Engine Rebuild

[Jake Raby]

Anything is balanced if your tolerance of acceptance is wide enough. These engines are dynamically balanced very poorly from the factory; they just installed a 37 pound dual mass flywheel to smooth it out. The accountants said it was cheaper that way.

Study dynamic balancing and understand it before you can truly see how and why it is important to any engine.

Dynamic balancing and harmonics associated with a lack of it can even effect your ignition timing at upper RPM ranges with the M96 engine. Sounds crazy.

[pjq]

[QUOTE=Jake Raby;330736]Anything is balanced if your tolerance of acceptance is wide enough. These engines are dynamically balanced very poorly from the factory; they just installed a 37 pound dual mass flywheel to smooth it out. The accountants said it was cheaper that way.

Jake, I always enjoy your sarcastic comments!! haaaaa!

So, how is the balancing of these engines carried out, are weights added or shims used? I understand the precession of placing things back where they came from with the allowable tolerances but what actually is being balanced the crankshaft, pistons, camshafts??

[BYprodriver]

So, how is the balancing of these engines carried out, are weights added or shims used? I understand the precession of placing things back where they came from with the allowable tolerances but what actually is being balanced the crankshaft, pistons, camshafts??[/QUOTE]

Ideally most balancing can be accomplished by removing material from a heavy area to match the lighter areas. With pistons & rods each part is weighed individually to find the lightest part & then material is machined off to lighten the part until it weighs the same as the lightest part. With M96 engines the only part I have had to add weight is the pressure plate since there are few places to remove weight. Seems to me the flywheel & pressure plate are the biggest source of imbalance.

[Skootnasty]

Originally Posted by Jake Raby

Anything is balanced if your tolerance of acceptance is wide enough. These engines are dynamically balanced very poorly from the factory; they just installed a 37 pound dual mass flywheel to smooth it out. The accountants said it was cheaper that way.

Study dynamic balancing and understand it before you can truly see how and why it is important to any engine.

Dynamic balancing and harmonics associated with a lack of it can even effect your ignition timing at upper RPM ranges with the M96 engine. Sounds crazy.

Thats why you were such a HUGE advocate of the aluminum standard flywheel UPGRADE in WTI training at Orlando. Removal of the only factory vibration dampening capabilities is always a good idea.

[pjq]

If the home DIY'r is able to reassemble the engine to factory tolerences, get the weights correct on the crankshaft connections and then manually turn the crank and it feels smooth and rotates easily how do we know if we truley got it exact, because I'm getting the idea these Engines are suppose to be exact.
At a engine rebuild shop do they have machines to check themselves as they go?
What about when you finally bring the engine up to 6 -7000rpm and it must be smooth, do rebuild shops have machines for this or is it the experience of the builder?
Since balance is so important how can we replace our own clutch assembly and not mess up the fine balance, surely there is slight weight variations in the new parts? From what I read and see you take off the old flywheel, disk, plate and bolt on the new, there is no rebalancing happening at this stage?

Any thoughts?

[BYprodriver]

Originally Posted by pjq

If the home DIY'r is able to reassemble the engine to factory tolerences, get the weights correct on the crankshaft connections and then manually turn the crank and it feels smooth and rotates easily how do we know if we truley got it exact, because I'm getting the idea these Engines are suppose to be exact.
At a engine rebuild shop do they have machines to check themselves as they go?
What about when you finally bring the engine up to 6 -7000rpm and it must be smooth, do rebuild shops have machines for this or is it the experience of the builder?
Since balance is so important how can we replace our own clutch assembly and not mess up the fine balance, surely there is slight weight variations in the new parts? From what I read and see you take off the old flywheel, disk, plate and bolt on the new, there is no rebalancing happening at this stage?

Any thoughts?

It's more about preparation of the parts before you begin assembly. Insure every part you are putting into the engine is up to the task you are assigning it. (Daily driver for another 150K miles + autocrossing, or 30 minute lap sessions on track, or 24 hours of Daytona race.) The engine is only as strong as the weakest link. (part)
Find the best engine balancer you can send the reciprocating assembly to: Front crank pulley,bolt & washer, crankshaft, rods & bolts, pistons & pins & circlips, new flywheel & pressure plate, consider sending a 2nd flywheel & pressure plate since most balancing shops can't balance the flywheel & pressure plate without a crankshaft to mount on.
Usually very little material is added or removed as seen on the rods in the picture below.

[pjq]

To keep this topic in perspective, when these engines are new off the line how well balanced are they?

I thought Jakes statement below was just humorous sarcasism with a touch of exaggeration but is it really that way?
"These engines are dynamically balanced very poorly from the factory; they just installed a 37 pound dual mass flywheel to smooth it out. The accountants said it was cheaper that way."

If so that means there is alot of room for improvement on the stock engine, without resizing.

[Topless]

Essentially every mass produced engine will benefit from tighter engine balance tolerances. This is time consuming so car manufacturers don't bother but every properly prepared race motor gets a lot of attention to balance. In a well balanced motor, a couple of downshift over-revs result in a little valve float but no internal damage. A "loosely" balanced motor may suffer stretched rod bolts which will eventually back themselves out causing bad things to happen.

Just curious,
What guy considers rebuilding an m96 motor that has never considered engine balance tolerances? Of all the possible motors to rebuild, this one requires the most precision and attention to detail north of those crazy Italians.

[pjq]

Just curious,
What guy considers rebuilding an m96 motor that has never considered engine balance tolerances? Of all the possible motors to rebuild, this one requires the most precision and attention to detail north of those crazy Italians.[/QUOTE]

Topless sorry for taking so long to reply, work took priority. You also made me think about my reply. I've wondered how long it would take before someone asked a similiar question to me!Haaa! Below are my thoughts.

Amongst other traits, people have told me I’m practical, analytical and a perfectionist (I don’t wish this on anyone) therefore I don’t like making mistakes.

I live in an area where the nearest Porsche dealer is 4-4.5 hrs drive away.
There are two local shops that will change normal wear items on a Porsche but they don’t want to go further than that.
The nearest recommended Rebuilder is 1 hr drive away, but he hasn’t worked on a Porsche before. 4 hrs away the Rebuilder won’t rebuild but he has machined for Porsche engines before. Both of these guys do local race cars.

I think Glenn made a pretty good statement on his website (986fix.com) “"if your car doesn't deliver excellence, it is not impossible for you to do so." – Glenn.
Also recently Jake “Anything is balanced if your tolerance of acceptance is wide enough. These engines are dynamically balanced very poorly from the factory; they just installed a 37 pound dual mass flywheel to smooth it out. The accountants said it was cheaper that way.”
So if big Porsche won’t build a reliable precision Engine, yet their cars still run well (until they fail)and shops like Jakes are able to do it better and more reliable, than there is a chance I can fit in there somewhere.

If I don’t know how hard it is to rebuild a basic car engine then I don’t have anything to compare to. I will have to learn only one way, on a precision engine. It could be a great base line. I think ignorance can be a good thing as long as I remain open to be taught.
Just because we haven’t done something before doesn’t mean it can’t be done or we can’t do it, it may just be we haven’t been presented with a good enough reason to try. That being said one must know their limitations and know when to use Plan B.

When the engine failed I started reading more about them and what my options would be. I spoke to different Porsche people one of which was Jake Raby. There is a lot of helpful information in books and on internet forums like this one with good knowledgeable people willing to help out.
After seeing the cost and benefits for the different options and the residual value of my broken engine and considering I was going to have some spare time this winter , I was up for the challenge to see how far I could go with this new learning process(its been huge). I now see rebuilding will be the pinnacle of this challenge.

So for a practical person with minimal mechanical experiences none of this makes sense, I should have cut my loss and run but I was ready for a new learning challenge AND it was an impractical car I cared about (emotions, dangerous with value).

If I lived within an hours drive of Jake or some other reputable shop on these forums I would have sent my car straight to them BUT I would want to be allowed to be able to watch the progress and see this engine opened up.