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some more dumb questions.....


Guest Anonymous

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Guest Anonymous

which way does the crankshaft pulley turn when the engine is running? (when viewed from the front)

when i put the pulley on with the engine all set at TDC, which mark to i line up with the pointer? (and dont say "the second" or something with no reference like haynes!)

cheers boys and girls and ladies and gentlemen of the jury...

ozgeorge

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Guest Anonymous

As viewed from the front, the crank pulley turns clockwise.

Think about the layout of the timing chain:

The crank sprocket pulls the chain downward which turns the cam sprocket clockwise, and as a result the chain is straight/tight thru the fixed rails between the two sprockets (right hand side as viewed from front.)

After the chain passes the crank sprocket, it's then on the "slack" side travelling upward. On this side (left hand, viewed from front) is where the chain tensioner & pivoted rubbing rail work to keep the chain steady untill it rounds the cam sprocket and gets increased tension from the direct pull of the crank sprocket.

Not sure what pulley you have on your crank, but typically there will be two closely spaced notches on the outer edge. BMW says to find TDC "the indicator must point at the second notch on the belt pulley when turning clockwise".

It's a good idea to confirm crank pulley notch alignments at TDC prior to installing the cylinder head, when you can directly confirm the piston's location.

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Guest Anonymous

id discovered that due to the notch on the crank shaft there is only one way the pulley can go back on... duh! with the front piston at the very top (TDC) the pulley goes on with the FIRST groove as pulley turns clockwise! not second... anyway... guess it doesnt matter... at least i know its all set at TDC...

i do have a few bolt size questions for you but i feel a bit scared to ask in case you get cross! ive applied for registration at mobile tradition but seems to be taking ages!

ozgeorge

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Guest Anonymous

"with the front piston at the very top (TDC) the pulley goes on with the FIRST groove as pulley turns clockwise! not second... anyway... guess it doesnt matter... at least i know its all set at TDC..."

George, I'd expect there is something amiss in the measurement. BMW has no reason to set any timing mark after TDC (which would be the case, if your first mark was TDC.)

There is variation in the marks dependent on which pulley you have. The newest versions of the stamped, single belt pulley have only one notch (TDC). The original stamped single belt parts had two notches, and the 3-belt pulleys had three timing notch.

In all cases, the last mark clockwise is TDC for cyl #1.

When there is a second notch preceding the TDC mark, it represents 3 deg BTDC for purpose of static timing (initial setting of the distributor prior to first running). This 3 deg BTDC mark is only a few millimeters away from the TDC notch.

When there is a third notch a good bit (~20 mm) earlier, that is the dynamic timing mark for 25 deg BTDC. Due to the smaller radius compared to the flywheel, setting timing with this mark is not as accurate as sighting the ball embedded in the flywheel.

I'd guess yours may have appeared to line up with the three degree BTDC mark due to a stack-up of small discrepencies.

The piston TDC is best found with using a degree wheel and a piston stop. Next best method is with a special bridge made to span the bore and hold a dial indicator on the piston.

There is plenty of room for error in this last method, mostly from the rocking of the piston. If you attempt to minimize that problem by carefully centering the dial indicator on the piston crown, you need to be mindfull the M10 has the pin position offset from center 1.5 mm and may not measure true height in the center.

The tougher issue is just how small the piston travel becomes near TDC. At 3 deg BTDC, the piston is only about 0.0025" short of its ultimate height in the bore, and things slow down much more as you approach the top and reverse travel.

If your's is still off the TDC mark when the pulley is fully tightened and actual piston TDC is measured correctly, then I'd expect it is from inaccuracies in the pulley, the woodruff key & slot, or a ground crank with improperly indexed throws.

In other words, if you do confirm the TDC mark on the pulley is wrong, don't be too quick to assume the 3 deg BTDC mark will work in its place !

" i do have a few bolt size questions for you but i feel a bit scared to ask in case you get cross! ive applied for registration at mobile tradition but seems to be taking ages! "

Sorry if I was short -- I was busy that morning, and only recalled that a week earlier I had provided you detailed fastener info & and suggested a way to find it on your own, and never saw a response.

Now I can see you were not really a lazy ingrate kitten killer ..;p)

Possibly the BMW ASAP catalog registration is slow due to Holidays? When I requested a password earlier in December, their response came in overnight.

Meanwhile, if you have any fastener part info questions, I can probably help.

Good luck with the build !

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Guest Anonymous

i have "custom ground" pistons in my block so it is possible that the mark not be exactly right...

however, i also wasnt aware of the narrowness of the travels you mentioned! i just kind of turned the crank till the piston started going back down and then turned back a smidgen... maybe this is not accurate enough?? i think ill take the head back off today and do it more carefully- see how close i can get it to the mark on the pulley....

i went through the registration process at BMW ASAP about 10 times using two different emails... no email! so i sent one to the techinical difficulties address... i've had an answer from them saying they're onto it... we'll see...

in the meantime, if you could tell me the size of the bolts that secure the clutchplate housing to the flywheel that'd be great, so i can confirm i have the right ones!

once again, thanks a lot

g

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