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6.5 tach drive and oil question

blazinzuk

blazinzuk

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So the 93 I am pulling the 6.5 out of for my 86 has a tach. Factory tach. What drives it? I have a tach cluster for the 86 and would like it to work.

Also getting tons of blue/gray smoke at startup. The oil is over full by probably a quart or so. Could that cause the smoke? It diminishes as it gets warmer but if you blip the throttle it gives a puff of the blue/gray smoke but it is just a puff
 
The alternator provides the tach signal on the white wire.

A little smoke isn't too big a deal as long as it isn't using a lot of oil and it clears up when warm.
 
bigblock72 said:
The alternator provides the tach signal on the white wire.

A little smoke isn't too big a deal as long as it isn't using a lot of oil and it clears up when warm.
Click to expand...

Well it's still in the donor truck and the trans is toast. So can't really tell. Hoping it's fine

It smokes less as it gets warmer. Almost disappearing when the engine is up to temp
 
Blue is engine oil. A little bit at start-up is OK - it settles down past the valve seals.

Since you can't drive it, look for blowby at idle:
After the engine is up to temp (and still running), pull off the oil filler neck cap.

ALL these engines have some blowby (and therefore a little smoke is OK), and will puff some smoke out the oil filler or dipstick tube. The amount of puffing is proportional to the amount of piston ring wear (and therefore oil usage).

Too much:

New Rebuilt Engine:
 
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One of the reasons I am not too worried about it Keith. Not much smoke out the valve cover holes or oil fill.

Also the motor hadn't been started in 3 years. Fired right off. So thinking some valve seals might be in order.

So the white wire for the tach. Will it work with the older cluster? I pulled the tach out of a c 60 it is for a gas motor but still only goes to 5 grand. Might try to find a diesel c 60 I think they o ly go to 3500

This is the tach has a 3 wire hookup on the back

 
blazinzuk said:
So the white wire for the tach. Will it work with the older cluster? I pulled the tach out of a c 60 it is for a gas motor but still only goes to 5 grand. Might try to find a diesel c 60 I think they o ly go to 3500
Click to expand...
It will not work as a direct hookup. The pulse counting and DC wave forms are different between the two (i.e.: factory GM diesel and gasser tachs expect different inputs).

You could either build a conversion circuit or buy one like this one from Dakota Digital to use the other hardware you have in hand:
http://www.dakotadigital.com/index....t_id=128/category_id=358/mode=prod/prd128.htm
 
Cool. If I were to find a diesel tach it still might be a different signal I would imagine. Guess I need to do some medium duty truck research
 
I've seen 6.2's that have a tach drive made into the vacuum pump..

Lousy picture,but the only google one I found..

I have no idea if the signal this tach drive makes would be "plug & play" with the dash cluster you have...maybe?..

images (59).jpg
 
The signal from those was used for transmission control and nothing else in the original function. All GM light diesels with a factory tach used the alternator.

They can be made to work - again with a bit of custom circuitry to condition the signal (it pulses at way too high a voltage at higher RPM).

However you look at it, Eric, it's either different junkyard parts than what you've got or the purchase of aftermarket solutions. It's a question of where you want to spend the money and time looking.

If you're not set on a dial tach in the OEM dash panel and just want to know RPM, I'd just buy a Tiny Tach and be done. I run one in my truck.
 
I have a circuit saved that should be able to trim the output voltage of those engine speed sensors down to what you need to operate a factory or aftermarket tach without burning it's input circuit up due to over-voltage. I'll post it here tonight.
 
I am going to use the engine speed sensor for a 4l80e that is in the oil pump drive using the above circuit. Just bought a 81 cluster for my dually. I will have to swap around a few gauges.
 
What timing... I was just about to ask if anybody knew anything about using a gas tach for a diesel. My 6.5 swap into my Suburban is near done. Hooking the tach wire on the alternator up to the gas tach from the '73 yields wildly inaccurate results. It's like 3500 rpm with the engine idling.

The Dakota Digital unit seems like an easy win, but, I would love to see what the home-brew version looks like:hack:
 
I finally found the right year cluster but it will be a while till it is together. The 6.5 is being torn down for a rebuild.
 
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