Merc Clamshell Thermal electrickery?

9D280 · 21 January 2010, 10:52

As the rebuild is about to start, I am thinking now would be a good time to add some thermal monitoring to the engine. (And yes, I know about the "relative merits of water pressure" arguments before the thread grows legs & goes off at a tangent....)

So, I have two locations of interest - one is a recess on the starboard side near the top cylinder that I believe was used for the optional extra temp gauge, and so in theory I should be able to fnd a kit of parts for one of them and bolt it straight in, using the spare grey wire to drive the gauge. My question, as I have little spare space for a temp gauge on the console, is does anyone have an overheat switch in there? (and if so, what's it's part number so I don't end up with a "WOT alarm", or the first I know is when it siezes.....)

Secondly, there is a tapped blind hole by the top cylinder's spark plug. It's mean to be there, as the surrounding water jacket cover is cast to avoid it. Does anyone have any interesting instrumentation fixed in here? It strikes me as a far better place to monitor temp, as it's right on the top of the cylinder. I suispect it might be there to fix a piston locating detector for setting up the spark advance, but as a thermal monitoring spot, it can't be too bad.

So, Clamshell owners, can any of you shed any light on either the threaded hole, or the avaiability of a suitable thermal switch for the starboard side?

davej · 21 January 2010, 20:13

The top threaded hole near the plug is for connecting the water pressure gauge into, I bought a pressure gauge kit a few years ago from west marine in the states and had it sent here along with a few other items. It was very reasonable and fitted easily as it came with all sorts of adapters for various O/Bs, West Marine had a really good Int'l sales dept.

I have thought about fitting a Temp Gauge but never really got around to it and touch wood, at the moment my 1988 merc 60hp is a great engine, as its light and simple, never really want to change it. I premix now, as I took off the autoblend because I felt it was getting long in the tooth. I readily admit its smokey and I guess a little thirsty but its an exceptional day when it uses more than 5 or 6 gallons.

What sort of rebuild are you doing?

Good Luck

9D280 · 22 January 2010, 09:20

Dave,

Thanks for that. I'm,m not sure we are talking about the same threaded hole tho'. There is one really near the telltale outlet at the top with a brass blanking plug, the one I was talking about is right beside the plug on the back of the engine- it's an open blind hole, I guess about 3/8" thread running parallel to the spark plug thread.

Like you say, they are super light for the HP. (Only 10Kg heavier than my old Suz 25!) Mine had already been "de autoblended" when I got it, so also running premix. Form what I ather the main problem with them seemed to be the low level alarm running out of battery power. If I got one free I thought about modifying it to run off the main battery & also add a Suzi oil flow sensor for obvious reasons.... Thing is, it's not a variable mix device, so might as well save some weight & reduce the number of things to break down. If I'm doing dinghy rescue boat stop - start type stuff I usually just switch off when not moving.

Total rebuild- the replacement pistons are still en route with the shipper! (the spark advance locknut let go last year and the stop screw wound fully out during a few mins at idle, resulting in a ridiculous amount of spark advance. Fortunately (?) the shards of aluminium that came off the corner of the pistons when I drove off shorted the plugs and stopped the engine before too much internal destruction occurred. Still needed a +0.030" bore tho'. Suffice to say the locknut is going to be heatshrinked in place this time.

Taking the chance to retro fit a PT while it's a kit of parts as well, but that's another story.......

davej · 23 January 2010, 17:36

Hi,

I have just been completing some service items on the 60 merc and had a close look at the hole to the right of the top plug, its the standard thermal overheat sensor that the engines came fitted with from merc. I think its connectd to the control box buzzer, which will sound if that part of the head gets too hot, I would think yours should have it fitted.

You sound like you have certainly got your hands full doing the re build, where did you buy the bits from, the uk or usa?

Do you use iboats forum for info as I find it very useful.

cheers

9D280 · 25 January 2010, 10:20

Dave,

Nope, nothing in there (and looking at the threads, nothing ever been in there) Having found out what I have (both here, Iboats & talking to people) I think I may have an earlier model than my cowl livery might imply (and having nearly lost it twice removing it in a wind I can see why!) The throttle / gear cable clamp would imply it's an early version.

Bits coming form all over. Some lumps for the upgrade are from scrap engines (e.g the knackered throt / gear cable clip now won't need 3 tie wraps to hold it together!) Cyls now bored, and pisons en route, so the rebuild will happen soon-ish. My thoughts were that I could either trade it in (& get next to nothing for it) and potentially buy another dog, or rebuild it, spend the same money, & get a light engine of known history.