I have seen the electronic tachs that are digital, fairly inexpensive, and just use a wire wrapped around one of the spark plug wires. Maybe a quick search of eBay for them as I believe less than 40 dollars each. I am thinking of doing that because I have looked for 2 years for an Airguide tach number 665 with no luck. The omc experts will have to jump in with info on the temperature question and even maybe a better tach option. Also maybe list these questions under the J.E.G.O. Forum. Good luck. Super nice twin rig. I sold a motor exactly like yours years ago... I probably should have kept it as I was the second owner. First owner ran it for 50 years and it was still original... the transom broke is how I got it. Cool looking motors. Yours is twice as cool!!
it's possible. you would need a temp sensor to attach to the cylinder head. Like Dr. Go said the OMC gurus would be more informational. A little button switch is just an on/off switch for a clothes dryer, should cut out about 140/150 degrees but they come in different temp ranges. Make sure the thermostat on the motor is in good working condition. If you do the modification you could Hook up a light or horn in a straight circuit and it should work. Most appliance dealers would have something.
You would have to figure out if the switch is a norm off or norm on. I think the dryer buttons are normally on and if the dryer overheats the switch opens and cuts off power. Just a guess here.
For the most accurate temperature reading, scrape to bare metal the area of the head that's in direct contact with the sensor. You could even use some conductive heat paste (like Arctic Silver CPU paste) between sensor and cyl head to make it work even better. You can also get conductive paste at any electronics store and most auto parts stores.
You'll note on the installation diagram the sensor is attached to a JohnRude BigTwin cylinder head. How 'bout that!!
Hi Bill (it's been quite awhile),
Nice picture of your gorgeous work!
Personally, I much prefer a water pressure gauge, because if monitored, loss of water pressure precludes over-heating, giving time to "save" the engine. Slightly delayed results of a electric temperature gauge (it's sensing the outside of the cylinder head) is very often "too late" (for a piston(s)). Forums are for expressing opinions, that's mine. As to gauges/instruments, a stainless steel bezel is available, versus a black or white bezel, and seems far more "in keeping" with vintage chrome bezel gauges of the past. I will comment that I do not know where the best place on a "Big Twin" OMC to drill and tap to install a hose barb fitting to then connect the water pressure gauge tubing, as I do with most any Mercury outboard (Mercury started offering a water pressure gauge about 60 years ago).
Joe, you piqued my curiosity now. A couple of questions arise.
The water pressure gauge would be a good addition but:
1. Where would you install the reader?
2. What should good pressure be?
3. Wouldn't the thermostat opening and closing effect the pressure reading?
4. If the thermostat is open wouldn't that indicate a low water pressure since the cooling water is pushing through at a faster pace?
5. On initial startup the thermostat is closed until warmup so pressure would be higher and then as the motor warms up the pressure indicator would lower.
6. High pressure could indicate either a blocked cooling passage or a closed thermostat.
7. Low pressure could indicate a bad impeller, leaking gasket, stuck thermostat etc.
8. Don't the manufacturing engineers (tongue in cheek) factor in the temp alarm so it would sound or light before there is piston or cylinder damage?
Seems like paranoia would set in each time the captain looks at the pressure gauge
Just curious. I've never thought of this angle before.
donsaulsbury wrote: The reason the link didn't work is because there is a space between www. and ebay and between ebay. and com.
Correct, you can't post a complete link here because the forum's software won't allow it. Copy the link, paste into your browser's address bar, and remove the spaces and it'll work. Or go to eBay and search for Item # 181615565632
Thanks for the responses, ( and compliments) thought I did post that in JEGO, but apparently not LOL. I have used those digital tachs in other applications, but was hoping to use period correct Airguide tachs. Thanks Ed-mc I was not aware those existed, looks like a good option. It has been awhile Joe, that is a very interesting point, one I had not considered, but makes sense, and 63 Sabre, thanks for asking all the questions, saved me a lot of typing!
I agree about wanting to use vintage correct airguide tachometer. I think only the mechanics, dealers, experts know what tachs work with what year and model motor. All of the internet searching I have done leaves me a little in the dark about what model, what module and what wiring diagram is correct for my applications. If I can’t find the right information and airguide tach info by the time I need it, I may be forced to place a non active correct airguide tach on the dash and then hide a digital tach somewhere out of general site where only the driver can see it. I really want the real thing, but just can’t find a 665 model with module and wiring guide. I would rather have a tach than a speedo so I can prop for my setup and also keep rpm’s in check if using a small ski prop. Hopefully there is an expert here that can get you that correct model you need... even better if they have a spare for sale.
That was the best source I had found in the past. I still struggle with finding my 665 model. I have other models for other motors, but I will still need to find a source about how to find the right module and what to connect it to. I wish I could find an in depth airguide manual if one exists. I am not smart enough to figure out how a tach works. Hope that chart helps others. Sorry I am not more helpful providing answers to this thread.
I have a .pdf of the installation manual for the Airguide 665, it doesn't show the module # but it does have detailed wiring diagrams. Send me a private mssg with your email address and I'll forward the info to you..........ed
Thanks. Still hoping more help comes to Barnekalbill regarding his questions for that great looking twin rig. I apologize for getting off subject. Another question regarding your twins: can they both hook to the same battery and do they both provide charge to the battery without damaging each other’s charging system? As a kid in the 60s I thought I remember adults talking about only connecting the charging systems of only one of 2 Merc 65hp twins from 1965 so that it wouldn’t burn something up. I remember them always starting one motor first and saying they did that so it would start sending charge to the battery before the second motor was started. Just curious. Twin rigs alway catch my eye no matter big or small.
I'm not familiar with dual-Merc charging issues, but the older ones are unregulated, 10 amps max. So if you had 2 charging systems connected to one battery, would it eventually boil the battery dry? I dunno, some folks have problems with that in a single-engine application! I'd say having 2 unregulated current-generating devices in parallel is just asking for trouble!
The old JohnRude BigTwins, if they have a charging system at all, would have generators. You probably wouldn't want 2 generators, with their respective voltage regulators, in parallel on one battery. Not sure if they would fight each other but I dunno if I'd take the chance of burning up those expensive DC regulators!
One generator charging a single battery for dual motors would be Plenty Good. Or, if you could stand the extra weight and both engines have generators, use separate batteries.
With a single-battery setup, you wouldn't want to start both at the same time, though, due to current draw.
Yes, both motors connect to the same battery, only one motor has the generator & voltage regulator. If they both had them, they would fight each other, I believe smoke would be involved. I do start the motor with the generator first, but doubt it makes much difference, as the generator doesn't charge very quickly like today's alternators. You can't really start both at the same time, as you have to turn the key and push the choke button at the same time, I would run out of fingers.
Thanks for the help
Great information and nice motors. After over a decade, now I might be regretting selling a one owner still running original engine, controls and tank. It was heading to Florida with several other motors from the Tomahawk National antique outboard show for full restoration. I think they like getting fresh water motors that are only used a few times a summer that don’t have salt corrosion. Maybe I should use 2 separate snowmobile batteries side by side that could fit in the same battery space. I would have to experiment with cranking amps for the 6 cylinder.
Thanks guys, the motors are getting even purtier. A buddy stopped by, said he had something for me. Opened the box to find two re manufactured bronze props that he knew I was looking for. A little buffing, and paint the retainers black and we're good to go!
Friends like that are hard to find!
Cheers, I'm still smiling