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Fuel/Oil Ratio on J-321

Victor B

Registered
Hello all,

Newby to Smokstak and thanks for allowing me in. I'm a new owner of a PU-181A/PGC-1 Genset. This is I think a Jacobsen J-321 engine and is placarded for a fuel/oil ratio of 16:1 but I need to know if running it at 40 or 50:1 will damage the engine. It just seems that 16:1 is going to generate a lot of smoke which I'd like to avoid if possible. I use one of the "perfect mixes" in all my other 2 stroke equipment and have for years with no noticeable issues but since this is a vintage engine I thought I should seek guidance. Thanks in advance,

Victor B.
 

Rich Mc

Registered
Re: Fuel/oil ratio on J-321

The engine could also be a Jacobson GE-12-F if it would make a difference? Also the 3600 rpm is slow in comparison to other 2 cycle applications, many of the ratios were determined before the EPA existed.
 

nehog

Registered
Re: Fuel/oil ratio on J-321

I'd strongly recommend using the ratio specified by the engine maker (the placard) and not trying a 'leaner' mixture. The ability to use 40 or 50:1 is more than just oil, but includes issues such as metal and manufacturing tollerences.
 

Victor B

Registered
Re: Fuel/oil ratio on J-321

I stand corrected on the engine type, it is in fact a GE-12-G. As for fuel/oil ratio, I don't think that using less oil would enrichen the mixture. I spoke with a local small engine repairman today who is of the opinion that a 40:1 or 50:1 mixture would not cause any harm. But Nehog makes a good point.

VB
 

Andrew Mackey

Moderator
Last Subscription Date
05/14/2017
Re: Fuel/oil ratio on J-321

The mixture of the gasoline is not the issue. Using a leaner oil mix will starve the bearings for lubrication, causing their early demise. You may also end up seizing the piston in the bore, for lack of lubrication. If the oil mix is specified at 16:1, then use it! Failure to do so may lead to early engine failure. The older engine does not have the hardenned metals used in todays lean oil mix engines, therefore it needs all the lube it can get. If it specifies SAE 30 NON Detergent, USE IT. The old oil sticks to surfaces better than the modern lubes, and stays in the bearings longer. It also has more body than the new lubes, which helps seal seals and other clearances. If you use a modern 2 stroke oil, make sure it is suitable for your engine. Is it air cooled or water cooled? It makes a difference. Be sure to shake the can before every refill, to prevent oil settling. Yes, it happens even with modern lubes! If your engine smokes a lot, check carb and choke stettings. Too rich a mixture may cause smoke. Are you idling the engine a lot? That will cause oil retention in the crankcase. Running the engine no load, long term, will also cause this. Are you running the engine short term (less than 15-20 minutes)? If so, the engine is probably not getting hot enough to burn off all the oil in the crankcase and the muffler. A properly set up Jacobsen will not smoke much, even one running on 8:1 ratio (early engine). Most 321 Jakes I own. will not smoke, once properly set up amd warmed up to operating temperature. I also own engines that use 12:1, which do not smoke, once warmed up. Try the 16:1, you might like it!

Andrew:D
 

Victor B

Registered
Re: Fuel/oil ratio on J-321

Thanks Andrew. I suppose metallurgy has changed a bit in the last 60 years and even though 16:1 may have been very conservative, I don't want to be a test pilot with my new little generator. It is a sweet running engine and starts very easily, one or two pulls with a short rope. It made electricity right away even without the need for a flashing of the field. I've ordered a small engines manual which the seller said covered this engine family so I will have better information for operating the Jacobsen.

Does anyone know how late into the 50's the GE-12-G was built?

Victor B.
 

Rich Mc

Registered
Re: Fuel/oil ratio on J-321

The unit was a standard Signal Corp catalog item in 1959 with a GE-12-F or -G engine. I have no later catalog available.
 

Victor B

Registered
Re: Fuel/oil ratio on J-321

Thank you, Rich. What is a good source of information on these? The web has not been good to my searches on this rig except for finding Smokstak!

Victor B
 

coyote62ny

Registered
Re: Fuel/oil ratio on J-321

if you use the leaner oil mix in this engine you will tear up the bearings 16 to 1 8 ounces sae 30 non detergent motor oil to 1 gallon of gas this engine has needle bearings on the connecting rod that will not like the leaner mix stick with what the tag says hope this helps
 

Rich Mc

Registered
Re: Fuel/oil ratio on J-321

Try to locate a copy of the Dept of the Army Technical Manual; TM 11-942. Contrary to the nay sayers I am sure that if the 2 cycle oil of today was available in the 1940's the manufacturers would specify the 50/1 ratio. The 2 cycle oil of today is a complex chemical with enhanced mixing, lubricating and wear resistant properties that have been developed over the last many decades.
 

Patrick62

Registered
Re: Fuel/oil ratio on J-321

You are mostly ok to use the newer oil mixtures.
I hang out here a lot, and we are quite a conglomeration of folks running some very old saws. http://www.arboristsite.com/

The old jacobson was designed for 30wt non-det oil, which isn't that great a 2 cycle oil hence the need to run it at 16:1
Newer oil is far superior, and can run very well at the 40 or 50 to 1 ratio.

What would I do? I would probably run that thing like my old Lawnboy which worked for years (and years, and years) at 32:1 with ashless oil. It had the needle bearings in it as well. I don't think that a jacobson is any better or worse than that OMC engine.

My 2 cents worth
 

JakeSecor

Registered
Re: Fuel/oil ratio on J-321

Being a Jacobsen mechanic from the 60's, I recall that the 321 engine could be run on a 32:1 mixture (that's why it was called the 321 engine - for 32:1). The Lawn Boy ran on 8:1 then 16:1 (I believe for the "D" series engines) so the Jacobsens ran on a leaner mixture.
 

Victor B

Registered
PU-181A metal fuel cap

Gents,
I picked up this little genset at an estate sale last week. It was seized and appeared to have been at least partially submerged. The engine is now free and with the exception of a fuel line, repairing of a hole in the tank, finding a replacement reed valve and locating a fuel cap it is ready to run!

The fuel cap is brass/bronze and about 2" in diameter with two little ears for gripping. If anyone has an idea for a source of this fuel cap I'd appreciate hearing from them. Also I need a piece of reed valve shim steel, I've seen .004 as the thickness but I have no idea where to find it. Thanks in advance!
 
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