Originally Posted by Raylar

Mikael:

You are now saying that you had a metalic clicking noise coming from the front of the engine?
The stock timing chains on 496 (8.1L) engines built in the GM plant in Tonawanda all had looser tahn most engine timing chans and it was more noticble in the double roller marine HD chains. This was I have been told due to the robotic installation of the front of the engine and its timing gears and cahins and that GM designed the gear with a few thousandths extra smaller diameter to remove the tension on the chain during GM assembly. We have seen this on every 496 we have ever worked on and it has not ever been a problem as far as camshaft timing or noise. If if you install a new chain you will find nearly the same slop in the chain. For this reason I don't think your timing chain and gears are the issue unless they are damaged or improperly installed.
The camshaft sensor is just a simple on-off Hall effect sensor reading a 180 reluctor degree grove in the camshaft gear face. The location of the leading front edge and rear edge of that groove that tells the ECM when cylinders 1 and 6 are at their compression or exhaust TDC. This tells the ECM when the number 1 cylinder is at its compression point for firing and allows the ECM to locate #1 TDC quicker for quicker starts.
If the camshaft sensor circut is not operating properly the ECM will set a camshaft sensor fault code and the engine will either not start or start only after a lot of cranking and the engine will stay in a reduced power mode, not 100% power.
I suspect the metalic noise you describe may be from something else and that if it is big enough it could be setting off the knock sensor which retards timing, limits power and puts the Merc ECM into a reduced power mode.

If you have a scan tool, what is the ECM history file showing on some of these issues?

It sounds like you are saying that you did a camshaft change in this engine to convert it from a Mag to an HO engine?

Did the engine have this problem before you did the HO conversion? If it did not ,then I suspect the crankshaft reluctor was good then and after a camshaft only change the reluctor should still be undamaged or non-defective unless it was exposed to some other potential damage.

I would suggest a mechanics stethoscope with a metal tube to help pinpoint noises on or in the engine.

Try and locate your described engine noise as it may be affecting knock sensors. Also check for an exhaust header or manifold leak at the head to exhaust gaskets as these can sometimes sound almost metalic or like a knocking noise.

Since you have the Whipple supercharger you should also check the belt, lower pulley, tensioner and drive area of the supercharger to make sure you don't have a problem and noise there.

I hope when we get all the input facts and conditions sorted out so you can pinpoint your problem and get it repaired.

Its obviously winter in Sweden, so can you run the engine in the boat out of the water for some of these type of checks?

Best Regards,
Ray @ Raylar

Originally Posted by Raylar

Mikael:

Totally understand your weather versus work situation there in Sweden. We are spoiled here at Raylar in San Diego, we have just had three straight weeks of 75 degree weather so we get an excuse to work outdoors and boat pretty much all year!
That timing chain slop seems about normal if you are talking 1" of full deflection both in and out. New aftermarket 66 tooth double roller chains will tighten it slightly, but I still don't think thats your problem.
Lets just hope for an early spring in Sweden so you can get out of the igloo!
So much for Global Warming EH!

Best Regards,
Ray @ Raylar

Originally Posted by ZP'd

Who suggested to you to mod the 496?
You'd be better off ditching the add-ons, selling the motor and going blue. Seen this story way too often when trying for more with a perfect stock 496.

Originally Posted by pqjack

i have the same setup as you,MK,and i can run circles around a lot of blue ones.....