3.7 Litre 170 HP Mercruiser - Point Gap (Ser#592217)

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CPO1HankRCN

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Good day to all.

I have had great luck with posting questions on this forum so, here's another.

I have not be able to get anyone to give me a straight answer on the 'gap' for the points in my 3.7 L Mercruiser engine. I do not have a dwell meter as suggested by Stony, but I will get one in the near future.

I originally set the point gap at about the thickness of a dime (as I also lack a set of feeler guages/couldn't find one of the 3 or 4 sets that I had years ago) and the engine appears to work quite well, but I feel there is a bit more RPM than the 4800 that it is showing on the tach at WOT. It runs fine, but also appears to be labouring at RPM over 4000. I do realize that the trim will make the greatest difference in the world and will work on that the next time that I'm out. I guess my biggest problem is not knowing what the capability of the engine really is either, so consequently not sure what expectations should be from the 3.7 of the 1986 vintage.

I would like to have all at as close to spec as possible and go from there as far as performance is concerned.

Also, any comments on the electronic device that replaces the points and condenser on this engine? I have replaced the points and condenser in my 72 Mustang (351 Cleveland) with one of the units and it works great.

Any help from anyone on the point gap and especially the 3.7 owners on the capability of the engine would be greatly appreciated. It is pushing a 18 foot fiberglass 1986 SportCraft boat. Both Drive unit (ser #0A597696) and the Transom Assy (ser # A602395) are Mercruiser.
 
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stonyloam

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Re: 3.7 Litre 170 HP Mercruiser - Point Gap (Ser#592217)

Page 4B-1 of the manual that you downloaded, you did down load the manual right LOL? Just pullin your chain, 0.022, but that does not really tell you anything, as Don suggested you need to set the dwell, and not worry about the gap. BTW max WOT rpm for your engine is 4200 to 4600. It is not wise to exceed max WOT rpm. Need to get a second tach on the engine to confirm your boat tach reading, then change prop size to give max WOT in the proper range. You get maximum speed from a marine engine by selecting the proper prop pitch and diameter in a given WOT rpm range, and not by excessively high rpm.
 
Fishermark

Fishermark

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Re: 3.7 Litre 170 HP Mercruiser - Point Gap (Ser#592217)

We used to use a matchbook back in the day to get the points close to specs. ;)

But yes - you need to invest in some basic tools if you're going to work on it yourself. Feeler gauges and dwell meter will not set you back much coin.
 
achris

achris

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Re: 3.7 Litre 170 HP Mercruiser - Point Gap (Ser#592217)

Without feeler gauges or a dwell meter you have little chance of getting the gap right. Messing with the gap will also change the timing. So you're going to need a timing tight too. Simple requirement - get the right tools or have the job done by someone who has them.
 
achris

achris

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Re: 3.7 Litre 170 HP Mercruiser - Point Gap (Ser#592217)

stonyloam said:
:rolleyes:

Me too, but where are you gong to find a matchbook these days :rolleyes:
Click to expand...

I know some bars where I can get matchbooks, and a few other things... :D
 
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CPO1HankRCN

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Re: 3.7 Litre 170 HP Mercruiser - Point Gap (Ser#592217)

Again Don and Stony, thanks for the information. And yes, Stony I have downloaded the manual, but as you can see by my original question, I haven't necessarily read it page for page. Had I used it, I guess I wouldn't have had to bother either of you. Sorry about that.... I check out the manual first. But, having said that, I have learned another piece of valuable information regarding the max WOT RPM...... Real good information to know, I'll take it a bit easier on it the next time out!!!

BTW, how does one determine the proper prop pitch and diameter...... given the 4200 to 4600 WOT RPM for the 3.7? I have already ordered the dwell/tach/voltmeter Analyzer along with the Timing light, remote starter switch and the vacuum and fuel pressure tester.

Neither of you commented on the 'electronic ignition' unit that replaces the points and condenser???? Your thoughts..... seems like a very quick and permanent fix to the 'ever changing' gap in the points!

Again, thanks in advance for anything that you might be able to shed some light on.

Yours in boating.
 
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stonyloam

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Re: 3.7 Litre 170 HP Mercruiser - Point Gap (Ser#592217)

Props are a whole section by themselves. As a matter of fact go back to "forum" and look for the props forum. Read the"read this first' and gather the info asked for. Once you get running well, do a short WOT run and cross check your new /dwell tach with the boat tach to get a good reading on WOT rpm and work from there. Did not mention the electronic ignition, well cuz you didn't ask LOL. I have one, works fine. You would need Petronix Ignitor II (91146A) and the Flamethrower II coil, either oil filled (45011) or epoxy (45111). Remove and tape off the purple resistance wire and splice a stranded wire into the choke wire for full +12 V to the coil and module. Set the timing at 4 degrees BTDC and you should be good to go. Have fun. BTW not bothered at all.;)
 
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CPO1HankRCN

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Re: 3.7 Litre 170 HP Mercruiser - Point Gap (Ser#592217)

Thanks Stony for the information on the electronic ignition. That's a next year project for me, assuming that I keep this boat. It's an older boat and motor and from what I am gleaning, it has not been very well kept in the past years..... nor has it been used that much. I'd like to keep it for another year to get the 'bugs' ironed out of it and learn a bit more about these beasts!! The boat handles beautifully, is very responsive and is fun to play with. It does needs a bit more TLC and I think it will be a great boat (for my first boat).... other than a canoe!!LOL
The prop that is on it is definately the one that came with the boat when new and I suspect that once I get the point gap, dwell and timing right, it should run great. I've really got to get into the USA and pick up some more tools and upgrades like the electronic ignition as they are much cheaper and more readily available down your way.
Again thanks for the help...... most appreciated. I am hoping to do one last run for the Thanksgiving weekend (son-in-law and family is coming up from Toronto) and hope to get out on the big lake near us..... Lake Nippissing.
 
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stonyloam

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Re: 3.7 Litre 170 HP Mercruiser - Point Gap (Ser#592217)

If you are going to be using it late in the season there is the chance you could get some serious freezing weather, so you will want to take some steps to prevent freeze damage. Make sure the antifreeze in the engine is about 50/50 (get an inexpensive tester to check it), and between uses remove the aft plug on the heat exchanger to drain out the seawater. Just remove the exchanger plug, and the transom drain plug and let it drain. I do it right on the ramp when I pull the boat. Just make sure you put the plugs back in before you use it again LOL.
 
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