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An Onan JB Performance Question


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  #61  
Old 08-07-2017, 08:50:07 PM
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Default Re: A JB Performance Question

Scoops, your JB sounds good. As for your frequency meter, it seems to refresh very, very rapidly giving the impression your Hz is all over the place.

Leon, to start with do a compression test on both cylinders. Recheck your point gap. Check the gap on your plugs and ensure that the plugs are not fouled and ensure they burning correctly (both spark plugs). Spark plugs can tell many stories of how the motor is running if you can read them correctly. These are simple things to do without too much effort and zero cost. If you lived with 40-50 miles I'd run over there on the weekend to assist.


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  #62  
Old 08-07-2017, 09:07:32 PM
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Default Re: A JB Performance Question

Leon, I second Jim's opinion on either replacing or rebuilding your regulator. The diaphragm can harden and maybe not be as responsive. When you blow pressure to the vent of the Garrettson, it opens the port in the regulator due to pressure on the one side of the diaphragm. That's why the engine ran rough, it got real rich fuel mixture. I have rebuilt one of the regulators but for a couple of my builds, I have just bought a new Genuine, Garrettson. The one on my JB now has the 12 volt solenoid bleeder/enrichener which mechanically pushes the diaphragm and the gas flows into the engine. The solenoid is also adjustable on its stroke to regulate the amount of flow while it is energized.
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  #63  
Old 08-07-2017, 09:30:35 PM
Leon N. Leon N. is offline
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Default Re: A JB Performance Question

Motörhead I was thinking maybe the JB was not getting enough fuel as slowly returned to normal speed. Apparently that was not the case. My original plugs were Champion H8, I believe. They were no longer available so they sold me if I recall a Japanese equivalent.

I am going to purchase a comp gage and a auto timing light. I first need to clean off the timing marks and see if the advance is working correctly. I need to get my ambition back, remove that from tin and briefly fire up the JB and check the spark advance.

Back in 1970 during my refurb, I do not recall taking the JB spark advance mechanism apart. I do recall changing the points and setting the timing statically. I hope I do not have to disassemble the spark advance mechanism, small parts, hard to see etc. What's with the small hole on the back of the breaker plate, Onan says to make sure it is clear? I do not recall ever thinking about that as an issue.
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Old 08-07-2017, 09:45:42 PM
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Default Re: A JB Performance Question

Leon, Here is a cross reference chart for the H-8. I have always liked NGK or Denso spark plugs in air cooled VW's. Major reason was that they didn't stick in the plug threads when you pulled them out 5 years later.

http://www.sparkplug-crossreference....rt/CHAMP_PN/H8

From what I saw online, the H8 is still available. NAPA auto part stores are usually good for ordering stuff that they don't usually stock.
If you weren't on the opposite side of the country, I'd come over and loan you my timing light and compression gauge. Both are US made units.
I'll ship them to you to borrow if you can't find any quality ones.
With new computer cars and no distributors, most mechanics don't have timing lights. I'm still one of the OLD Dinosaurs!
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  #65  
Old 08-07-2017, 10:03:29 PM
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Default Re: A JB Performance Question

I use NGK and nothing else. NGK threads are 1000 times better than Champion. BMW use NGK brand plugs too as well as other high end plugs.

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  #66  
Old 08-08-2017, 01:32:48 AM
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Default Re: A JB Performance Question

Leon, if you still want to use Champion spark plugs, the updated part number for the "H8" is now "H8C" stock number "587", still tha same plug, also which my 4.0 cck uses.
also a lot of auto parts stores loan tools like, auto zone, advanced auto parts, and o'reilly.


I know that this is a apples-to-oranges comparison, but i
did a load test on my "UN-type" square head gasoline 4.0 cck (converted from sisson type choke to onan type choke), at NL ~65hz and 129vac (on my gens without volt regs i like to keep my volts a bit on the high side.) anyways at "FULL-OVERLOAD" of ~5,600W (actual measured, by v*a) YES you read that right, 5,600W!!! full-overload hz was ~59hz
the load consisted of 4, 1500w space heaters ( 2 "ceramic-type" and 2 nichrome wire coil-type, both fan-forced type)

windings are protected by a 2 pole 15a square-D QO type breaker, this gen has a 120v only or 120-240v selector switch installed on it. (if you want details on it, just ask me.)
if i perform my "load-test" :-) for very long (~10min?) the qo breaker WILL trip.

Leon, tomorrow i plan on taking a video just for you, of me abusing my 4.0cck with the 5,600w load from a cold start with a very short warm-up period of 30 seconds max, (shhhhh, just don't tell the onan protection services police )
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  #67  
Old 08-08-2017, 07:01:43 AM
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Default Re: A JB Performance Question

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Originally Posted by turtmaster View Post
Leon, if you still want to use Champion spark plugs, the updated part number for the "H8" is now "H8C" stock number "587", still tha same plug, also which my 4.0 cck uses.
also a lot of auto parts stores loan tools like, auto zone, advanced auto parts, and o'reilly.


I know that this is a apples-to-oranges comparison, but i
did a load test on my "UN-type" square head gasoline 4.0 cck (converted from sisson type choke to onan type choke), at NL ~65hz and 129vac (on my gens without volt regs i like to keep my volts a bit on the high side.) anyways at "FULL-OVERLOAD" of ~5,600W (actual measured, by v*a) YES you read that right, 5,600W!!! full-overload hz was ~59hz
the load consisted of 4, 1500w space heaters ( 2 "ceramic-type" and 2 nichrome wire coil-type, both fan-forced type)

windings are protected by a 2 pole 15a square-D QO type breaker, this gen has a 120v only or 120-240v selector switch installed on it. (if you want details on it, just ask me.)
if i perform my "load-test" :-) for very long (~10min?) the qo breaker WILL trip.

Leon, tomorrow i plan on taking a video just for you, of me abusing my 4.0cck with the 5,600w load from a cold start with a very short warm-up period of 30 seconds max, (shhhhh, just don't tell the onan protection services police )
Good idea for Leon to go to oriellys or somewhere and borrow the tools he needs I've done it before. They can probably trust him with the tools. We're all pulling for him to get that JB tuned up.
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  #68  
Old 08-08-2017, 11:24:50 AM
Leon N. Leon N. is offline
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Default Re: A JB Performance Question

The only reason I mentioned H8's is because that is what came with my JB. I Alsor found out that our local AutoZone store will loan me a compression tester for free. Not so on the timing light which I can buy from Wallmart for ~ $13. Have relatives visiting for the next couple of weeks so I will not be able to work on the JB until then. However, I am tempted to run that comp test since it is so easy to do. I got a feeling my JB timing is suspect, but that takes more doing cuz, I have to remove the front shroud and clean the timing marks. If I go that far, I intend to R&R the starter at the same time. I intend to take lots of pictures, too. Thanks for the encouragement, it really helps.
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  #69  
Old 08-08-2017, 03:52:27 PM
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Default Re: A JB Performance Question

Leon.
That hole on the timing assembly is to let oil in to lubricate the shaft for the points advance mechanism.
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Old 08-20-2017, 05:19:12 PM
Leon N. Leon N. is offline
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Default Re: A JB Performance Question

It was a nice afternoon here today so I decided to run a dry compression test on my JB. To do this I purchased a new compression gage for just under $10. I could not find my old one I used back in 1970 when I refurbished my JB.

Well the results surprised me to say the least because I was expecting numbers like I recorded back in 1970 that is 90 & 88 PSI.

Well I measured 145 and 140 in the two cylinders. If this new gage is accurate and truth full, that explains why I can get rated output and then some on natural gas.

Can someone refresh my mind and tell me how from the factory build sheet, for example, one can tell if his JB is a Hi or lo comp design?

I always thought my JB was of the lo comp design. Were all those JB's with a comb carb were lo comp engines?

Next step when I get a chance is to check the "running" timing. That will take some doing because I have to make visible the flywheel timing marks.
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Old 08-20-2017, 05:23:12 PM
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Default Re: A JB Performance Question

Leon, was there a lot of oil type carbon build up in the cylinders? Does your JB use oil excluding leaks?

What brand compression gauge are you using? A $10 or less gauge tells me it is cheap-azz p.o.s. CHINESE made.

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  #72  
Old 08-20-2017, 06:26:38 PM
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Default Re: A JB Performance Question

As far as I recall, no one has found the published compression pressure for the 9.2:1 engines.

And no one has written anything here on load banking a NG fueled JB set to see what it's capable of.

A gasoline (low compression) JB will make 10 kW. That same set on natural gas (after advancing the spark timing) maxes out at ~7.8 kW.

I've always been curious what a high CR JB makes. (I'm not particularly curious about guesses - I want to see real measurements )

That said, Leon - something is/was out of wack if your CR increased over the last 47 years. That or you got a bunch of crud in the heads...

Anybody have the build sheet for Leon's set? Did they even make high CR sets back then?
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  #73  
Old 08-20-2017, 06:35:50 PM
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Default Re: A JB Performance Question

MyJB does not use any significant amount of oil. Yes there are some oil leaks. In fact there was some oil in the #1 plug well. not much but a little puddle from a leaking valve cover gasket. The plugs are very very clean.

The gage is called a amity AC stem compression gage. The instruction sheet says it was from the Lincoln Industrial Corporation, St. Louis, MO. The form was printed in Taiwan

At this point I do not know for sure what the comp ratio really is. How does one tell without tearing the unit apart? That I do not intend to do at this point. IMhave no reason to think there is a carbon build up because it never has used any significant amount of oil. IN fact back in 1978 it ran 24/7'for several days and was down ally about 1/2 quart.

What I did learn,is the difference in readings between the two,cylinders is well,within the Onan recommended tolerance of 10 PSI.

Prior to the dry comp,test, I ran the JB for 20 minutes to,get it fully warmed up. It ran very smooth, not carb popping but it still groaned when dumped with a 4 KW load, but recovered nicely after about 2-3 seconds. Oh well. My next test is to,check the timing. If that is also OK, then I will focus on the Garretson which is about 50 years old.
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Old 08-20-2017, 07:19:03 PM
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Default Re: A JB Performance Question

Quote:
Originally Posted by Leon N. View Post
...At this point I do not know for sure what the comp ratio really is. How does one tell without tearing the unit apart?
Build sheet?

Cylinderoscopy down the spark plug hole?
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  #75  
Old 08-20-2017, 07:40:37 PM
Leon N. Leon N. is offline
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Default Re: A JB Performance Question

Jim I do not have the equipment to look down the spark plug hole. BTW, I like the higher compression if that is a true reading. I do not know which readings to believe?

I recall replacing all 4 valve guides and one intake valve. Never touched anything else way back then.

But where and how does one determine their machines CR???

The Onan major over haul manual merely specs gasoline-only and gaseous fueled plants BUT ITS SAYS NOTHING ABOUT PLANTS THAT HAVE TR-FUELED CARBURETORS!

On page 44 in 967-500, talks about the compression of a "standard new engine" (what ever that means) as having a pressure about 110 PSI.

My original readings were 90 & 87 now they are 145 & 140.
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Old 08-20-2017, 08:36:59 PM
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Default Re: A JB Performance Question

Quote:
Originally Posted by Leon N. View Post
Jim I do not have the equipment to look down the spark plug hole. BTW, I like the higher compression if that is a true reading. I do not know which readings to believe?

---- snip ----
On page 44 in 967-500, talks about the compression of a "standard new engine" (what ever that means) as having a pressure about 110 PSI.

My original readings were 90 & 87 now they are 145 & 140.
Leon, before refurbing my JB, I had compression readings of 130 and 140 p.s.i. using a Snap On compression gauge (see attached picture below). Upon further investigation I found that the cylinder head and the crown the pistons had oil carbon build up because the JB was not broken in properly (got it with 216 hours on the clock). All the deposits were cleaned up and the heads redone with new valve stem seals and a simple valve job, not that the valves needed it...

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  #77  
Old 08-20-2017, 08:49:52 PM
len k len k is offline
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Default Re: A JB Performance Question

Would think the accuracy of a $10 gauge is questionable. I cross check gauges against gauge on my DeVilbiss variable pressure regulator ( for paint spraying ). Seems pretty accurate, it always has compared well to good gauges I test with it. Rubber tire valve stems are convenient for sealing to gauges sometimes.

Advanced auto parts loans out tools free, just put down the cost of the tool as a deposit.
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Old 08-20-2017, 08:54:49 PM
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Default Re: A JB Performance Question

... continuation from my last post.

Leon, I attached several more pictures below showing the build up after only 216 hours of use on natural gas for a set not properly broken in.

In the first picture below, I show the before and after cleaning of the JB's head. The before picture looks a little nasty for only 216 hours.

The second picture show the before and after cleaning on the pistons.

In the last picture, you can clearly see that the cross hatching honing that looks factory new.

the sum it up, I believe that my high compression readings were caused by the oil carbon deposits on the head and pistons. Since your readings were ~90 about a billion years ago, and now are 140-145, I wonder what is going on under the head of your JB...

JohnnyC
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  #79  
Old 08-20-2017, 09:19:18 PM
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Default Re: A JB Performance Question

I remember Leon rebuilt his JB many years ago. Maybe it got broken in and it seals better now?
Would guess on nat gas won't be much carbon.
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Old 08-20-2017, 09:26:33 PM
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Default Re: A JB Performance Question

Leon post model and serial numbers and I will check build sheet. I would also go to AutoZone or some other major Auto parts store and borrow a compression gauge for free. Just give them a deposit. Compare the readings between both gauges.
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