JD Overheating

[charlieg]

Greetings everyone,
I posted this on the yahoo group page, but would appreciate input from the AMCA community.
I'm looking for some insight into a problem I've been chasing. I've got a '25 JD with Comp Dist pistons, oversize exhaust valves, new intake valves and guides, PEEK seals on the manifold, Bosch mag. After a break-in period, I had a severe overheating problem caused by an intake leak. The engine didn't seize, it just stopped running. I installed the PEEK seals and bubble tested the intake tract to check for leaks and all is good. The timing is right on. Now, the rear cylinder runs almost 100 degrees hotter than the front. Could I have galled the piston skirt on the rear cylinder. The bike starts easily, idles well, but the temperature (400 on rear, 300 on front) don't seem right to me. What do you think?
Thanks,
Charlie

[shelbyinparadise]

There are quite a few good people on this forum that will help. From my personal point of view I would want to know if there was any damage to piston shirt that a little polishing would cure than risk farther damage. A lean motor can just stop as piston starts to get tight, before it get any real damage to piston or cylinder wall.

Just my opinion I would want to be sure there was no internal problems, rather risk more damage since you say the timing, oiling and other issues are correct. Shelby

[Steve Swan]

Thank you Shelby, for your comments Would really appreciate hearing more on this topic. I'm following over at jdyahoo.

Ceramic coating piston domes, moly coating piston skirts was mentioned as a good thing.

I'm building, then restoring a 1927 JD. While i won't do Cannonball distances, i do plan on riding it and want to know i did everything i could to help this old motorcycle have a good life.

Would really appreciate hearing more on this topic.

[shelbyinparadise]

Hello Steve, As you might know the Carson team and the Cherokee Chapter fielded I think 10 to 12 JD's and a couple of Vl's most of which finished with little problems with the motors, with properly maintained adjustments. On the open road, the most important issue was how to maintain the proper amount of oil in motor, Brent Mayfield and others had it down to a science.

Ceramic coating will allow for higher temperatures and Moly coating will allow tighter clearance, But controlling the reasons for overheating in the first place is the first line of defense to stop a problem as it develops. We had intake packing nuts with peak or brass seals both back off after several thousand miles, so there is no substitute for making sure everything is tight.

Jon Neuman of Sagebrush Cycles, and Brent Mayfield of Ohio built several quality motors that endured the challenge, as well as Peter Reeves who refurbished his own motor. Shelby

[Steve Swan]

Thank you Shelby, for your reply.

I certainly do appreciate your comments, "controlling reasons for overheating in the first place."

Jon bored, fitted .005" Venolia's to my cylinders and rebuilt them. I have a couple questions for him, but want to leave him alone, considering the tragedy he, you and others have had to endure post Cannonball.

Tom Cotten did a gorgeous job rebuilding my DLX38. And, i am planning to use PEEK seals.

I've read and reread the Rider's Handbook. And the Motorcycle Repaiman's manual. So i can be as familiar as i can when working on this old man and when the day comes for his first start. I'm doing as much of the work as my accommodations allow me to do. Otherwise, i send out the remainder to those better equipped with knowledge and equipment to do the job.

You mentioned Brent Mayfield (i don't know him or Peter Reeves) having the proper amount of oil down to a science. It would really be great if i could learn more about oiling.

[shelbyinparadise]

I am meeting Jon for lunch tomorrow, I will have him contact you, Shelby

[Steve Slocombe]

I'd expect the rear cylinder to run cooler as it usually gets more oil thrown up by the flywheels, so something is not right. Oiling set-up is of course important, and the Cannonball riders should have good advice. I've seen engines built too tight as well, which is hardly surprising. Harley advised 18 thousandths clearance for the magnesium pistons, about 1 thou for the 1934 T-slot pistons, and maybe 3 or 4 for the 1938 strutted pistons. I'm using 5-6 thousandths for the Eastern Parts replicas of the 1938 strutted skirt pistons which most of us use these days, and the bikes run noticeably cooler.

[tfburke3]

Greetings everyone,
I posted this on the yahoo group page, but would appreciate input from the AMCA community.
I'm looking for some insight into a problem I've been chasing. I've got a '25 JD with Comp Dist pistons, oversize exhaust valves, new intake valves and guides, PEEK seals on the manifold, Bosch mag. After a break-in period, I had a severe overheating problem caused by an intake leak. The engine didn't seize, it just stopped running. I installed the PEEK seals and bubble tested the intake tract to check for leaks and all is good. The timing is right on. Now, the rear cylinder runs almost 100 degrees hotter than the front. Could I have galled the piston skirt on the rear cylinder. The bike starts easily, idles well, but the temperature (400 on rear, 300 on front) don't seem right to me. What do you think?
Thanks,
Charlie

I think if the troubleshooting overheating I would measure exhaust gas temp with a gun at beginning of header.If large diff in temps right after start up ,much higher on overheating cylinder ,I would lean towards timing,valve or ignition,and fuel mixture.If egt is ok then I think friction is the issue and internal inspection required.
Tom

[NUMO]

Hi Steve,

I will call you this week to discuss your overheating problems.

[Steve Swan]

Steve, please post what you learn from Jon. Thanks in advance !

[Jerry Wieland]

Seldom see a rear piston scored from lack of oil or overheat. Usually J's score the back side of the front cylinder. I think .005" is a little tight using Competition Pistons. Mine at .006" scored. Jerry