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Timing Specs 77/78 M90 635CSi EURO

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Klaus
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Timing Specs 77/78 M90 635CSi EURO

Post by Klaus » Fri Oct 12, 2018 7:22 pm

Can anybody please check what the factory timing is supposed to be for an 77 or 78 m90 EURO 635? I currently have it set with the 22 deg mark at 2200 rpm with both vacuum hoses disconnected and plugged. Engine has notable ping under heavy acceleration from about 3-5k rpm.

Thanks in advance,
Klaus

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Hefeweizen
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Re: Timing Specs 77/78 M90 635CSi EURO

Post by Hefeweizen » Sat Oct 13, 2018 7:57 pm

Klaus,
that is what I read also for my M90. Problem is that I do not see a timing mark at all at that RPM. I do see something at 1100 rpm that I think may be the timing mark. I do have still issues with my Throttle adjustment and get to my timing adventure again once I have that solved
Rainer
85 635CSi (Silver, Daily Driver)
79 633CSi (Red Euro, Project)

"If you think a good European mechanic is expensive, try a bad one!"

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Hefeweizen
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Re: Timing Specs 77/78 M90 635CSi EURO

Post by Hefeweizen » Sat Oct 13, 2018 10:58 pm

You can also visit http://www.firstfives.org/ .

The have a wealth of knowledge there. There is also a tech article under "Technical FAQ" on ignition timing. =D>
Rainer
85 635CSi (Silver, Daily Driver)
79 633CSi (Red Euro, Project)

"If you think a good European mechanic is expensive, try a bad one!"

m6dave
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Re: Timing Specs 77/78 M90 635CSi EURO

Post by m6dave » Mon Oct 15, 2018 7:53 am

Klaus wrote:
Fri Oct 12, 2018 7:22 pm
Can anybody please check what the factory timing is supposed to be for an 77 or 78 m90 EURO 635? I currently have it set with the 22 deg mark at 2200 rpm with both vacuum hoses disconnected and plugged. Engine has notable ping under heavy acceleration from about 3-5k rpm.

Thanks in advance,
Klaus
Question about timing - thanks in “advance” :mrgreen: :mrgreen:

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Klaus
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Re: Timing Specs 77/78 M90 635CSi EURO

Post by Klaus » Sun Oct 21, 2018 4:47 pm

:D ... no pun intended!

But on a serious note... can somebody please post a picture of an emission label showing the timing specs of an early M90 L-Jet. I know that the reference mark is at 22 degrees, I really would like to know what the target rpm is. The only reference is found so far shows 1700 rpm with both vacuum lines disconnected and capped.

Thanks!

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Hefeweizen
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Re: Timing Specs 77/78 M90 635CSi EURO

Post by Hefeweizen » Sun Oct 28, 2018 4:39 am

Previous owner painted over #-o
Rainer
85 635CSi (Silver, Daily Driver)
79 633CSi (Red Euro, Project)

"If you think a good European mechanic is expensive, try a bad one!"

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Brucey
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Re: Timing Specs 77/78 M90 635CSi EURO

Post by Brucey » Sun Oct 28, 2018 10:19 am

there is quite a lot of useful info on this in the E12 Haynes manual; the same engines are used and there are various different distributors and therefore target rpms.

Normally there is a 'knee' in the advance curve and this represents the position where the soft spring on the bob weights taps out and the harder spring becomes the dominant thing. The 'knee' position (rpm) varies with distributor design. The intention is usually to check the ignition timing at or close to the 'knee', the reason being that if there is wear in the spring linkages or a fault in either spring then it will usually create the largest error at this point.

If using a strobe light it isn't a bad idea to put some clearly visible marks (eg using typing correction fluid) on the flywheel at the correct positions. This makes the check far easier to do since the marks are always clearly visible, even if you are using the most basic (Xenon tube in series with a spark plug) timing light.

There is of course a basic problem with all this, in that petrol (gasoline) isn't the quite same now as it was forty years ago. This means that even if the engine is in tip-top shape, it mightn't like the original timing settings. This goes double for a Euro spec car; it would have been designed to run on 98RON (four star) leaded fuel, not the stuff we get now.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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Klaus
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Re: Timing Specs 77/78 M90 635CSi EURO

Post by Klaus » Mon Oct 29, 2018 4:26 am

Brucey, I looked at the FirstFives FAQ and came to the conclusion that I most likely have to play around with the timing on a experimental basis in order to find an acceptable setting. I agree with your statement about current gas quality, it does not even appear to be consistent from station to station of the same vendor. The only thing that scares me is that the audible sensation of pinging is at the extreme spectrum, it might be hard to find a setting that does harm the pistons this way.

Klaus

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