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Replacing timing chains,

Hi guys
I posted in an erlier post that my timingchains where worn.
Now I have come to the point that I am replacing them with new masterlink chains.
I decieded to cut the old chain, link in the new, and turn the engine pulling the
chain along.
Before I started I checked the timing of the old chains. Both sides had 2.9 mm of lift and
acording to Waynes book it should be ~4.7mm for my engine (1977 2.7 cis).
Also I backed off every valve adjustment screw as much as possible to get some more clearence
turning the engine (Im I tinking right?) and removed the sparkplugs to make the engine easier to turn.
The right side went fine, the chain snagged a little but once it I got going it went round smoothly.
But on the left side.... I got the crank round ~360 degrees and then something restrikted the crank....
Its about 50 degrees after TDC for cyl #1. My fist thought was that the chain had sliped somehow
a piston hit a valve. But when I turned back to TDC for cyl #1 both cams was pointing straight (or very nearly)
up. Then the timing should be ok and the engine turnable, right?
I also went back to the stop and there I tried to screw in the valves tha where "on the lobes" and they could be
pushed in severel milimeters (I didnt feel any pistons).
Does anyone have any theory???


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Magnus
911 Silver Targa -77, 3.2 -84 with custom ITBs and EFI
911T Coupe -69, 3.6, G50, "RSR", track day.
Old 03-15-2005, 03:38 AM
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My guess. The cam moved and cylinder no. 1 is now at TDC with the valves in the overlap position (end of exhaust, beginning of intake) instead of both valves closed (end of compression, beginning of power). Or the left and right banks are no longer operating in unisyn. The starting point is TDC, no. 1 cylinder is ready to fire (both valves closed); no. 4 is at TDC overlap position with the cam dots oriented at 12 o'clock.

You could do an end-around and remove the left bank rockers to ensure all valves are closed and not creating any interference while you rotate the crank to the correct position. Be mindful of what's happening with the right side cylinders (4-5-6) while this is going on.

Sherwood

Last edited by 911pcars; 03-15-2005 at 12:30 PM..
Old 03-15-2005, 12:28 PM
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Yes, I thought so at first. But the cams have the 911 mark right up and the valves for number one are not "on".
Also I noted trying to go back it stoped some degrees before TDC #1.
So now I have movement about 90 degrees around tdc #1......
As I see it it cant be a valve Im hitting (asuming i am right that at TDC#1 both cams should be pointing up). Either the chain is snagging, foreign object somewhere or some other explanation...
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911 Silver Targa -77, 3.2 -84 with custom ITBs and EFI
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Old 03-15-2005, 01:51 PM
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Magnus,
I would try backing off all the rocker arm adjusters and see if that makes a difference with the allowable amount of crank rotation.

Something hitting the flywheel?

Chain bunched up inside the crankcase?

Sherwood
Old 03-15-2005, 01:59 PM
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I had this happen to me, its easy to bunch up the chain or have it bind on the sprocket. With an extra set of hands pull some tension on the loose end of chain as you rotate the engine.
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Old 03-15-2005, 04:56 PM
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Im leaning towards the chain theory, I have backed of the rocker arms.
I might have to remove the chain housing to make it abit easier.
I cant get to the car until sunday to try it out.
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Magnus
911 Silver Targa -77, 3.2 -84 with custom ITBs and EFI
911T Coupe -69, 3.6, G50, "RSR", track day.
Old 03-16-2005, 04:08 AM
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Found the problem!
I removed the left chainhousing and saw thar the chain had sliped of one sprocket inside the engine. I managed to get it on again and I could get the new chain around.
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911 Silver Targa -77, 3.2 -84 with custom ITBs and EFI
911T Coupe -69, 3.6, G50, "RSR", track day.
Old 03-26-2005, 11:37 AM
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cam timing on a '77 2.7 is 0.40 to 0.54mm lift at the valve, not 4.70mm.
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Old 03-26-2005, 11:51 AM
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I know, just a typo by me.... But worth clearing up, thanks.
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Magnus
911 Silver Targa -77, 3.2 -84 with custom ITBs and EFI
911T Coupe -69, 3.6, G50, "RSR", track day.
Old 03-27-2005, 11:10 AM
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