Ignition Timing on GM 350

Author Message   Lee Krieg Posted on Friday, June 27, 2003 - 11:37 am:    I have a 1986 GM 350 Volvo-Penta I/O. The recommended timing setting is 8 deg BTDC at idle. If I set the timing at 8 deg it idles VERY rough, hard to keep running. If I set it to about 20 deg BTDC it purrs like a kitten and runs great on the water. Its a new boat to me and I upgraded from the old points ignition, and I had never checked the timing with the old points system so I don't know where it was to start with. What bothers me is, is running so far out of spec dangerous to the engine and why is it this way? All I can figure is the pulley has moved, a sheared key or whatever causing the mark to be in the wrong position. My idea it to "Power Tune" the boat i.e. run it on the water at cruise speed and adjust the timing to get the max RPMs and not worry about where the marks are. Some friends said this was a good idea, others said a bad one. Looking for opinions/suggestions. Thanks   Daniamarine (Daniamarine) Posted on Monday, June 30, 2003 - 05:54 pm:    TIMING FOR A BREAKERLESS SYSTEM IS GENERALLY 10 DEGREES BTC. YOUR RIGHT THAT THE HARMONIC BALANCER HAS POSSIBLY SLIPPED ON ITS HUB OR SHEARED A KEY. WHAT YOU NEED TO DO IS BRING THE NUMBER ONE CYLINDER TO TOP DEAD CENTER AND SEE IF THE MARK ON THE BALANCER IS AT 10 DEG.BTC AT WHICH POINT THE ROTOR SHOULD BE POINTING TO THE N0. 1 PLUG WIRE. IF YOU NEED ANY HELP YOU CAN CALL ME AT DANIA MARINE 1-800-748-7739. THANKS, GABRIEL   akriverrat Posted on Wednesday, July 02, 2003 - 09:57 pm:    be careful doing that because it can be very hard hearing the spark knock that will eventually destroy your engine. slipped balancer hub or jumped timing chain should be checked for. what did you upgrade ignition with?   Lee Krieg Posted on Thursday, July 03, 2003 - 10:53 am:    The ignition was replaced with a Sierra Marine upgrade. All I did was take the old breaker plate out and replaced it with a new plate with a pickup coil on it instead of points, put a plastic piece under the rotor (a magnet, I think), hooked up 3 wires and it started right up without changing the timing. I do not think the timing chain is out, the valves seem to be timed correctly because the compression is good and the engine runs well. What's the trick to precisely finding TDC if you can't rely on the timing mark and don't have the heads off. I've tried feeling through spark plug hole with a screwdriver, but this isn't very accurate. I guess I will have to try pulling the balancer to check for a sheared key. I have never done this before and as in most boats it's a tight fit in the bilge. I feel as if I have a problem I need to address but on the other hand I think "If it ain't broke, don't fix it".   akriverrat Posted on Thursday, July 03, 2003 - 04:58 pm:    that is probably a pertronix ign. and should have had little effect on timing. you aren't a ford guy are you? timing off gm cyl#2, ford#1? i've tried that.   Steve Posted on Thursday, July 03, 2003 - 08:18 pm:    Lee, to find TDC remove #1 plug,remove coil wire,if you have another person they can bump the starter while you hold your finger over spark plug hole. Otherwise use a compression tester. When you have compression,turn the crank manually until piston is at TDC.A section of coathanger or mechanics wire works well to feel when piston is at TDC. Good Luck,Steve   Jim Cooper Posted on Monday, March 08, 2004 - 05:13 pm:    Lee, Steve and Gabriel are right on. Once you have #1 piston at TDC, you will be able to determine where the mark on the balance wheel is. That should correspond to a 0 degree (TDC) mark on the engine or timing cover. Some marks may be for timing @ some degree before TDC, so be carefull to distinguish the different marks on the engine. Bottom line, if the balance wheel mark lines up with the TDC mark on the engine and the rotor is pointed exactly at the #1 spark plug wire on the distributor, then all is fine with the gears and balance wheel. Look further in to the electrical components or timing test equipment. By the way, I had bad luck using the Seirra module and switched to prestolite.   Jim Cooper Posted on Monday, March 08, 2004 - 05:22 pm:    Lee, Steve and Gabriel are right on. Once you have #1 piston at TDC, you will be able to determine where the mark on the balance wheel is. That should correspond to a 0 degree (TDC) mark on the engine or timing cover. Some marks may be for timing @ some degree before TDC, so be carefull to distinguish the different marks on the engine. Bottom line, if the balance wheel mark lines up with the TDC mark on the engine and the rotor is pointed exactly at the #1 spark plug wire on the distributor, then all is fine with the gears and balance wheel. Look further in to the electrical components or timing test equipment. By the way, I had bad luck using the Seirra module and switched to prestolite.   horace favaloro Visitor Posted on Saturday, September 01, 2007 - 11:19 pm:    I have a volvo AQ131A motor and the timing belt broke. I replaced it. I line the dot on the cam gear up with the mark on the valve cover, the #1 piston TDC and the distributor grar dot with the V on the plate behine it. Is this correct? I change the impeller also. When it runs over 2500rpm it over heats fast 2500rpm and less it runs fine why is it over heating?

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