Can't turn engine

[mulrik]

You are not going to believe this!!! Engine was working fine except I was a little insecure whether the injection was precise on time. So I removed and refitted it just like Haynes says, no problem in spinning the engine by pushing the car while in fourth gear. I alligned the cam and the crank precisly, was a little late before. I wanted to turn the engine by pushing the car in fourth once again, and I couldn't move it more than just a few centimeters. Now handbrake is off and I'm not in second gear either. I removed the chain from the camshaft sprocket and I could again turn the engine. I aligned the everything again and the engine won't turn. I'm 100% sure everything is aligned correctly and that I'm not 180 degrees of, but I can't figure out what is wrong. I know this sounds freaky, but what on earth is going on?

Can it in any way be possible for the degree marks on the crank to be out of sync with the position of the pistons? Can the chain be too tight? anyother suggestions? I'm dead sure I aligned it correctly and I am not on drugs or drunk, but I can't turn the engine???

Should say that the car was running prior to dismantling, albeit with heavy black smoke on acceleration which is why I wanted to time the injection which was out of sync as I also found out when I removed it.

Please anyone??
Ulrik


'67 250 SL Papyrus White 113043-10-000023

[ja17]

Hello Mulrik,
We can walk you out of this problem but you must do some checking first. Remove the spark plugs first just to make everything easier to turn. If the pointer on the crankshaft is at TDC the number one piston must be at the top (carefully check through the #1 sparkplug hole. The camshaft mark can be late but NEVER even a tiny bit early!
If the engine will not turn after checking this then the chain may be jambed. The chain tensioner can deflate and the chain can bunch up and jamb on the crankshaft sprocket, or possibly the timing gear sprocket. Take a strong flash light and look carefully at as much as you can. Look carefully at the chain tensioner sprocket, if it is depressed downward this might also be an indication that the chain is bunched up somewhere below.
The bad thing about pushing the car to move the engine is that as the car rocks back and forth the engine may go backwards for an instance jambing the chain. Please take a close look down the chain gallery and report back. You will probably have to get a ratchet on the crankshaft bolt and very slightly reverse rotate the engine to unjamb the chain. Next take up the chain slack by slightly reverse rotating the camshaft. Pump up the chain tensioner sprocket, check the timing marks and check for ease of rotation. I like to rotate the engine at least one complete revolution by hand in the correct direction as a final check on the timing. A mistake here can break a chain rail,bend some valves or break a camshaft!

Please check for any visible jamb up of the timing chain first. Long distance diagnosis requires a lot of acurate facts!

Joe Alexander
Blacklick, Ohio

[mulrik]

Thanks Joe I'll do that. But just quickly how exactly does the chain tensioner work?? I now its mechanical and hydraulic. Do you need to fill it with oil or does it pick it up by itself and how??

'67 250 SL Papyrus White 113043-10-000023

[ja17]

Hello Ulrik,
The chain tensioner is spring loaded and also uses hydraulic pressure produced by the engine oil. The cylinder head has a small oil resevour in the head just under the chain tensioner sprocket. This little pocket collects oil which is pumped into the tensioner making it very stiff.
You can check the tensioner by pushing down on the chain tensioner sprocket. If it moves downward easily the tensioner may be bad or the timing chain may be stretched.  The tensioner sprocket will move down slowly if a lot of force is applied. This is normal.

If the chain tensioner sprocket is all the way extended upward and the chain still has slack the timing chain may be stretched. These chains should be replaced every 100,000 miles or earlier if needed.

Joe Alexander
Blacklick, Ohio

[mulrik]

Problem solved!! The mechanical part of the chain tensioner does not provide enough power to tighten the chain. I refilled the oil chamber for the chain tensioner and pumped once or twice after i had alligned the cam and the crank that solved the problem, which means that the chain was running freely around the crankshaft sprocket previously.

Advice for the future DIY'er: remember to fill oil into the chain tensioner.
Thanks Joe for your help!!!!
Ulrik


'67 250 SL Papyrus White 113043-10-000023