adjusting timing (Chev 305 IB)

[oldboat1]

I want to retard the timing slightly on my Chris Craft: 305 chevy, clockwise rotation. I don't remember which direction to turn the distributor to retard the timing. When I turn clockwise, the engine slows. When I turn counter-clockwise, the engine rpms increase. Can someone tell me what direction retards the timing?<br /><br />(I'm being a little lazy -- have a timing light, but in order to get a reading I have to pull apart the top cabin step to get access to the front of the engine.)<br /><br />Thanks.

 

[oldboat1]

Re: adjusting timing (Chev 305 IB)

FYI -- found the answer, folks. Counterclockwise rotation increases rpms, and advances timing. Turning the distributor clockwise retards timing (decreases rpms). This is for my clockwise-rotating engine.<br /><br />But I've decided I want to advance the timing slightly, because I get a smoother idle and acceleration, and believe it might run just slightly cooler in this summer heat. I'm not sure how top end rpms might be affected, if at all, but I'm more interested in lower range operation (say 2500 rpms and lower).

 

[Boatist]

Re: adjusting timing (Chev 305 IB)

You got it right as for direction, but I would be very careful adjusting it with out a timming light. Too far advance and motor can over heat or you could burn a hole in a piston. Too far retarded and motor will start easy but have no power and use lots of fuel. I would use a timeing light or I would adjust it at WOT by ear. Advance slowly until here some pinging then retard until goes away then just a little more.

 

[oldboat1]

Re: adjusting timing (Chev 305 IB)

Thanks, Boatist. I marked the position of the distributor after I timed it with the light, so the adjustment I'm fooling around with now is in reference to that mark. When I advance the timing just a bit off my mark, the motor sounds smoother and quieter -- rpms increased by about 300, so I backed off the idle adjustment screw to compensate. I'm looking for it to run just a little bit cooler, as I'm thinking I might have had it just a bit too retarded (My assumption is that running too far retarded will cause it to run hotter.) It's hot out and the water is warm now, but the temp was hitting 180 and that seems a little hot (goes back to about 160 after throttling down to about 1000 - 1200 rpms for a bit). When it warms up at idle from cold, it holds at a little under 150 (holds that temp indefinitely, if I just let it idle in the slip).<br /><br />If I understand you correctly, advancing the timing a bit might increase power (higher rpms?) -- but it could give me some pinging (a sign I advanced the timing too far). Based on your response, though, I might be wrong about the effect on engine temp -- advancing the timing might in fact make it run hotter (?)<br /><br />I'm making these adjustments at idle speed, and I guess you are saying that doing it at WOT would be better. I very rarely have run at WOT, and then for only short periods -- guess maybe the pinging would only be noticed at the top end, though, so I should at least try out the timing setting under load at something close to WOT. (Can I assume that rpms on the top end will likely be higher when timing is advanced? I usually run under 2500, although I think the manual calls for 4500 rpms at WOT -- maybe 5000.)<br /><br />Hey -- Thanks.

 

[Countrybois]

Re: adjusting timing (Chev 305 IB)

Sounds like you are getting the timing dialed in. Tell you how I did it, just keep in mind I'm no expert. I believe my balancer had slipped rendering a timing light useless. I ran her up to about 3000 rpm's advanced the timing until I could hear no further gains in rpm's and no spark knock(pinging). Made one heck of a difference on the water. As far as the temp, have you checked the condition of your impeller in your lower unit? Timing will affect the temp, but if you are getting up to 180, I would venture to say your supply of water is lacking.

 

[oldboat1]

Re: adjusting timing (Chev 305 IB)

Thanks, Countrybois. I believe the manual calls for a setting of 14 degrees before TDC on my motor, with its dual set of points. This is an old '77 Chris Craft with an OMC 305. I set it there last year, and marked the distributor for that setting.<br /><br />I think I'm not advancing it very much from the set mark -- surely haven't gotten to the point where rpms don't increase, but then I was making the adjustment at idle.<br /><br />I tried the new setting out over the weekend. The engine runs at about 165 to 170 degrees at about 2000 rpms, which is a little improvement. (thermostat is 140 to 165 degrees). It runs a little smoother than before, to my ear. Unfortunately, it turns over a little hard if I shut it down when hot, and then go back and start it after a bit -- problem I had before, and was advised that problem can crop up if the timing is advanced too far.<br /><br />I've had the boat about a year. The previous owner had a tuneup done about 6 mos before I bought it, incl a new impeller -- but it could be due for replacement. I rountinely do that when picking up a "new" outboard to play with, but have not done so with this inboard. I also haven't done a compression check, although was advised by the prior owner that the tuneup involved a check and there was nothing remarkable.<br /><br />appreciate the advice....

 

[Boatist]

Re: adjusting timing (Chev 305 IB)

OldBoat1<br />If you increase the timing too far the temp will go up, it will start to ping and if go too far can blow a hole right thru the piston. If the motor is kicking back or turning over hard when hot it is too far advanced. Running at wot and adjusting you will see changes in speed and rpms but not like when at idel. Rpms and speed will change very slow could take a couple of minutes.<br />Most engines have a 150 degree thermostat and will run around 170 when get close to wot. In fresh water best temp in around 190 like most car run today but in salt water over 170 start getting a lot more engine deposits of salt.<br /><br />I am not sure what type engine and manifolds you have but one common problem in motors run in saltwater is the manifold rust and scale comes off and pulgs up the exit holes in the exhaust manifold where water goes into riser. The first noticed effect of this is motor runs hot at higher rpm as can not get enough water flow thru engine and manifold to keep it cool. Slow down and goes back to 150. Happens is fresh water also but takes a lot longer. Manifold only last about 6 years in salt water if you flush saltwater out evertime you run it. Sooner if you never flush it out. Soon after see plugged up exhaust manifold, manifold will rust thru where water leaks into exhaust then runs down to the exhaust valve and rust it. Worse case while sitting water leaks into exhaust run back to open exhaust valve and into the cylinder and rust it then when try to start engine exhaust valve closes with water in there intake opens and sucks in fuel and air and closes then try and compress fuel air and water but since you can not comperss water it bends a rod or breaks a piston.

 

[oldboat1]

Re: adjusting timing (Chev 305 IB)

Thanks, Boatist. Just to clarify, are you saying the change in rpms is more radical -- more easily noticed -- when the timing adjustment is made at idle? If so, that means my "slight" adjustment (advance) might be a bit more than I realize -- and I should retard it a little. I don't know if it's considered "bucking," but the engine does sort of hang up when it's hot and I try to restart it (that's after I advanced the timing). It sounds like it would with a weak battery -- sounds like the starter has a hard time cranking it fast enough to start -- usually on the first crank (like the first revolution), then it frees up a bit and the starter turns it at normal speed.<br /><br />I've probably got a little more time on the exhaust manifolds, but I have to make work of installing my flusher valve -- had the boat about a year. I should probably put the valve in and check the temp when flushing as well -- think the increase in operating temp might also be a function of the bay and river water temps. -- now about 75 or 80 degrees, I think. The heat exchange can't be as good when the water used to cool the antifreeze mix in the exchanger is about 80 degrees, or so it seems to me.<br /><br />Thanks.

 

[Boatist]

Re: adjusting timing (Chev 305 IB)

Yes the change in RPM in nutural at idle will be fast and a big swing. On the water running wide open the engine has to move the boat to increase RPMS and that can take two minutes for a 100 rpm increase or decrease. You engine turn slow when hot because it is timed to fast and cylinder is fireing before the piston gets to the top so tries to turn engine backward. I would adjusted it with the timing light out on the water and make a run readjust and move a couple of degrees make the same run and compare results. If you do not see a big difference I would set it to specs and leave it alone. TOO fast can mean short engine life.<br />Water Temperature<br />I had no idea you have a heat exchanger and fresh water cooling. I would change the thermostat to a 180 degrees where engine runs about 190 and be happy. Only need the 150 degree thermostat to stop engine deposits actually runs better hotter. With antifreeze can run up to 220.

 

[oldboat1]

Re: adjusting timing (Chev 305 IB)

Good stuff, Boatist. I appreciate the time.<br /><br />I'm pretty much back at the original mark for timing (had set it at 7 degrees BTDC, according to specs for the engine -- not 14 degrees as I incorrectly indicated before). Your posts have made me less concerned about the temp.<br /><br />It is indeed fresh water cooled, but of course that means that raw water is used for heat transfer and runs at least through the risers and the transmission oil cooler. The manual calls for a 143 to 165 degree thermostat, and it looks to me like that is probably what is installed -- seems to open between 140 and 150, on the temp gauge, during warm up. I guess I can be a little less concerned about running temps of 170 or 180 degrees, particularly during hot weather.<br /><br />It's an old engine. I need it to be able to trust it, or it spoils the fun. It can probably stand a little harder use than I give it -- which is pretty much the situation I want.

 

[Boatist]

Re: adjusting timing (Chev 305 IB)

OldBoat1<br />I do not like to push my boat to the limit either. Yes with a heat exchanger you still use sea water to cool the exhaust manifold and riser. The standard thermostat is usually 150 for boats but same engine in a car will be 180 to 192 degrees. With a heat exchanger engine temp will run about 10 degrees hotter and that is good. Also do not have 50 degree sea water coming in to a engine running 170 degrees and that is also good.

 

[horndog]

Re: adjusting timing (Chev 305 IB)

you need to run it it at 3000rpms to get it timed correctly when the advancing mechanism kicks in, otherwise you are just doing the regular timing not the timing advance.<br /><br />I use to tune my car by "ear" and it worked, but it was a electronic ignition system, not mechanical like you and I have.