Starting Circuit Mystery (why won't my engine crank?) - SailNet Community
 20Likes
Reply
 
LinkBack Thread Tools
post #1 of 50 Old 08-15-2019 Thread Starter
Senior Member
 
Join Date: Oct 2016
Location: Lake Erie
Posts: 527
Thanks: 271
Thanked 25 Times in 25 Posts
Rep Power: 3
 
Starting Circuit Mystery (why won't my engine crank?)

This is the 1979 Westerbeke 40 diesel on my Tartan 37.

Short version of the question. Pushing the start button does nothing, but I've tested each part of the circuit individually and can't find the failed component.

Long version:
See attached simplified diagram:
Pushing the start button does not crank the starter. I've methodically tested everything:
1) If I supply power directly to terminal B on the solenoid, the engine starts ... to me, this demonstrates that both the solenoid AND the starter are working.
2) Putting a meter at either end of the wire between the solenoid and the button, I get near 0 ohms resistance
3) Putting a meter on the pushbutton, it shows infinite ohms when unpushed, and near 0 ohms when pushed
4) Putting a meter on the 12v supply to the pushbutton, I have about 13.6v, which is what I would expect.

So, it _appears_ as if all the parts of the system are working, but for some reason they aren't working together.

My best guess is that the solenoid is old enough that it's not quite working corectly. Such that the amperage that comes through the pushbutton is insufficient to close it, but when I jump to it directly there are enough amps to make it work. Is that something that happens with older solenoids or am I full of it?

I'd like a way to verify that this is the problem before I dump $40 on a replacement solenoid.

Thanks in advance for any advice.
Attached Thumbnails
StartCircuit.png  

Last edited by BillMoran; 08-15-2019 at 10:32 AM.
BillMoran is offline  
Sponsored Links
Advertisement
 
post #2 of 50 Old 08-15-2019
Senior Member
 
Skipper Jer's Avatar
 
Join Date: Aug 2008
Location: East of DC
Posts: 1,631
Thanks: 16
Thanked 58 Times in 56 Posts
Rep Power: 12
 
Re: Starting Circuit Mystery (why won't my engine crank?)

Forget Ohm for a bit. What do you have at the solenoid when the start button is pushed? If it is less than about 12.6 start cleaning contacts.
Minnewaska likes this.

Nor'sea 27
Don't re-accommodate me, Bro
And the trees are all keep equal by hatchet, axe and saw...RUSH
I invented a new word today, plagiarism.
Skipper Jer is online now  
The Following User Says Thank You to Skipper Jer For This Useful Post:
BillMoran (08-15-2019)
post #3 of 50 Old 08-15-2019 Thread Starter
Senior Member
 
Join Date: Oct 2016
Location: Lake Erie
Posts: 527
Thanks: 271
Thanked 25 Times in 25 Posts
Rep Power: 3
 
Re: Starting Circuit Mystery (why won't my engine crank?)

Quote:
Originally Posted by Skipper Jer View Post
Forget Ohm for a bit. What do you have at the solenoid when the start button is pushed? If it is less than about 12.6 start cleaning contacts.
Good point!

Unfortunately, it doesn't help any. I checked the voltage at the solenoid and I have 13.7v. All indicators are still pointing that the solenoid is the problem, except that when I powered it directly, it worked.

(Note: my original post said that I had 12.7 volts at the start button. Re-measuring this made me realize that was an error, it's actually 13.7. I'll update the original post, but no, you're not crazy, I originally said 12.7)
BillMoran is offline  
 
post #4 of 50 Old 08-15-2019
Master Mariner
 
capta's Avatar
 
Join Date: Jun 2011
Location: somewhere south of civilization
Posts: 7,145
Thanks: 137
Thanked 383 Times in 371 Posts
Rep Power: 9
 
Re: Starting Circuit Mystery (why won't my engine crank?)

Just like a car, you can turn on the headlights and they are nice and strong, but you can't start the car.
A bad connection may pass a low amperage draw, the headlights, but not a high one like a starter. Somewhere in your system, you have a bad connection. When it happened to me I just ran new wires directly from the switch to the starter and cut out the run through the key and harness. Sure I can now start the engine without the key, but I don't because I know that if I do, I might burn out a diode in the alternator.
Most often though, it is the engine ground which is at fault. A bad connection, a bad crimp on a lug, or too many wires on the same bolt. Especially on a boat in saltwater, a pinhole or cut in an out of sight place in a wire can corrode a wire enough to break the connection over time. These are particularly hard to find as they can be behind paneling or in a harness.
SanderO likes this.

"Any idiot can make a boat go; it takes a sailor to stop one." Spike Africa aboard the schooner Wanderer in Sausalito, Ca. 1964.
“Believe me, my young friend, there is nothing - absolutely nothing - half so much worth doing as simply messing about in boats.” ― Kenneth Grahame, The Wind in the Willows

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

facebook.com/svskippingstone
capta is online now  
post #5 of 50 Old 08-15-2019
Senior Member
 
Join Date: Oct 2011
Location: Nanaimo B.C.
Posts: 4,465
Thanks: 5
Thanked 138 Times in 137 Posts
Rep Power: 8
 
Re: Starting Circuit Mystery (why won't my engine crank?)

Have you actually removed lugs from bolts, mechanically cleaned all surfaces, washers and lugs' ? (Unless the alt is energized ,,by the key,, start/stop the engine by independent curcuit should not cause a diode blowing surge. Having a button in the engine area can be handy for bleeding and other testing)

Last edited by Capt Len; 08-15-2019 at 11:32 AM. Reason: addition
Capt Len is online now  
post #6 of 50 Old 08-15-2019 Thread Starter
Senior Member
 
Join Date: Oct 2016
Location: Lake Erie
Posts: 527
Thanks: 271
Thanked 25 Times in 25 Posts
Rep Power: 3
 
Re: Starting Circuit Mystery (why won't my engine crank?)

Quote:
Originally Posted by capta View Post
Just like a car, you can turn on the headlights and they are nice and strong, but you can't start the car.
A bad connection may pass a low amperage draw, the headlights, but not a high one like a starter. Somewhere in your system, you have a bad connection. When it happened to me I just ran new wires directly from the switch to the starter and cut out the run through the key and harness. Sure I can now start the engine without the key, but I don't because I know that if I do, I might burn out a diode in the alternator.
Most often though, it is the engine ground which is at fault. A bad connection, a bad crimp on a lug, or too many wires on the same bolt. Especially on a boat in saltwater, a pinhole or cut in an out of sight place in a wire can corrode a wire enough to break the connection over time. These are particularly hard to find as they can be behind paneling or in a harness.
All that makes sense.

Unfortunately, it leaves me twisting in the wind on the topic of "what is the right way to fix this? I suppose I could start by cleaning all the connections and seeing if the start button will work again. If so, that would definitely answer the question.

I'm surprised that the solenoid would need to pull enough amps for this to be an issue. I thought that the entire point of a solenoid is to use a tiny amperage to control a much larger amperage. I would expect that even a small amperage through the button would be sufficient to close the solenoid. This is one of the things I HATE about the Internet: searching for this part returns a jillion vendors who want to sell it to me, but I can't find a single spec sheet that specifies the amperage required to close the solenoid.

The "pinhole" comment is interesting/unsettling to me. These old (original) wires are untinned copper, so any intrusion is going to corrode them pretty quickly. What you're suggesting is that a nearly invisible breach in the insulation could be sufficient to cause a lot of corrosion and render the wire too resistive to be useful. Of course, under those circumstances, I'd still see full voltage at the load end, as long as I don't try to pull any serious amperage. Frustrating.
BillMoran is offline  
post #7 of 50 Old 08-15-2019
Senior Member
 
bristol299bob's Avatar
 
Join Date: Apr 2011
Location: Oriental NC
Posts: 444
Thanks: 121
Thanked 31 Times in 24 Posts
Rep Power: 9
 
Re: Starting Circuit Mystery (why won't my engine crank?)

A few tests that I'd do, in addition to what you have done:
  • Does the solenoid circuit draw amps when the button is pushed?
  • Does the starter circuit draw amps when the button is pushed?
  • What happens if you manually jump the wires at the button ("hot wire" the thing)

1977 Bristol 29.9
Surprise
Hull #5
Oriental NC
bristol299bob is online now  
post #8 of 50 Old 08-15-2019
Senior Member
 
CVAT's Avatar
 
Join Date: Apr 2012
Location: Raleigh, NC
Posts: 171
Thanks: 12
Thanked 13 Times in 13 Posts
Rep Power: 8
 
Re: Starting Circuit Mystery (why won't my engine crank?)

Seems you tested only one half the circuit, how are the returns i.e. the grounds are they clean and connected? Next what is the physical condition of all the wires in the circuit, not just the supply, corroded, clean then using the least abrasive method that gets the job done, frayed replace the wire, frayed wires cannot carry as much current. If all the wires are clean and not frayed and connected correctly, as stated above what is the the voltage at the solenoid when the button is pushed? If good it is the solenoid I don't know how many times in high school I ruined a screwdriver jumping a starter solenoid on a friends 69 Firebird, I know of two times we replaced the Craftsman screwdriver we used for it. Yeah I know tool abuse but when you get free unconditional replacements.....
turbo likes this.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Use your head for something other than a hat rest.
CVAT is online now  
post #9 of 50 Old 08-15-2019 Thread Starter
Senior Member
 
Join Date: Oct 2016
Location: Lake Erie
Posts: 527
Thanks: 271
Thanked 25 Times in 25 Posts
Rep Power: 3
 
Re: Starting Circuit Mystery (why won't my engine crank?)

Quote:
Originally Posted by Capt Len View Post
Have you actually removed lugs from bolts, mechanically cleaned all surfaces, washers and lugs' ? (Unless the alt is energized ,,by the key,, start/stop the engine by independent curcuit should not cause a diode blowing surge. Having a button in the engine area can be handy for bleeding and other testing)
I haven't done any cleaning so far, as (until this discussion) I didn't seriously consider corroded contacts to be a possible cause. Because (a) they don't _look_ that corroded and (b) I was assuming the amperage required to trigger the solenoid was low enough that a bit of corrosion wasn't going to make much difference.

If that's not the case, then cleaning the contacts is probably a good thing to try.

A little internet searching suggests using vinegar+salt to remove the corrosion, then neutralize the acid with baking soda. This sounds like a better idea than trying to sand everything. Thoughts?
BillMoran is offline  
post #10 of 50 Old 08-15-2019 Thread Starter
Senior Member
 
Join Date: Oct 2016
Location: Lake Erie
Posts: 527
Thanks: 271
Thanked 25 Times in 25 Posts
Rep Power: 3
 
Re: Starting Circuit Mystery (why won't my engine crank?)

Quote:
Originally Posted by bristol299bob View Post
A few tests that I'd do, in addition to what you have done:
  • Does the solenoid circuit draw amps when the button is pushed?
  • Does the starter circuit draw amps when the button is pushed?
  • What happens if you manually jump the wires at the button ("hot wire" the thing)
Testing the amp draw on the solenoid and the starter is tough to do without help, so I haven't managed to do that yet.

When I manually jump the wire at the button, the result is the same as if I pushed the button (i.e. nothing happens)
BillMoran is offline  
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now



In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.


User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome