Cambelt stretch during installation
Hi all,
I'v done a head job on a DKZ head (thanks again welshpug for the help with the valve springs), with a D6B camshaft (two marks near the distributor end of the cam) and I've followed the Haynes procedure to fit the cambelt (Contitech). The head has been shaved just to clean it up (minimal material removed), and the head gasket was a 'normal' item from an Elring seal kit.
I've fitted timing dowels in the cam and crank pulley. I've put on the belt, and tensioned the roller by hand. I did two revolutions of the crank, and checked if the timing dowels still lined up (they did).
However, when I then tension the belt until I can just twist the the long end of the belt 90 degrees with two fingers, the timing marks do not align anymore. The crank timing hole is now about 3mm out. Is this correct?
Does anyone have the cam timing specs of the D6B so I can check? (I'm already looking forward to finding true TDC....)
Okay. After a lot of back and forth, I failed in my attempts to get an adjustable cam pulley delivered on time (I'm taking the car to scotland next monday to do the north coast 500).
First, I refitted the original cam pulley. Then I checked the timing. With the timing hole in the camshaft roughly lining up, I set the crank at 90 deg BTDC/ATDC by using a vernier caliper through the spark plug hole, taking car that I held the caliper the same way each time. This went really well, I could reliably locate this point within 0.01mm of piston movent, which translates to about 0.01 degree of crankshaft motion. The actual accuracy will be a bit less as it assumes a perfect cilinder head and perfect pistons. The crankshaft timing hole almost lined up. Piston 1 is now coming up in the exhaust stroke. The cam spec (11.5 deg btdc, 234.5deg duration) is not quite sufficient, as the lift at this duration is not given. I fitted a printed out protractor to the distributor side of the cam. With this, I measured a '-0.05mm' lift duration, by finding the points on the cam where I could just slide a 0,05mm feeler blade between the lobe and the tappet (both of piston 1 inlet valve, so valve clearance differences don't mess it up). I could reliably find this point within one degree of cam rotation. Half the difference between the mentioned duration (234.5) and measured '-0.05mm lift' duration (can't remember what it was, something like 280) is then subtracted from the -11,5 degree btdc (which is at degree 0 of 234.5), and setting the crank at this point (using the camshaft protractor and a 2:1 crank-cam rotation ratio), should allow me to just slide a 0.05mm feeler blade under it. Adding half the difference between the mentioned duration (234,5) and measured '-0.05mm lift' duration to the 46mm bbdc figure for the valve closing gave me the second point where I should be able to just slide my feeler blade between the cam lobe and piston tappet.
Luckily, it all ended up right on spec. Much ado for nothing, but I did have a nice time wrenching with my dad. It did require me to get a paper to write all the angles down, because it gets hazy if you need to convert back and forth to camshaft and crankshaft degrees and tracking everything.
I got the APK (Dutch MOT) this week, coming saturday is a 500km shakedown run, and if everything goes well, I'm on the boat monday
