Tohatsu 40d Compression and Tacho Problems

J

joe_classic

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Hi all, I'm sure this should be in the forums but cannot find it.

I'm looking at buying a second hand Tohatsu 40D. Can anyone tell me what compression pressure I should get on a Nov 2000 Tohatsu 40D. I tested and got 100-105-100 PSI on cylinders 1-2-3. The local dealer in Australia reckons I should be getting 150PSI and has told me this motor with 100PSI is shot. Maybe the compression ratio has changed over the years for this motor. I am getting conflicting figures as I look around the web.

Any help with the official factory spec would be appreciated.

Also this same motor has a Tacho problem - everything on the motor seems fine but the seller has noted tacho does not work after he caused a short in the wiring with a screwdriver. Apparently the one 20A fuse inside the CDI cover box blew and the motor would not start after the short. He replaced the fuse, then the engine would start, but no tacho. I know its not much to go on but whats the chances he has blown something in the engine CPU/control box that had disrupted the tacho or is it more likely the tacho itself. All wiring seems to be in order. What I am afraid of is that there may e other hidden electrical failures apart from the tacho like no overheat buzzer, no oil alarms, disruption to maybe timing advance (if electronic) etc. All a bit of an unknown in a second hand motor.

BTW - seller is asking 50% of new price - is this reasonable for this motors age - it does appear reasonably well cared for apart from the faults above.

Many thanks for any help.
 
pvanv

pvanv

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Re: Tohatsu 40d Compression and Tacho Problems

Factory spec is 804 KPa (kilopascals) which is about 116 psi. The test must be made at wot with all 3 plugs out, on a warm motor. Be advised: gauges vary from one to another... a lot. You want to be within 5% for great, more than 10% is time for new rings.

The tach is the yellow and white wires, and is an alternator-triggered unit. Is it charging? The rectified may have blown in the debacle. Spark advance is internal to the CD, so if it is running, the advance is likely OK. The other sensors are the "ground out to sound" type, so they should have survived a blown fuse.

Price sounds a little high, at least for the northeast US, where that motor is considered obsolete. (Not ancient, but technologically obsolete) :)

Just my $0.02.
 
JB

JB

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Re: Tohatsu 40d Compression and Tacho Problems

I think your compression is acceptable.

Three cylinders do not go bad by the same amount at the same time. Dealers and techs are infamous for declaring usable motors as "worn out" or "shot". They need to make a living and declaring an even slightly marginal engine as okay denies them work. We see several of those a week.

A decarb might bring them up a bit, but I suspect, like pvanv, that the discrepancy is from your gauge or technique.

I would not think a 12 year old outboard is old. Tohatsus are world famous for reliability and working life.
 
TOHATSU GURU

TOHATSU GURU

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Re: Tohatsu 40d Compression and Tacho Problems

Book value is extremely low on an outboard that old due to the way they paper depreciate them. Actual value for any 50 in the US is around $1500.00 regardless of brand or year...Until it gets to be really old and then it becomes a static display.
 
J

joe_classic

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Re: Tohatsu 40d Compression and Tacho Problems

Hey guys thanks for all your good answers - the forum is great - been follwing since 2010 but is my first post.

I did actually forget to do the test at WOT but did have all 3 plugs out. The guage reads about 5 PSI low when I compared to another guage when I got home. I guess this could explain the discrepancy - how much would not testing at WOT likely to affect ??? - could be enough to bring this engines reading back into spec !!.

On the electronics I will do a voltage check on the battery to try and check the rectifier - I guess I should see an alternator output of 13.8 to 14v at battery and at moderate revs - or at least an indication that the alternator is attempting to charge checking for voltage rise after strating - YES ??

Is the oil injection electronic or mechanical - I am concerned with this electrical fault that he could have oil starved the motor (if electronic) and someway associated with a tach or some electronic signal to inject the oil. He did also raise a doubt if the low oil warning light was working on the tach as well which was a concern he even mentioned it.

Note the dealer has quoted me $390 (AUD) about the same as US dollars for a new tach - seems excessive - can I use an aftermarket tach ??

BTW - the motor running out of the water seems very responsive and smooth but I know that does not prove everything just an observation.

Anyway thanks all for your responses so far and any further tips

Cheers Joe
 
pvanv

pvanv

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Re: Tohatsu 40d Compression and Tacho Problems

Your compression seems OK. It would be nicer if all 3 cylinders were even -- which is ideal, but a slight variation is OK. Don't sweat the exact psi, as a lot of factors (including throttle plate position) can affect that. You are at 100+, and difference is within 5%, so not bad at all.

If you monitor the battery at rest, then crank, start, and run at fast idle, you should see the battery voltage dip while cranking, and then pop back up above the "rest" voltage to indicate charging. Yes, maybe 14v or so.

The oiling system is mechanical, and extremely reliable.

Aftermarket tachs can be problematic. A new Factory tach is Part # 3AC726400M, MSRP is $77.96. Has oil warning light (BLACK face, also available in white). 4 inch diameter. Manufactured by Faria Instruments exclusively for Tohatsu. Gauge has a chrome bezel and is back-lit for easy viewing at night/dusk. Features a domed lens to minimize glare in direct sunlight and a fog & scratch resistant coating. Fits all 4-stroke models and 40/50/60/70/90 2-stroke models with oil injection systems and TLDI "F" (tiller) models. Available from any dealer, including me. Your dealer may be pricing out a different unit, and/or may be adding in installation costs, but his price seems high.
 
J

joe_classic

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Mar 12, 2010
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Re: Tohatsu 40d Compression and Tacho Problems

Thanks Paul.

I have more info - got the seller of the 40D to check voltage. Prior to start the votage is arond 12.5 but raises to 14 voilt on his GPS/Nav when running so doesbn't look like rectifier is gone. It maybe that the tacho unit suffered in the short circuit he previously had.

Price for Tacho in AUST. is AUD$390 from one dealer and AUD$370 from another and that is supply only. That price is around the same in US dollars - ie $370to390 USD. ie someone is playing with me or the Australian agent (not the dealers) is just damn greedy.

You can PM me with your contact details to purchase if you like assuming you can ship to Australia. - it would have to be cheaper.

Cheers Joe
 
pvanv

pvanv

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Re: Tohatsu 40d Compression and Tacho Problems

Yes, we ship worldwide. It is a while before you get the shipment, and freight is sometimes more than the product, but we can and do sell everywhere from the US to Holland, Peru, Uzbekistan... wherever the local dealers can't or won't service the customers well.

You can drop me an email at the office: paul@obersheimersails.com, and let me know what you need, and I'll be happy to help.

I would, however, diagnose the old tach first. Just in case it's still good, and you have a wiring flaw somewhere.
 
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