced (not statically).
_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car

[ideola]

Holes in the cam lobes...
_________________
erstwhile owner of just about every 924 variant ever made

[emoore924]

Probably not actual holes, just drilled-out areas to balance the cam lobes. Seen this on a crank but not on a cam.

[v8carreragts]

Don't forget on the rods you need overall weight to be within 0.5 gram AND the weights of the big and small ends also need to be within 0.5 gram. For this you need to make up something to hold the rod level in the bore while you place the end on a scale. Actually I am anal about the pistons and rods and take the time to match then to 0.1 grams. I use a digital scale that is accurate to .01 gram.

The pistons need to match along with the pins. You need the weight of the rod bearing and the rings and pin circlips. When you go to get the crank balanced they will want all of these weights. (If they don't ask, go somewhere else) You should also give then the flywheel, complete clutch and the front pulley along with the fasteners.

I balance every engine I build. On V engine a 2 ounce/inch of imbalance at 4000 RPM's works out to around 55 pounds. Just think of having one piston/rod with a 55 pound weight attached. If it is just an everyday grocery getter that rarely sees 4000 RPM's it may not be necessary. But if it will be used for performance and you are using anything other than the original pistons and rods get it balanced.

[Mike9311]

Holes in the cam lobes and all the way through simply because that was the only place to get the weight off. The holes are extremely conservative in size (look at a Desmo Ducati cam for larger hole examples). Other areas were ground as well. I had never heard of a balanced cam either so why not try? In the end the ms2/edis conversion allowed for a custom counter weight at the end of the cam which was also needed. Holes in the lobes were not enough. The original cam gear was also lightened but in a way that was to help act as a counter weight based on trial spin ups. That didn't work exactly as planned since there was a lot of dynamic crossover as the balance improved. Its an experiment and we will see how it turns out.

The rods are also balanced both big and small ends following the proper procedure. The normal fixtures were made for this as well ( I need to take pics). Everything else too. Flywheel, clutch, etc. The inline 4 can't be balanced perfectly but you do what you can, if you can. I will report back of course once its running.

This is for the 80NA in my sig BTW. There are others things going on as well. If it runs this summer it won't be with all the changes but it will have a some.
_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car