Caterpillar 3208 10 rpm difference between engines

[Krawdad]

Hello all, I really hope someone can give me some ideas here. I have a reasonable working knowledge of gas engines but know absolutely nothing about diesels. I have twin Cat 3208 turbo engines and one engine idles 10 rpm faster than the other. ( I forget what the actual rpm of both is but there is a 10 rpm difference). As I advance the throttles I can get the engines to synchronize manually by ear but one throttle ends up quite a bit further advanced than the other. If I engage the Glendenning synchronizer the engines revert to being 10 rpm out.

Anybody have any ideas? How do you control the idle speed of a diesel?

Thanks for any ideas you may have.

[motion30]

Do you me 10rpm or a 1000rpm ?

[ranger58sb]

Analog tachs? Or digital with electronics control and so forth?

If analog, could just be the tach adjustments... and a difference of only 10 RPMs wouldn't be all that bad...

-Chris

[Cheechako]

10rpm? R U Kidding?

[Krawdad]

My apologies, I meant a 100 rpm difference. 700 rpm idle starboard and 800 rpm idle port. As I recall, but I may be wrong, this difference was also noted at wide open throttle.

This problem prevents the syncronizer from working properly and has been written up by the last two surveyors but no one has been able to fix it.

Chris, these are not cable driven tachs so I assume they are early electronic models.

[motion30]

I would swap the tachs side to side and see what happens

[ranger58sb]

Might be useful to compare your tach readings with an optical tach gun at the flywheel...

In any case, if they're electronic I'd guess they get their signal from software at the engine... so maybe the programming -- or the effects of the program -- on one engine is slightly different (e.g., fuel injection rate, or some such).

Or even the length of throttle cable (if you have those) might be slightly different.

Just guessing, though...

-Chris

[Krawdad]

Thanks guys! I think this system is far more complicated than I thought. I found some info on the Sams Marine forum which indicates that there are cable drives from the Cats to the Glendenning sync and then Sun Tach sending units on the Glendenning Sync connect to the tachs. Obviously my problem must be in this system somewhere.

Anybody know anything about these systems?

Can anyone tell me how idle is achieved on a diesel?

[Sailmonkey]

An idle adjustment screw will be located near the throttle arm on the fuel pump. Not like a gas engine where you need to worry about opening the egr port when advancing the throttle.

[S/V Antares]

If the Glendening unit is one of their mechanical syncs it will have drive cables coming out of the Tacho drive just above the front pulley on the 3208. They go to the shoe box looking syncro box.

If the syncro is engauged both engines will be at the same rpm regardless of what the tachs say. It is a direct mechanical connection between the two engine throttle cables. The senders for the tachs are usually pulse type producing a wave form (Square or Sinewave) They are usually located on the "Shoe Box" sync unit.

There might be an adjustment on the backside of the tachs. Run one engine up to about 1500 rpm using a photo tach and calibrate the tach if possible. Then engauge the syncro and bring up the rpm and adjust the other to match.

Idle rpm depends on throttle stop position. With the syncro on it should balance.

Analog Tachs (The ones with pointers) are typically less accurate at the beginning and end of the range (Idle and full throttle) due to a penomenon called Historisis.

I would not wory about tacho readings under 1000 rpm. It just does not matter. If the engines are synced and the tachs are off it is the tachs.

[S/V Antares]

If the engine idle rpm on the "Master" side engine is lower,.... the syncro will try to pull the "Slave down to that same rpm. If the throttle stop prevents this the sync will "Pop" out of engaugement.

[Krawdad]

Thanks guys! Will, you should be a technical writer, thanks for the detailed reply. I'm still thinking the problem is not with the tachs (upper & lower bridge tachs read the same rpm) rather I think it must be in the sync mechanism because when the Glendenning is engaged the engines run out of sync, when I turn off the Syncronizer I can manually sync them by ear but the throttle levers don't line up. I also tried to sync the motors using the tachs but darned if I can remember what the outcome was. I *think* when both tachs were set to the same rpm the the motors ran in sync.

[Sailmonkey]

Have you followed through this trouble shooting guide?

http://www.glendinningprods.com/gmp/...hooting.v1.pdf

[S/V Antares]

Krawdad, If the Glendening Sync is engaged,... the engines Simply cannot be out of sync. Trust me on this as I have worked with this system for 30 + years.

Hylas Glendening, one of my heros in life, invented this system 40+ years ago and his sons Paul and John continue his legacy with the original Sync and many new great products.

There is a direct mechanical connection between each engine with the system engaged. ...It works ...or it does not.. No in between. Cannot happen. End of story.

First thing is get a photo tach and fiddle around with it. You can get one under $100 tese days. Fix your issue... then use it to impress your friends.

[S/V Antares]

Woops! forgot to mention ..... check your ears !LOL

seriously... sound can be decieving. Anyway the Cat 3208 has only one take off for rpm. It is the output above the crank pully. It is an extension of the cam shaft so it is 1/2 speed of the crank. so when you get or borrow a photo tach you will put the reflective tape on the Crankshaft pully which is 1/1 and should match the tach (or not) Believe me when I say that instruments are not accurate at the low or high RPM. The accuracy is in the middle of the scale where it actually matters. I worked 20 years with one of the bigest insturment mfg. on the planet.