How can I time the Crank Position sensor on an R850

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YKralph
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How can I time the Crank Position sensor on an R850

Postby YKralph » Sun Jun 24, 2018 12:54 pm

Hi, I hope someone can help me. I apologise in advance if I don't get all the technical terms right.
I've got a Citroen 2CV, into which which a guy called Pete Sparrow (sparrowautomotive.co.uk) has shoehorned an R850 engine. It uses an adaptor plate, designed by Pete, to fit the 2CV flywheel to the BMW crank and thence the Citroen gearbox.
My problem is that the engine I bought had had the crank position sensor removed (along with a lot of other stuff) A secondhand sensor was fitted and it seemed to run OK for about 2000 miles, then just stopped. It turned out to be a broken crank position sensor (somehow the moving part had worn away the static part... I'm sorry if that sounds a bit vague, but I haven't seen the damage) The guy who fitted a new sensor said that the old one "Wasn't bolted down" With the new sensor fitted, it will start (reluctantly) and run for about 20 seconds.
A couple of questions...
How could the bolts be "loose"? Could the threads in the crankcase be damaged?
Would the timing being out explain the engine cutting out after 20 seconds?
How can I time the sensor? Can it be done statically? If not, what angle advance at what RPM?
My brain is beginning to hurt now, so I'll leave it here and hope that someone knows what I'm talking about and can help.
Best Wishes, Ralph.

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george baker
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Re: How can I time the Crank Position sensor on an R850

Postby george baker » Sun Jun 24, 2018 1:08 pm

Hi
find Realoem. com for pictures of what should be there.

Search this site for "Hall Effect Sensors" and read about both Oil and Airheads, there will be links to external articles. Specifically read Ced's (Galactic Greyhound) posts on HES replacement at 50,000 miles.

Get us some pictures if you can of the sensor fit.

Sorry I can not be more useful atm

George
Member 21, R100R, K75 and a Hyosung 250 FOR SALE

YKralph
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Re: How can I time the Crank Position sensor on an R850

Postby YKralph » Sun Jun 24, 2018 2:02 pm

Thanks for the tips, George
Ralph

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Galactic Greyhound
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Re: How can I time the Crank Position sensor on an R850

Postby Galactic Greyhound » Sun Jun 24, 2018 5:13 pm

Hi, I hope someone can help me. I apologise in advance if I don't get all the technical terms right.

Hi Ralph!

I've got a Citroen 2CV, into which which a guy called Pete Sparrow (sparrowautomotive.co.uk) has shoehorned an R850 engine. It uses an adaptor plate, designed by Pete, to fit the 2CV flywheel to the BMW crank and thence the Citroen gearbox.

I had a Citroen Ami and a Citroen 2CV Charleston.

My problem is that the engine I bought had had the crank position sensor removed (along with a lot of other stuff) A secondhand sensor was fitted and it seemed to run OK for about 2000 miles, then just stopped. It turned out to be a broken crank position sensor (somehow the moving part had worn away the static part... I'm sorry if that sounds a bit vague, but I haven't seen the damage) The guy who fitted a new sensor said that the old one "Wasn't bolted down" With the new sensor fitted, it will start (reluctantly) and run for about 20 seconds.

OK, the 'crank position sensor' is the 'HES (Hall Effect Sender) Ignition Trigger Unit' usually called the 'HES.
The moving part of this is a cupped timing disk with a slot in it.
The timing disk is normally glued to the back of the crankshaft pulley which is keyed to the crankshaft.
The disk itself is indexed to the crankshaft pulley by means of a metal tab which fits into a hole on the pulley before the disk is glued.

Quite often, when the crankshaft pulley is removed, the glue fixing the disk to the back of the pulley has failed and the disk then falls off the pulley. I think that this is what might be meant by ' ...(somehow the moving part had worn away the static part... I'm sorry if that sounds a bit vague, but I haven't seen the damage) The guy who fitted a new sensor said that the old one "Wasn't bolted down"...

It should not be possible for the rotating cupped slotted disk to come into contact with the fixed HES Trigger Plate unless:

a. The Trigger Plate was not properly screwed to the inner front engine cover.
b. The rotating cupped slotted disk is damaged or not fixed correctly to the crankshaft pulley.
c. There is movement of the crankshaft due to bearing failure.

Note that when the bolt fixing the crankshaft pulley is tightened, the pulley and the timing disk are ALL clamped together against a boss on the crankshaft so it does not matter if the glue fails then as nothing can fall apart.
It is ONLY when the crankshaft pulley is removed that the disk can fall off the back if the glue has failed.
The glue is only there to keep the disk attached to the pulley when the pulley is removed.
The disk can easily be re-glued to the pulley if the glue has failed after making sure that the tab on the disk is indexed into the timing hole in the pulley.

There are TWO HES sensors on the fixed Ignition Trigger Plate which works with the rotating disk - the TOP HES sensor is for the Ignition Timing, the BOTTOM HES sensor is for the Fuel Injection timing.
Both of these HES sensors send digital timing pulses to the Motronic ECU in two separate pulse streams.


A couple of questions...
How could the bolts be "loose"? Could the threads in the crankcase be damaged?

See above, the cupped timing disc is glued to the back of the crankshaft pulley - there are no 'bolts'.
The triangular Ignition Trigger Plate mounting the two HES sensors is fixed onto the inner front engine cover by THREE screws (I think 5mm screws). These screws also allow the slotted Ignition Trigger Plate to be Retarded or Advanced (I think around +/- 5 degrees).
The Trigger Plate is normally set up in the mid-position.
The screws should be soaked in penetrating oil overnight before attempting removal or they might shear off in which case they will need to be drilled out, a Helicoil fitted and new screws (after applying copper anti-seize grease to the threads).


Would the timing being out explain the engine cutting out after 20 seconds?

No - the timing variation on the Trigger Plate is only about +/- 5 degrees.


How can I time the sensor? Can it be done statically? If not, what angle advance at what RPM?

As above, by adjusting the Trigger Plate.
Yes, it is done statically with the engine at TDC ('OT' mark on the BMW Flywheel rim (which you won't have fitted as it's been replaced by the 2CV flywheel)).
Set the Trigger Plate to the mid-adjustment position and you won't be far out.
There is an 'Oilhead Timing Box' which can be made quite simply and this can test the HES and set the Ignition Timing more accurately - see the link below:
Oilhead Timing Box: http://users.rcn.com/dehager/service/oi ... ng_box.pdf


My brain is beginning to hurt now, so I'll leave it here and hope that someone knows what I'm talking about and can help.

See this link by Dana Hager about the HES Ignition Trigger Unit - it explains all you need to do/know:
Oilhead Ignition Trigger Unit: http://users.rcn.com/dehager/service/oi ... ensors.pdf




CUTTING OUT/NOT STARTING

It is very likely that your Ignition Trigger Unit has failed and this is why your engine stopped and will only run for 20 seconds - this is a common fault.
It is due to the failure of the wiring insulation in the sub-harness between the Ignition Trigger Unit and its connector.
However, do all the other checks first as given in the link before replacing the Trigger Unit.
The Ignition Trigger Units only have a lifespan of about 50,000 miles before failure due to this wiring insulation problem.
You can re-wire them but most folks just purchase a new Ignition Trigger Unit from Motorworks, Motobins or James Sherlock (all trusted BMW parts suppliers) for around £150 and fit that.

NOTE: It is NOT possible to fully test an Ignition Trigger Unit on the bench because the exact working environmental conditions cannot be replicated.
If one of the HES has failed completely then that will show up on testing but most times the problem is intermittent due to the wiring insulation failure.

It will also help you if you get a used BMW R850 Haynes or Clymer manual off Ebay and this will cover your engine servicing.

FURTHER READING

Oilhead - Not Starting/Running: viewtopic.php?f=69&t=21616



Best Wishes, Ralph.

See how you get on Ralph and post here again if you have any questions.
Let us know how it goes

Photo: HES Wiring Failure
Click to Enlarge/Save As
HES wiring insulation failure.jpg
Photo: Dagda [BMRC]
Ref: http://www.bmbikes.org.uk/Forum/viewtop ... 79#p132279
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Ced.

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Sent by Boson Quantum Transmission from the Starship 'Galahad'.
http://www.researchgate.net/publication ... ing_bosons" - It works!

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Re: How can I time the Crank Position sensor on an R850

Postby YKralph » Mon Jun 25, 2018 9:43 pm

ImageHi Ced, thanks for the reply... I’m building up knowledge and confidence to tackle the job - I’ve checked out the link to the Timing Box and I’m sure I can make that; and a YouTube video showing the job on an R1100 (I think)
I know I can find TDC and, after removing the starter motor, can mark a tooth and the bell housing for future reference and maybe lock the flywheel with a couple of “Mole” wrenches (?)
Watch this space...
Ralph

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sykospain
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Re: How can I time the Crank Position sensor on an R850

Postby sykospain » Tue Jul 03, 2018 3:36 pm

An amazingly thorough, detailed, painstakingly prepared and beautifully edited WORD document tutorial from the esteemed Mr. Hager on the HES repair routine. Nothing short of fabulous. I've downloaded and saved it for future ref when my 26K miles Rockster eventually sweats out its HES wiring harness. It's a 2004 model, by which time I gather Berlin might've got around to sourcing a more heat-resistant cabling set for attachment to the unit.

And YKralph - ¿ have you any pics of the BMW 850cc boxer motor fitted into the 2CV engine bay ?
As a Citroën fan, I'd be very interested to see how it looks.
Regards from sweltering Andalucía,
AL in s.e. Spain
This is the list of people I'd trust with my bike.


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