Hercules JXD oil pressure

[cessna]

I am having the exact same issue OZ had many moons ago.
viewtopic.php?f=82&t=121396

During the restoration process, we mostly ran the M-20 in the shop, pulling it out every so often, but not really running it much. Last week we got it out of the shop and took it for a trip up and down about 1/2 mile of our dirt lane a few times to make sure the brakes, clutch, transfercase etc works.
IT was then we noticed the M-20 would start and hold at 25-30 when we first started it up, but once it hit about 150 degrees it would creep down to 12-15. When we got it back into the shop, we found it sat dangerously close to 0 at idle. We changed the oil this past Sunday after another issue ( viewtopic.php?f=82&t=206060 ). While we had the oil pan off at this time, I read up on how to adjust the oil pressure and compared it to the exposed oil pump to make sure everything moved, functioned etc.
Today I installed a mechanical oil pressure gauge to the block, warmed it up then got her up and running to 1600 rpm (using a remote tach). It ran for about 10 minutes at 26 psi, then slowly started dropping off. After about 20 minutes of consistantly running at 1600 rpm it dropped down to a little less than 12. I then had my wife watch the pressure as I lowered the rpms down to idle. It crept down dangerously close to 0. I immediately shut it off so we do not inflict any damage on it.
We are running 5 1/2 quarts of SAE30 along with 1/2 qt of Marvels.
Temperature stays steady at 150 degrees.
Before we did the initial start up months ago, we turned it many times over by hand, then used the cranking motor with no juice to the coil until we had pressure built up.

Any ideas or suggestions? We do have another oil pump we could install, and have some JXD specific manuals enroute through the mail.
Thanks in advance,
Brian

[TopKick]

My M3A1 Scout Car is this way. One thing to check is if you are using the original flex oil line, some of the inner lining may be decayed and crumbling causing line blockage, be plugging up the line entirely. This will prevent the oil gage from working properly, or not at all. Since the engine is not over heating, I suspect all else is fine.

[j506]

With the pan off remove the oil pump and check the clearance between the cover plate and the pump gears
the herc engine tm will give the max clearance spec that woulb be my first check point,bearing clearance would be second
Hope this helps
john

[cessna]

THanks fellas,
we are still waiting on the JXD manuals to show up. If anyone has the specifications, and could post or email them to me, that would be great! I have a friend's baby shower in Philly today, and the old man has a family gathering to hit up. Tommorrow we will get back in the shop to get busy.
Thanks for your help,
Brian

[68427vette]

someones jxd oil pickup tube hit the crank and sheared off,, maybe that other thread??

[m8m20]

My m20 is exactly the same as this, it runs at very low oil pressure, about 10 psi. It starts of at 35 psi and as the oil gets hot it drops away. Have people had this problem alot before?

Regards

Jon

[John Neuenburg]

Mine goes up to just under 20 and stays there with very little change due to heat or rpm. Sometimes I wonder if the gage sticks there. The thing I don't like is it takes a while to see any pressure when starting from cold.

[clintm20]

I've got about 200 miles on my rebuild and it holds rock solid at 40lbs no matter what. I'd kinda suspect the rebuild is maybe not so good, especially considered the parts in the bottom of the pan you found.

[cessna]

Gentlemen,
Sorry for the long delay, we were at a pause due to another side job, and the regular work schedule...
We received the "Operation and Maintenance Manual for JX series Engines" manual, unfortunatley it is missing pages 52,53,56,and 57. These are the pages that actually talk about the oil pump with the scavenger pump, and figure 50 and 54. Kinda stinks since that is the first thing we wanted to check. Could anyone email me these pages? stingaroo499 at yahoo dot com.
We removed oil pan today and we are checking things out. I will let you know what we find out as things progress.
Thanks for your time,
Brian

[68427vette]

what kinda compression are you getting? on each cylinder?

[yogibear]

Generally speaking, if the oil pressure drops off after the engine warms it...it indicates worn mains and big end bearings....camshaft bearings also. A local guy who used to operate several trucks with the JXD engine told me...."whenever you rebuild one of these engines, ALWAYS replace the camshaft bearings, as if you do not, you won't have good oil pressure."

[John Neuenburg]

Low or no oil pressure is not funny but I have a funny story about it. Back in the 1971when I was getting into motorcycle racing my brother and I were at Laguna Seca watching the AMA national road races. The rules had recently been changed taking away the engine size advantage for flathead engines that Harley-Davidson enjoyed for years with the KR750. So with overhead valve engines allowed to go up from 500cc to 750, to compete with the British bikes Harley cobbled together a 750 V-twin with iron cylinders. It had a lot of problems. Down on power, ran hot, etc. So we were standing in the pits watching the H-D team work and Mark Brelsford coasted in on his XR750. The mechanic got to work on it and acted very pissed off. Then he said to the team manager, "It doesn't have any oil pressure!" The equally pissed off manager said, "Well put some oil pressure in it!"

[cessna]

Hey fellas, thank you for all of the comments, information and suggestions. John, that is an awesome story, I had a conversation with Erik Buell at East Troy Wisconsin in 2008, he was telling me oil pressure and overheating was his biggest problem at the beginning of his racing career.

We pulled the pan earlier this week, Dad checked all of the crank bearings. Most were .002 or .003, however one was way out and he managed to shim it back. The everything was set on the oil pump. We reassembled everything and this time used SAE40. AFter a few seconds of running it was up to 65 on the mechanical oil gauge! I immediately shut off the engine and turned down the regulator a bit. We then started it up again and warmed it up to 150 degrees at about 750-800 rpm. Pressure stayed at about 30.
Next we cranked the motor up to 1600rpms as the manual suggested. It ran steady for about 5 minutes at 1600rpms with 26-28, then backed down to a little under 20. After 15 minutes at 1600rpm, it stayed at about 17. We then set the motor down to 750rpm, oil pressure read in at about 5, motor temp raised to about 165. (it is about 96 degrees out with high humidity). No strange noises, not rattles, the motor sounded pretty darn good. We applied a bit of gas, and the oil pressure raised back up to 12-15.
We shut it off and just came in to eat lunch. Going back out, install the belly pans, and run it up and down the lane a few times, maybe visit my friend's hayfield.
We are going to work on it the rest of this weekend amongst a tune up on a Farmall Super A, and installing a rebuilt carb on a 55 Power Wagon. Hopefully my wife and I can fit in some Maryland Blue Crabs and brews
I will let you know as things turn out. Hopefully this thread can help someone else out down the road.
Brian

[John Neuenburg]

50wt oil = "can of oil pressure"

Those crabs sound good! We have dungeness crabs off of San Fran. Very yummy.

Good MVs + good food & drink = good times!

[cessna]

Gentlemen,
Latest update. We now have constant oil pressure, ran it in 100+degree heat and it did not hit 0, stayed a little bit above 8-10lbs. We did not notice any change in the engine temperature with the belly pans installed, still stayed between 150-170 degrees. I am pretty excited for Matt F. (the owner) to come down and take it for his first test drive.
I am going to try to take some pictures later today/tomorrow to show what tools you can use, and what the oil pump looks like when adjusting the oil pressure down the road.
Brian
PS John we made it out for some Maryland Blue crabs, all you can eat. Gotta say I was a little under the weather the following day haha.