Service bulletin for improving Robin engine starting

[Marks481]

I never saw this one, but it is interesting:

http://www.jackssmallengines.com/pdf_documents/robin engines/Manuals/RA-SB-015.pdf

It says that the Robin engine may be difficult to start because of parasitic loads such as hydraulic pumps in cold weather. Sounds kind of familiar.

It recommends swapping out the oem starter motor for the heavy duty version that Faztrac is currently looking at replacing on another thread.

It also swaps out spark plugs and starter coils. It says it applies to 2002 models, but I suspect that the later models might also have the weaker "HD" starter motor and ignition coils.

 

[Gravy]

I never saw this one, but it is interesting:

http://www.jackssmallengines.com/pdf_documents/robin engines/Manuals/RA-SB-015.pdf

It says that the Robin engine may be difficult to start because of parasitic loads such as hydraulic pumps in cold weather. Sounds kind of familiar.

It recommends swapping out the oem starter motor for the heavy duty version that Faztrac is currently looking at replacing on another thread.

It also swaps out spark plugs and starter coils. It says it applies to 2002 models, but I suspect that the later models might also have the weaker "HD" starter motor and ignition coils.

According to JackRobin (I miss him) my 2004 came with the updated coils and spark plugs. He sent me the heavy duty starter at no charge. It helped a bit, but the difference wasn't dramatic. I wouldn't expect too much.

 

[BobRip]

I have done it on my 2000 PT422. I don't see a big difference, but my PT is stored in a heat garage.

 

[Marks481]

I will have to check the starter motor number on my 2005 model. But with Gravy'sreport that the different starter didn't make much difference, I might not bother.

I wonder how much room a clutch would take to install?

Actually, I bet the bestway to improve winter starting performance would be to figure out how to shoehorn a group 24 (full size auto battery) into the engine compartment. The little garden tractor battery just doesn't seem to have enough cold cranking amps... and it is a fairly new battery. AnytimeI needto start when it is less then 40F, I have to put the charger on it.

 

[Clumber]

Tim,

The battery that came with my new PT 425 is 2/3 size of a car battery-- should be sufficient and easier to fit. See photo.

 

[BobRip]

I put an Optima yellow top in mine. It's the same size that fits some Hondas. 450CCA. I keep it on a float charge. This will help.

 

[Gravy]

My PT425 has a Honda car size battery - maybe a Group 41 if I remember right. There is no other common automotive battery size that will fit the narrow space. I've looked at the higher tech batteries such as Optimus, but I haven't found a higher capacity battery that will drop in. I replaced the OE Chinese cheapie with a higher quality NAPA battery, but it didn't make much difference.

Heavier gauge cables might help a bit, especially if the negative cable attached directly to the starter mounting bolt.

Oddly, my tired 25hp Robin that ate a whole bunch of dust in the first year that I owned it has gotten better at cold starting in the last year. It should be dead, but it seems to be getting better.

 

[BobRip]

Heavier gauge cables might help a bit, especially if the negative cable attached directly to the starter mounting bolt.

.

My experience developing battery powered products shows that reducing losses in wires can make a big difference in operation. This is cheap and easy (I think) to do. I have not tried it though on a PT. A heavier wire tied directly to the starter bolt would be with trying.

 

[ponytug]

I agree. One of the first things that I did after getting my PT was to up the battery cable sizes, and add a central ground point on the engine, with extra ground wires to the front and to the tub itself. I also sanded the ground point on the engine for the best electrical connection. (In hindsight, I probably should have run one over to the ground screw on the the electrical interconnect, but that was before I had taken it apart.)

As always, YMMV...

All the best,

Peter

My experience developing battery powered products shows that reducing losses in wires can make a big difference in operation. This is cheap and easy (I think) to do. I have not tried it though on a PT. A heavier wire tied directly to the starter bolt would be with trying.

 

[BobRip]

I agree. One of the first things that I did after getting my PT was to up the battery cable sizes, and add a central ground point on the engine, with extra ground wires to the front and to the tub itself. I also sanded the ground point on the engine for the best electrical connection. (In hindsight, I probably should have run one over to the ground screw on the the electrical interconnect, but that was before I had taken it apart.)

As always, YMMV...

All the best,

Peter

How does your machine start below 50 deg and 40?

 

[ernemats]

My 422 which is now 12 years old starts without any problems as low as 20 degrees, at lower temperatures I might have to try it several times but it has always started and it still has the original battery and very seldom have I put it on charge.
Now my 1845 will start at the same temperature ranges but it struggles at the low temperatures and when it does start it idles very roughly for several minutes and smokes a lot.

 

[BobRip]

My 422 which is now 12 years old starts without any problems as low as 20 degrees, at lower temperatures I might have to try it several times but it has always started and it still has the original battery and very seldom have I put it on charge.
Now my 1845 will start at the same temperature ranges but it struggles at the low temperatures and when it does start it idles very roughly for several minutes and smokes a lot.

Any idea what is different about you machine? Yours is about the same age as mine.

 

[ernemats]

I have no idea. Several years after I purchased mine sometimes it was very difficult to start in cold weather, then I changed spark plugs to the ones Jack Robin suggested and that seemed to help.

 

[BobRip]

I agree. One of the first things that I did after getting my PT was to up the battery cable sizes, and add a central ground point on the engine, with extra ground wires to the front and to the tub itself. I also sanded the ground point on the engine for the best electrical connection. (In hindsight, I probably should have run one over to the ground screw on the the electrical interconnect, but that was before I had taken it apart.)

As always, YMMV...

All the best,

Peter

In order to get an idea of the losses in the battery cables I measured the voltage drop on the cables while cranking. I then calculated the resistance assuming 90 amps of cranking current. If you have a better number let me know.
Positive cable. 0.023 volts 0.00253 ohms
Negative cable. 0.018 volts 0.002 ohms
Negative cable connection to starter motor. 0.05 volts. 0.0005 ohms.

The total resistance is 0.005 ohms. This is about 4% of the starter motor resistance. The test was done with the engine warm. During cold weather and a cold engine the starter current will go much higher and the cable losses will increase. With fatter cable the losses could be cut in half. Will it help to use fatter cables? The calculations don't rule that out. I don't plan to do this, but if a cable fails, I will replace it with fatter cables.

 

[Gravy]

In order to get an idea of the losses in the battery cables I measured the voltage drop on the cables while cranking. I then calculated the resistance assuming 90 amps of cranking current. If you have a better number let me know.
Positive cable. 0.023 volts 0.00253 ohms
Negative cable. 0.018 volts 0.002 ohms
Negative cable connection to starter motor. 0.05 volts. 0.0005 ohms.

The total resistance is 0.005 ohms. This is about 4% of the starter motor resistance. The test was done with the engine warm. During cold weather and a cold engine the starter current will go much higher and the cable losses will increase. With fatter cable the losses could be cut in half. Will it help to use fatter cables? The calculations don't rule that out. I don't plan to do this, but if a cable fails, I will replace it with fatter cables.

.02V isn't much voltage drop at all in a starter circuit. On mine, I would expect at least .2V and up to 2.0V in really cold weather when the starter is really working hard.

 

[BobRip]

.02V isn't much voltage drop at all in a starter circuit. On mine, I would expect at least .2V and up to 2.0V in really cold weather when the starter is really working hard.

This is just across the wires. The battery voltage will drop as you stated. My experience is that you do the math, but the actual affect is much greater than calculated. We are getting into strange territory. Edison stated that whenever you talk about batteries you are lying. What I think that means is that batteries are too complex in their behavior to describe that behavior and be completely accurate. I have found this statement to be accurate, but I am probably lying.

 

[ponytug]

Well, it is a 1445, and it starts fine at 40. 35 is getting a bit slow, but it always starts on the first crank. The thick oil in the hydraulic pumps is clearly the issue for the starter. Nonetheless, a glow plug is on my list. I can check the cable size; I think they are 2ga.

I try to let the machine warm up the hydraulic oil before trying to do much; I'm not wild about having any cavitation in the intake oil filter from the tank.

All the best,

Peter

How does your machine start below 50 deg and 40?

 

[ponytug]

Dear Bob,

It is always great to have real numbers! With those sorts of resistance numbers, any gain at all might be solely in the contact resistance at the cable ends. Yet another reason to take them apart every so often and clean them.

As I said, I did it preemptively, not because I had a problem, but because it had been a common problem for me on other engines. It might be one of those chromed under hood items- looks nice, but not functional...

Thanks again for measuring!

All the best,

Peter

In order to get an idea of the losses in the battery cables I measured the voltage drop on the cables while cranking. I then calculated the resistance assuming 90 amps of cranking current. If you have a better number let me know.
Positive cable. 0.023 volts 0.00253 ohms
Negative cable. 0.018 volts 0.002 ohms
Negative cable connection to starter motor. 0.05 volts. 0.0005 ohms.

The total resistance is 0.005 ohms. This is about 4% of the starter motor resistance. The test was done with the engine warm. During cold weather and a cold engine the starter current will go much higher and the cable losses will increase. With fatter cable the losses could be cut in half. Will it help to use fatter cables? The calculations don't rule that out. I don't plan to do this, but if a cable fails, I will replace it with fatter cables.