oh dear....... a tale of timing chain woes

[oz_johnno]

Greetings,
I tee'd up a time with a local member of my bmw club for him to help me change my timing chain on beryl (black 86 R65).  we marked the timing chain and took of the timing chain.  we then had a bugger of a time putting the new chain back on, but we did it.  I left the timing cover of so I could check the timing but when I hit the starter button, the bean can started jumping up and down !!

So I took the bean can back off, made sure it meshed int the off center lugs and kicked her in the guts again....... this time the bean can didnt jump up and down, but it still wouldnt start.

we took the plugs out and yes there was spark there......

Im wondering what the problem could be?

Do you think I would have done damage having the bean can lugs not being meshed the first time?

what do you guys reckon?

OZ

[Barry]

Do you think I would have done damage having the bean can lugs not being meshed the first time?

I doubt if it completely destroyed the lugs as they are quite substantial. It's not even possible to fit the bean wrong because the drive is offset. The worst you can do is fit it loose and it sounds as if that's what you did.  

Might be a timing problem either ignition or valves.

[georgesgiralt]

Hello !
Actually, the lugs could be centered and the can installed anyway ! As we have one ignition spark per revolution (double output coil), the position of the can versus the cam shaft is irrelevant.
I cant see two problems :
1) the timing chain is not properly installed and you've a teeth out of alignment
2) the bean can was far from the timing point during your tests.

[oz_johnno]

I rang 'old mate' this morning and he seems to be convinced that there is something wrong with the bean can !!  He has it pulled apart all over his work bench this morning.

when we ran the engine we could hear no crunching or banging sounds as valves smashed into pistons, so I doubt it would be that.....

heres hoping.

OZ

[tvrla]

Unless the bouncing around dislodged something in the bean can, cam timing is the logical first place to look. Since there was spark - I very much doubt the problem resides with the bean can.

[oz_johnno]

Yeah I reckon its a problem with the timing.  In the haynes manual both the crankshaft and the camshaft pullys had thumping great lines on them to line up.

I saw a mark on the Camshaft (bottom?) pulley but not on the Crankshaft so I didnt have anything to to line up with.  what we did was put the camshaft mark at 12 oclock and marked with liquid paper.

What I'm thinking is we have the spark firing at bottom dead centre.......

Comments?

[Barry]

I don't see how you could have the spark at BDC on both cylinders.  Because the beancan is driven off the end of the camshaft and because the offeset drive means you can't fit the bean can wrong then if the ignition timing is miles out so is the cam timing.

If you have a degree wheel you could try and check the cam timing. It's not an easy thing to do accurately but if the timing is miles out it should be obvious.

  Inlet opens                16 deg BTDC
  Inlet closes                44 deg ABDC
  Exhaust opens            56 deg BBDC
  Exhaust closes             4 deg ATDC

[oz_johnno]

I guess the big question now is how much damage have I done turning the engine over with the timing out of spec.

when I turned it over it didnt seem to make any noises out of the ordinary that I could hear......... do you think this would indicate that the motor was still ok ??

Cheers


John

[montmil]

The primary concern is having contact between the valves and piston top! With the spark plugs out, carefully rotate the engine by hand and "feel" for any contact. You will definitely know as the engine will be stopped from rotating. Be Careful...

The small timing mark on the crankshaft is hidden by the sprocket. If the sprocket is removed, there's no real issue in lining up the crank n' cam sprocket marks.

I'm trusting to my memory here so hope if I'm speaking out of school someone will chime in...

Carefully rotate the engine so that the right-side piston is at exactly TDC. The dot on the larger camshaft sprocket should be at 12 o'clock. Again, IIRC from my last timing chain replacement adventure.

There's an excellent lesson here, lads. Before pulling off that old timing chain -and with the cam sprocket's timing "dot" at high noon- mark the location of the corresponding crankshaft sprocket tooth. Paint, Sharpie, whatever.

[tvrla]

I don't think you have anything to worry about as far as engine damage goes. There would have been metal to metal contact sounds and even a refusal to rotate completely. Do as Monte says and check if the marks line up.

[oz_johnno]

*phew*

we did a compression test with the following results

LHS = 50psi
RHS = 90 PSI

not good  

Looks like she could do with a head job (couldnt we all?)

[Barry]

Was the compression test done with the carbs off or at least with the throttles fully open and the pistons held up ?  

If the inlets tracts are not totally unobstructed to let the engine breath freely you will get an invalid low result.


It's still possible that out of spec valve timing could be the cause of low compression.  Think about the effect of inlet valves closing late ?

[tvrla]

The last thing changed was the cam chain. I assume it ran fine before that?

Logic and proper troubleshooting technique dictates the poor running (or non running) condition was caused by the last action taken.

So now we know it won't start because of low compression on one side. So?  

We really want to know about the timing marks and whether they align.

[oz_johnno]

I have given up and had the bike trailered to a specialist bmw shop.  I asked the guy if he could give me a diagnosis so I could get an idea as to how much the guy is gunna gouge me  

have read up on it and given the info I now know I would have gone about things a different way

Oh well, a lesson brought is a lesson taught my dad used to say........

OZ

[montmil]

We all want to know what the final outcome is, Oz. Keep us posted, will ya?