Flywheel Alignment

SimonWright · **Posted:** Mon Mar 15, 2010 3:45 pm

There's a deeper backstory to this that might be forthcoming but for now let's keep this theoretical...

Why must the flywheel be aligned on the crankshaft? My guess is that the ECU uses it to determine cylinder position. Is that why the funny "cog" on the engine side of the flywheel has one set of teeth missing?

Simon

Aaron Buckley · **Posted:** Mon Mar 15, 2010 4:16 pm

SimonWright wrote:

There's a deeper backstory to this that might be forthcoming but for now let's keep this theoretical...

Why must the flywheel be aligned on the crankshaft? My guess is that the ECU uses it to determine cylinder position. Is that why the funny "cog" on the engine side of the flywheel has one set of teeth missing?

Simon

I've never seen a flywheel that had a specific alignment (other than what is the front and what is the back).

I think it would be odd to have a Crank Position Sensor read off of the flywheel, but I've seen stranger things. - AB

SimonWright · **Posted:** Mon Mar 15, 2010 4:46 pm

My flywheel has 6 bolts in a slightly asymmetric pattern. It'll only go on one way.

What is the purpose of the crank sensor then? Just to count RPMs?

JamesShort · **Posted:** Mon Mar 15, 2010 4:47 pm

SimonWright wrote:

My flywheel has 6 bolts in a slightly asymmetric pattern. It'll only go on one way.

What is the purpose of the crank sensor then? Just to count RPMs?

And ignition timing.

SimonWright · **Posted:** Mon Mar 15, 2010 5:02 pm

JamesShort wrote:

And ignition timing.

Ah ha! So it does need to know where the crankshaft is. Although doesn't it revolve twice for each spark? Perhaps that's dictated by plugging in the right wire to the coil. Are the fuel injections aligned with the spark signal? I feel like such a newbie.

Simon

jeremy gast · **Posted:** Mon Mar 15, 2010 5:18 pm

alot of manufactures also do it for balancing to a certain extent. i know we just had a motor installed on an altima and the flywheel was one bolt off and it ran but was throwing all kinds of timing codes, lined it up and bam it is all done.

BretLuter · **Posted:** Mon Mar 15, 2010 6:34 pm

Aaron Buckley wrote:

SimonWright wrote:

There's a deeper backstory to this that might be forthcoming but for now let's keep this theoretical...

Why must the flywheel be aligned on the crankshaft? My guess is that the ECU uses it to determine cylinder position. Is that why the funny "cog" on the engine side of the flywheel has one set of teeth missing?

Simon

I've never seen a flywheel that had a specific alignment (other than what is the front and what is the back).

I think it would be odd to have a Crank Position Sensor read off of the flywheel, but I've seen stranger things. - AB

BMW 325e's and 528e's used 2 sensors that read a small square "pin" on the edge of the flywheel in the same way most cars read off the front crank pulley. If the sensor(s) was bad or the pin fell off or got knocked off (commonly happened during tranny installation) the car would not start + run.

Older BMW's have timing marks on the flywheel, you shoot the timing light (remember those?) down through a hole in the top of the tranny bellhousing and you can then line up the timing marks by moving the distributor (remember those?????).

Even more modern BMW's have a specific way to align the flywheel- most have 6-8 bolts that hold the flywheel to the crankshaft, but the flywheel has one hole that is larger than the others, and the crank has a collar on one of the bolt holes, so that the flywheel will only fit on the crank one way.

JamesShort · **Posted:** Mon Mar 15, 2010 8:21 pm

Yep, wankel engines have asymmetric flywheels for balancing.

KendtEklund · **Joined:** Tue Mar 27, 2007 7:29 pm **Posts:** 1204

BretLuter wrote:

BMW 325e's and 528e's used 2 sensors that read a small square "pin" on the edge of the flywheel in the same way most cars read off the front crank pulley. If the sensor(s) was bad or the pin fell off or got knocked off (commonly happened during tranny installation) the car would not start + run.

Ask Sean and Walter how we learned this :oops:

SimonWright · **Posted:** Tue Mar 16, 2010 5:27 pm

FYI Here's a pic of my stock flywheel, engine side. You can see the missing teeth on the sensor wheel at the 3 o'clock position. I think the three holes on the rim are from balancing.

jeremy gast · **Posted:** Tue Mar 16, 2010 8:06 pm

the three drill holes on the ledge are the factory balancing

SimonWright · **Posted:** Thu Mar 18, 2010 1:22 pm

OK, so the backstory is that my replacement, lightweight flywheel wouldn't fit. I just heard back from the manufacturer that it is a manufacturing flaw. They will take it back but can't replace it for a couple of weeks when they've built the replacements.

I do have the option of a refund but I then 'll have to source another flywheel. Car is in pieces and I really want to get it back together this weekend. Picking up transmission tonight.

After speaking with the manufacturer's tech guy a third option is to elongate the one hole that is misaligned. It needs to be elongated by about 2 mm...

I could have at it with a file but I think it probably should be machined. Any suggestions?

Simon

Scott Johnson · **Posted:** Thu Mar 18, 2010 3:30 pm

Have at it with a file. It's close enough to the center of rotation that I wouldn't be too worried about the balance.

JamesShort · **Posted:** Thu Mar 18, 2010 3:40 pm

But on the other hand, if the input shaft isn't perfectly coaxial to the crank due to the pilot bearing no being coaxial to the crank, I wouldn't think this is ideal.

SimonWright · **Posted:** Thu Mar 18, 2010 4:04 pm

The five other bolts are good. They snug the flywheel down completely. So I know the flywheel is centered and aligned properly (that's also what the the tech guy said). At most I'll probably be removing a gram of aluminum. And, like Scott said, it's pretty close to the center so effect should be minimal. And this is on my Rally car so I'm guessing I won't notice.

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Flywheel Alignment

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