Generators and Motors
[Home] - [HELP] - [Forums] - [Library] - [Photo Gallery] - [Groups] - [Classified Ads] - [Subscribe] - [Links] - [Books] - [Sponsors] -

Go Back   SmokStak > SmokStak® Vintage Electrical Equipment > Generators & Motors General Discussion > Onan Generators
Forgot Password? Join Us!

Notices

Onan Generators Restoring, operating and maintaining vintage Onan generators.

Onan Generators

Onan 7.5JB-3CR/9804T - Welcome 'red' to the family


this thread has 105 replies and has been viewed 4316 times

Reply
 
Thread Tools Display Modes
  #61  
Old 04-10-2016, 07:34:57 PM
BStrutton BStrutton is offline
Subscriber
 
Join Date: Jan 2013
Location: Howell, Michigan
Posts: 54
Thanks: 25
Thanked 22 Times in 11 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

A few pics of the weekend's progress.

And don't make fun of my blast 'cabinet' That UHAUL 'wardrobe' box has gone 3 rounds with my 2 6.5 NH's, a bit on the JB now as well as an endless parade of Jeep parts.

It is outfitted with my 80 gallon Belaire two stage, a skat blast gun and my shopvac clears the air great. I run soda, black beauty and beads in it. Might be the best $11 bucks I ever spent!

I see great deals on fantastic cabinets all the time on craigslist but JUST don't have the room with all the other project stuff Maybe one day when I move out of suburbia and have a pole barn..
Attached Thumbnails
Click image for larger version

Name:	JB-ControlTrayBlasted.jpg
Views:	64
Size:	95.4 KB
ID:	251220   Click image for larger version

Name:	JB-ControlTrayBlastedCloseUp.jpg
Views:	55
Size:	110.2 KB
ID:	251221   Click image for larger version

Name:	JB-PTOCylinderHonedandCleaned.jpg
Views:	58
Size:	61.9 KB
ID:	251222   Click image for larger version

Name:	JB-HeadsDoneCloseUp.jpg
Views:	55
Size:	152.8 KB
ID:	251223  

Reply With Quote
Sponsored Links
  #62  
Old 04-10-2016, 07:40:33 PM
BStrutton BStrutton is offline
Subscriber
 
Join Date: Jan 2013
Location: Howell, Michigan
Posts: 54
Thanks: 25
Thanked 22 Times in 11 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

More weekend fun..

Gave the head gasket a good dose of permatex copper sealer. If this set proves out I'm gonna go through the whole thing & will replace the gasket then but didn't want to spend money & wait on parts until I see if it will fire & produce.
Attached Thumbnails
Click image for larger version

Name:	JB-HeadGasketCopperCoatedforTesting.jpg
Views:	43
Size:	158.9 KB
ID:	251224   Click image for larger version

Name:	ExhaustManifoldRusted.jpg
Views:	46
Size:	111.0 KB
ID:	251225  
Reply With Quote
  #63  
Old 04-10-2016, 08:49:39 PM
Motorhead's Avatar
Motorhead Motorhead is offline
Subscriber
 
Join Date: May 2007
Location: Central Coast, California
Posts: 3,133
Thanks: 1,349
Thanked 1,973 Times in 1,083 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

BStrutton, Are you cranking the engine with the plugs out?
Did you inspect the bottom of the oil pan to see if it was full of oil/water gunk? If the pan has thick gunk in it, that could be blocking the oil pump pickup. It will take some time to fill an empty oil filter at cranking speed. I would suggest you remove the oil gauge and crank the engine and see if you get oil flow. The small line that goes to the head is small. With thick cold oil, it could again take time to flow through the line at cranking speed.
Cold cranking compression isn't that much lower than hot. 15-20 psi less.
Reply With Quote
The Following User Says Thank You to Motorhead For This Post:
  #64  
Old 04-10-2016, 09:05:53 PM
BStrutton BStrutton is offline
Subscriber
 
Join Date: Jan 2013
Location: Howell, Michigan
Posts: 54
Thanks: 25
Thanked 22 Times in 11 Posts
Talking Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

Well I guess I just needed to take a break from the garage & get some grub. After the break I went back out to investigate. Spun the new filter off partway to see if it was getting anything and it was.. Unfortunately mixed with a heavy dose of fuel. I have the fuel shut off so I guess it was from what was left in the sightglass that I forgot to empty or maybe some left over after the oil change??

Anyhow, put the filter back on and on the advice of Max did put a bit of oil in the cylinders just in case.. Cranked it for about 5 seconds and the gauge came alive and simultaneously got a gusher out of the passage in top of the head. Was hitting 30 PSI on the gauge.

So tomorrow will probably compression test and put B+ to the coil to see if she'll fire & make juice.

Unfortunately the tank somehow managed to spring a pinhole leak whilst being balanced on the front rail & had to rig it with some 'JB' weld as it's all I had on hand -and fitting I reckon

Thanks again for the suggestions. This truly is a great place!

Last edited by BStrutton; 04-10-2016 at 10:23:46 PM.
Reply With Quote
  #65  
Old 04-11-2016, 07:30:19 AM
Max Thompson Max Thompson is offline
Sponsor
 
Join Date: May 2009
Location: N.W. Missouri, USA
Posts: 5,663
Thanks: 4,880
Thanked 5,177 Times in 2,842 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

Quote:
Originally Posted by BStrutton View Post
Unfortunately mixed with a heavy dose of fuel. I have the fuel shut off so I guess it was from what was left in the sightglass that I forgot to empty or maybe some left over after the oil change??
Are you using the OEM mechanical fuel pump? The diaphragms in these can leak fuel into the block. Check this before trying to start the set. If fuel did get into the oil, I would change it again before proceeding. At this stage I would be using cheep 20 or 30 weight oil with the intention of changing it to better quality when you get things going your way.
Reply With Quote
The Following 2 Users Say Thank You to Max Thompson For This Post:
  #66  
Old 04-11-2016, 05:11:22 PM
BStrutton BStrutton is offline
Subscriber
 
Join Date: Jan 2013
Location: Howell, Michigan
Posts: 54
Thanks: 25
Thanked 22 Times in 11 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

Yep Max it was still on the mechanical filter. And yep I always start off unknowns with the cheapest possible wally world dino crude so no biggie to dump 3.5 qts, drain the new filter & start over before firing it. Might pre-fill the filter this time so don't have to crank as long..

I've pulled the mechanical pump and the diaphragm looks pretty done. For my testing, I've 'borrowed' the electric pump from the NH and will give it a go.

Long term I might try to find somewhere to redo the diaphragm or that can give advice on a suitable substitution as surely that design is common to more than just onan.. A search turned up an antique car forum recommending the folks at then-now-auto.com as a very good possibility. I think I could source the material & cut to fit but I honestly don't see how the darn thing comes off.. Think maybe it's referred to as 'sweged' on..
Attached Thumbnails
Click image for larger version

Name:	JB-FuelPumpDisassembled.jpg
Views:	45
Size:	119.9 KB
ID:	251316  
Reply With Quote
  #67  
Old 04-11-2016, 05:46:20 PM
Max Thompson Max Thompson is offline
Sponsor
 
Join Date: May 2009
Location: N.W. Missouri, USA
Posts: 5,663
Thanks: 4,880
Thanked 5,177 Times in 2,842 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

You are correct, that pump is common to most gasoline or diesel fueled J series sets (which is a bunch). For what a good Facet elec. pump costs & the risk of damage that could result from fuel diluted oil, I would not mess with the mechanical pump.
Reply With Quote
The Following User Says Thank You to Max Thompson For This Post:
  #68  
Old 04-11-2016, 07:11:40 PM
Motorhead's Avatar
Motorhead Motorhead is offline
Subscriber
 
Join Date: May 2007
Location: Central Coast, California
Posts: 3,133
Thanks: 1,349
Thanked 1,973 Times in 1,083 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

Quote:
Originally Posted by BStrutton View Post
Yep Max it was still on the mechanical filter. And yep I always start off unknowns with the cheapest possible wally world dino crude so no biggie to dump 3.5 qts, drain the new filter & start over before firing it. Might pre-fill the filter this time so don't have to crank as long..

I've pulled the mechanical pump and the diaphragm looks pretty done. For my testing, I've 'borrowed' the electric pump from the NH and will give it a go.

Long term I might try to find somewhere to redo the diaphragm or that can give advice on a suitable substitution as surely that design is common to more than just onan.. A search turned up an antique car forum recommending the folks at then-now-auto.com as a very good possibility. I think I could source the material & cut to fit but I honestly don't see how the darn thing comes off.. Think maybe it's referred to as 'sweged' on..
Save everything from the old pump. There are places that restore fuel pumps by making new diaphragms. Check ebay as the complete mechanical fuel pumps come up from time to time.
Reply With Quote
  #69  
Old 04-11-2016, 09:17:44 PM
BStrutton BStrutton is offline
Subscriber
 
Join Date: Jan 2013
Location: Howell, Michigan
Posts: 54
Thanks: 25
Thanked 22 Times in 11 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

It's A L I V E ! Well, kinda

Changed out the oil & filter again. Hooked up the electric pump off of one of my NH sets & hose down into a 1 gallon can. Right now I'm just jumpering the starter & makeshift B+ to the coil and electric pump.

Cranked it and she fired right off. Half not expecting it to work right away it startled me and I pulled the B+ to shut it down.

Then it wouldn't start back. Crank, no start or sometimes starts for few seconds & backfire through air intake. Now not even getting that..

Thought maybe flooded. Pulled plugs & they look ok -not drowned.

Verified spark on both plugs. Checked compression & looks like 100-ish on the flywheel side & 85-90 on the PTO side, which was the rusty cylinder that I cleaned up & ran light hone.

I verified also that there is at least fuel in the bowl on the carb.

So seem to have fuel, air, spark, compression but no run.

I did do a minimal cleaning on the carb over the weekend didn't seem like much to mess up there but maybe ?

In my idiotic state of surprise I didn't get a good run or a great look at my meter before I pulled the B+ but it's definitely making some power -seems like I saw a figure just south of 200 volts.

After the removal of the mech pump, the oil change & it's brief run, the oil on the dipstick looks much better. This one's definitely a candidate for a couple of MMO / oil change flushes back to back.

Definitely hope for the thing I think! Suggestions on the carb / start / backfire issue appreciated.
Reply With Quote
  #70  
Old 04-11-2016, 11:03:31 PM
Motorhead's Avatar
Motorhead Motorhead is offline
Subscriber
 
Join Date: May 2007
Location: Central Coast, California
Posts: 3,133
Thanks: 1,349
Thanked 1,973 Times in 1,083 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

BE CAREFUL...You have a 6 volt ignition coil and they are expensive to replace. So make sure you are going through the resistor.
Good to hear it is running for all you have had to do. Check to see if the oil pressure switch isn't fouled up and keeping you from getting spark.
Reply With Quote
  #71  
Old 04-12-2016, 12:07:36 AM
BStrutton BStrutton is offline
Subscriber
 
Join Date: Jan 2013
Location: Howell, Michigan
Posts: 54
Thanks: 25
Thanked 22 Times in 11 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

@Motorhead,

Thanks so much for the caution. I KNEW from reading here that the start disconnect relay coil was 6v but no idea the ign coil is 6v. I was getting spark at my last test so hope it's not damaged.. The control box is completely dismantled so the oil pressure switch is out of the picture so can't be the cause currently.

What would be the correct value if a guy wanted to pick up a resistor to use to pull things down to 6v prior to reinstalling the control box?

Thanks!
Reply With Quote
  #72  
Old 04-12-2016, 01:03:30 AM
Motorhead's Avatar
Motorhead Motorhead is offline
Subscriber
 
Join Date: May 2007
Location: Central Coast, California
Posts: 3,133
Thanks: 1,349
Thanked 1,973 Times in 1,083 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

The ignition resistor, if I am not mistaken, is mounted on the same area the coil is mounted. It is mounted right next to the governor arm.

Look at POST #10 on this thread http://www.smokstak.com/forum/showthread.php?t=151159
Reply With Quote
  #73  
Old 04-12-2016, 02:20:24 AM
Ray Lynch Ray Lynch is offline
Subscriber
 
Join Date: Aug 2014
Location: New Windsor, New York, USA
Posts: 396
Thanks: 290
Thanked 241 Times in 159 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

Quote:
Originally Posted by Motorhead View Post
Save everything from the old pump. There are places that restore fuel pumps by making new diaphragms. Check ebay as the complete mechanical fuel pumps come up from time to time.
2 pumps presently on ebay. NOS for $219. Used one for $65.
Ray
Reply With Quote
The Following User Says Thank You to Ray Lynch For This Post:
  #74  
Old 04-12-2016, 12:36:45 PM
Motorhead's Avatar
Motorhead Motorhead is offline
Subscriber
 
Join Date: May 2007
Location: Central Coast, California
Posts: 3,133
Thanks: 1,349
Thanked 1,973 Times in 1,083 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

This one says it never had gasoline through it although it cycled when the generator ran on vapor fuel: http://www.ebay.com/itm/Onan-7-5jb-f...UAAOSwB4NWwQBW

This seller will work with you on a fair offer. http://www.ebay.com/itm/149-0914-JB-...EAAOxy4dNS3HmZ
Reply With Quote
The Following User Says Thank You to Motorhead For This Post:
  #75  
Old 04-15-2016, 05:01:29 PM
BStrutton BStrutton is offline
Subscriber
 
Join Date: Jan 2013
Location: Howell, Michigan
Posts: 54
Thanks: 25
Thanked 22 Times in 11 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

Please help me better understand ignition.

Still trying to get this fired again after it's brief start. I'm not that young but I think maybe JUST young enough that I don't have a good grasp on points / coil ignition systems so can use some advise here before I destroy something or tear my remaining hair out..

Control box is out for refurb. Trying to ghetto crank this to verify power output.

Thanks to Motorhead I now understand that the coil is 6v stepped down from 12 by resistor. So here's what I have:

1) Jumper cables B+ to starter and negative to chassis

2) B+ currently from other end of jumper cable to elec fuel pump and going to TOP of resistor located on right hand side of unit above the points. I measured the resistor above the points at 1.72 which I believe is correct. Am I right in that the top of this resistor is the correct place to apply 12 volts for stepping down?

The centrifugal switch gap was WAY out of spec (way big). Set it per manual.

When I crank now the points gap is throwing huge sparks and even some smoke. I can see from the extreme sparking that the points are pitted.

What am I missing here? I thought maybe condenser but replaced with a working one from my NH & same massive sparking.

I want to verify the timing but the manual procedure with genset stopped is confusing me. I disconnected the leads at the points, hooked up my fluke on audible continuity and rotate the flywheel 100% but never get tone to start with, so no break at correct spot. I think I'm realizing that those leads I disconnected were for the centrifugal switch, not points but not sure now exactly what to hook to on the points for the procedure the manual outlines..

967-0500 page 29 & 30 regarding setting the gap goes back & forth between "55 degrees" and "5 degrees" ATDC. I've scoured, cleaned & scored more my flywheel and see NO indication of 55 degrees and that doesn't make sense to me anyway. Is the whole section supposed to reference 5 degrees and the 55 is a mis-print? While very faint, my flywheel seems to have 3 marks which are virtually impossible to make out outside of the white marks even after cleaning & wire brushing. To me it appears to be TDC, 5 10 & 15 ATDC as the right-most one really appears to say 15. I've attached a pic to illustrate the spacing.

Appreciate any tips on better understanding / verifying this ignition system.
Attached Thumbnails
Click image for larger version

Name:	JB-FlywheelMarks.jpg
Views:	28
Size:	123.9 KB
ID:	251565  

Last edited by BStrutton; 04-15-2016 at 05:37:52 PM.
Reply With Quote
  #76  
Old 04-15-2016, 08:51:22 PM
nothingbutdarts nothingbutdarts is online now
Sponsor
 
Join Date: Apr 2014
Location: Bailey, Colorado, USA
Posts: 1,955
Thanks: 4,343
Thanked 838 Times in 569 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

OK, maybe I can help a little.
On page 29 of my JB manual of the same number as yours it says NOTE: Some early plants had no 55deg. mark on the flywheel. On these models. open the breaker box and rotate the flywheel until the breaker points reach maximum gap, that is where you set the .020".

As far as what I do to bypass all the electronice and jump my JB to start it. On the bottom stud of the coil I disconnect the one wire that goes back to the control box, the other wire on this stud is the condensor, leave it attached. (on my JB the coil high tension two outputs with the plug wires in them stick straight up) the studs (+ and -) point towards the breaker box. The top stud would be the - stud and the bottom stud is the + stud.
I would then take out both spark plugs, leave the plug wires attached and I have another set of jumper cables I use to ground both spark plugs. I connect on end of the cables to a good ground on the engine block and the other end of the cables to the hex of the plugs. Then I would turn the flywheel to where the points are closed, hook up a jumper wire from the battery + to the bottom stud on the coil, then use your finger or tahe a screwdriver and open the points. The plugs should both fire! This way I know the coil high tension and low voltage sides are working.
Hope this helps some.
Reply With Quote
The Following 2 Users Say Thank You to nothingbutdarts For This Post:
  #77  
Old 04-15-2016, 09:28:54 PM
Leon N. Leon N. is online now
Registered-III
 
Join Date: Oct 2009
Location: N. Chelmsford, MA, USA
Posts: 3,222
Thanks: 594
Thanked 1,867 Times in 1,110 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

Hello BStrutton:

I read your latest input with consternation when you say the following:

When I crank now the points gap is throwing huge sparks and even some smoke. You also indicate: Control box is out for refurb. Trying to ghetto crank this to verify power output.

You are obviously doing something very very wrong to see huge sparks and even smoke!

I know the folks are trying to help you but you have a wiring error with those observations.

I would not try to run the machine by Gerry rigging the wiring in lieu of the complete control box first being in place. Something is not right WRT your wiring. Also use an ohm meter to make sure your breaker point condenser is not shorted and is a 0.3 mfd condenser. The ohm meter should indicate at least 100K ohm across the condenser. 967-500 has all the information you need to set the engine-stopped timing.
Reply With Quote
  #78  
Old 04-15-2016, 10:07:04 PM
BStrutton BStrutton is offline
Subscriber
 
Join Date: Jan 2013
Location: Howell, Michigan
Posts: 54
Thanks: 25
Thanked 22 Times in 11 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

Thanks Leon I will check those values. Can you answer a specific question that I have of which resistor is responsible for reducing the voltage to the coil from 12v to 6v? Is it one of the two control box resistors (15 or 1 ohm) the 1.72 ohm 'ignition' resistor. Another post led me to believe that it was the 1.72 labeled 'ignition resistor' on the wiring diagram (the one above the points) but I'm questioning whether that's right given my current results. Looking at the diagram it almost looks like 12v flows in the control box to one of those 2 resistors that convert it to 6v and out to the positive coil terminal.

Thanks again for the advice & concern. Indeed if I can't get a clear understanding of where the 6v conversion occurs (and witness it with my meter) then I'll have to reassemble the control box which I'm not wanting to do right now for several reasons..
Reply With Quote
  #79  
Old 04-15-2016, 11:12:01 PM
nothingbutdarts nothingbutdarts is online now
Sponsor
 
Join Date: Apr 2014
Location: Bailey, Colorado, USA
Posts: 1,955
Thanks: 4,343
Thanked 838 Times in 569 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

As I mentioned above you need to hook your jumper wire to the stud I pointed out above. You get the voltage drop to the coil by the fact the coil and the resistor above the points box are in "series". It will show 12 volts both at the coil + and at the resistor when the circuit is open, when the points and close the circuit I believe there is almost an equal voltage drop between the coil and the resistor so 6 volts is being dropped at the coil and 6 volts is being dropped at the resistor.
Reply With Quote
  #80  
Old 04-15-2016, 11:19:15 PM
Vanman Vanman is offline
Subscriber
 
Join Date: Aug 2011
Location: Mission Viejo, California
Posts: 3,013
Thanks: 3,653
Thanked 1,243 Times in 844 Posts
Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

Big sparks and smoke from the points tends to make me think that somehow battery voltage was directly across them? In which case they may no longer be any good.

Keith
Reply With Quote
The Following User Says Thank You to Vanman For This Post:
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not 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 Off

F o r u m Jump

Similar Threads Chosen at Random
Thread Thread Starter F o r u m Replies Last Post
Family Hercules Smoke Antique Gas Engine Discussion 8 09-01-2014 09:43:01 PM
New member of the family Nevr-Enuf-Stuf Small Air Cooled Gasoline Engines 6 04-30-2012 12:54:35 PM
New addition to the family Steam Pig Garden Tractors / Mowers / Scooters 9 09-11-2008 09:55:54 PM
From our family to yours Steve B Antique Gas Engine Discussion 2 12-23-2007 03:57:05 AM


Use "Ctrl" mouse wheel to change screen size.
All times are GMT -4. The time now is 05:09:48 PM.

Smokstak and Enginads site search!


All use is subject to our TERMS OF SERVICE
SMOKSTAK® is a Registered Trade Mark - A Community of Antique Engine Enthusiasts
Copyright © 2000 - 2016 by Harry Matthews P.O. Box 5612 - Sarasota, FL 34277