View Full Version : sticking pistons

Tom Lovejoy
07-07-2008, 11:58 PM
I've got a 25 Indian scout, which I finally got running awhile ago. The engine was rebuilt almost 20 years ago. I was riding it around, trying to brake it in nice and easy. It started sticking the pistons when it got hot. Let it cool and it starts right up and sounds new, but take off down the road and get it hot and it wants to lock up. I pulled the cylinders and they showed alittle scaring also on the pistons. Had 3 thousandths clearance + oil rings. Pistons were out of an old Hercules engine I was told.
I have increased the clearance to 6 thousandths and I was also advised to not put an oil control ring on the front cylinder, just run the compresion rings 2. Wondering what your thoughts are on this suggestion? its total loss oil system. What is your experiences ? thanks Tom.

07-08-2008, 07:49 AM
Hi there, I'd have a few thoughts about this...although without being the owner/rider makes it a guessing game. I'll start with the oil weight/grade and pressure in the system, I've noticed over the years that some people try to run lower weight oils or multiweights in the older machines as finding straight heavy weight oils can be a hunt. The pumps weren't designed to push thinner oils. I'm curious of the pistons being from another maker for sure even though the boresize may be similiar. The Metal expansion maybe different then what your cylinders require. The idea of leaving an Oil ring out of a cyllinder is unacceptable for a cure. I wouldn't run it hot much until you can resolve the issue as you already know what can happen. This is only a guessing game from where I'm sitting. Good luck to ya, Keep ridin them... Merlin in Pa.

23JDCA 808
07-08-2008, 09:30 AM
The opinions on an old Harley site (harleyjd@yahoogroups.com) favor not using an oil ring. The J's and JD's were designed at total loss systems and the oil is used up top for those parts. ...bill

07-08-2008, 11:57 AM
Interesting, I was going to refrain from mentioning anything about a M/C I never owned. It just sounded odd to me, Does that mean the OEM Pistons for that era M/C didn't have an oil ring as well? I enjoy this forum for many reasons and this is one. Merlin in Pa.

23JDCA 808
07-08-2008, 04:06 PM
The sense was that the oil ring (scraper) technology was not very good in those days. And blue smoke meant that oil was getting to the top end; the J and JD Harleys (1916 thru 1929) had the valves up there and the extra oil tended to lubricate things. There was no other top end lubrication.

07-08-2008, 05:33 PM
Harley J owners always say, "blue smoke is good". Of coarse you won't find too many members of the Sierra Club riding J model Harleys, or pre 30's Indians and Excelsiors.

Tom Lovejoy
07-09-2008, 12:57 AM
I am using 50 wt oil, I appreciate the replys. My scout never showed any smoke, no mater how we tried adjusting the pump. Think the oil control rings were doing their job abit to good. The fellow who did the engine, is as good as I have ever known. Been at it along time, though he told me it was the oldest engine he had ever done at the time. I learned a couple years ago, my Indians dont like multi grade oils. My eyes are not what they once were, I put 10 - 30 wt oil in my SS on a trip on time and jumped on the freeway. Thought I had gotten 30 wt, untill I was going to put the bottle in the trash.
25 miles later SS seemed sluggish and got really hot, pulled over and noticed my paint was blisted on the oil tank !!, scared the heck out of me - I knew I had wrecked my engine. Parked her in the shade, drained the oil and filled with fresh straight 30wt oil. She started right up and I got back on the freeway and continued on my trip. With the light weight oil, it just seemed to froth up but not do the job. I lucked out and did not harm my engine, several thousand miles ago :-) But my paint job still has the scars from my mistake. Thanks agian for the input.
One other thing, I use 20 - 50 wt in my Henderson with no negative effects that I know of. The Henderson does not seem to mind, dont know why the difference? Have had several people tell me to run 50 wt, but the guy who built my engine said use 20 - 50 so thats what I have done, 5,000 miles in 11 years - just for info, Tom.

07-09-2008, 11:53 AM
If you have oil control rings installed, you may be accumulating too much oil in the sump, thats what happens on a friends J model fitted with them.

Steve Slocombe
07-09-2008, 12:04 PM
I can confirm the Harley VLs were not originally fitted with oil rings, and had three equal sized rings originally. I'm guessing the oil rings came with the knucklehead, certainly by 1938 when the strutted pistons were introduced.

I now use 4 thou piston clearance with the modern repro strutted pistons, and 5 thou with my racer. Check the ring gap clearance is 14 thou minimum.

Watch out for the piston material. The original iron pistons ran with about 4 thou clearance. The original solid aluminium or magnesium alloy pistons were specified at 18 thou (they must have been noisy until the engine warmed up). The 1934 unstrutted T-slot pistons were specified at one thou (yikes!) and the 1938 strutted pistons about four thou again. So the message is to be careful if you are using nos or used pistons in your bike.

Best regards,

07-09-2008, 05:48 PM
.006 is PLENTY loose enough. I set up 101's with 2 compression rings only. I have set up the ring gap as much as .035 to make one use as much oil as the pump gives it. You should see a little blue smoke all the time if it has a total loss oil system.. That's how it loses it!

07-09-2008, 06:45 PM
Piston expansion and, or, improper ring gap may also be at fault. Paps

T. Cotten
07-09-2008, 09:59 PM
It takes heat to stick a piston.
Excessive heat.
Find the source(s) of the extra heat, and you solve the problem.

I'm a poor gambler, so I always go with the odds first: evil vacuum leak strikes again.

A simple pressuretest on the intake manifold will say yea or nay, and that would at least be a variable eliminated without conjecture or chin-scratching.


07-09-2008, 11:55 PM
I agree Cotten. He has the top end off already so it would only make sense to install those rings and verify the gaps, whie it is opened up. Can't check the old ones because he either honed it out to get the .006" clearance, or he changed or resized piston. Intake leak should have been checked first. Paps

Tom Lovejoy
07-11-2008, 12:09 AM
Yep we checked for leaks - old fashioned way. Could not get any reaction when we sprayed the manifold and it idled very well. No popping or back firing, also it never locked up in the drive way, only after going down the road. Farthest ride was 40 miles and it did not lock up untill about 20 miles of the ride were covered, then it locked up three more times on the way home. If I had an intake leak, would'nt it leak all the time and show signs or effect something? It was running fine, untill then.
I pulled the cylinders, after advice from far more experience folks than me. They said 3 thousondths is to tight for total loss oil system. Thats what I am going with, but still looking for advice from those who have been there before, I will check the manifold carefully before I put it back together ,thanks Tom.

07-11-2008, 09:00 AM
Reason I mention rings all the time is.. I once had a top end rebuilt for a Beezer of mine. The shop was well recognized and I assumed all would be ok just to install the cylinder set, pistons, rings and all, without an inspection. My mistake. I fired her up. She sounded strong and good. I didn't push her at all. I took her out for a cruise. As with you, after around 20 miles, the engine started slowing down. I poured more fuel to her but she continued to slow down at rapid pace, until she completely stopped. I tryed to kick her over right away and she was super tight. I sat by the side of the road with her for about 15 minutes or so. I tryed starting her again. She fired right up and sounded great again. At first I thought she was having a rough time breaking in so I ran her like that for a week. Nothing changed. She continued with the same symptoms as the first time. Finally, I pulled the top end off of her. Cylinder bores were slightly scored. I inserted the rings into the bore to discover the gaps to be .004" to .006" when cold. Way to tight ! Paps

Tom Lovejoy
07-12-2008, 12:10 AM
very interesting Paps, thanks - that sounds just like what my scout was doing. I wish I would of checked that. I hope to have it back up by next month and Iam real interested and hopeful that I will figure out what the problem is. Thats about what I did too, I just kept trying to ride it easier and easier. But it was no go, when they lock up that its mighty hard on your nerves. Especially when you have alot of effort, or time in it.
I took it to a pro a couple of months ago, told him what was happening. He test rode it around the block and listend to it in the drive way, said it was perfect. Could not seem to get him to take it for a longer ride, as I thought it needed to get hotter. But he did not and said all was fine. So thats why I am trying to figure it out, with help from friends - thanks again Tom.

10-22-2008, 11:57 PM
Just a thought, but have you checked to see if the rods are straight? Indian rods are pretty easy to tweak a bit at the small end. The marks on the pistons from locking up would not be even, rather offset from top to bottom. Even with a lot of clearance on set up, if the piston isn't square in the bore it can start to nip up with heat. Go ahead, ask me how I know.

10-23-2008, 08:06 AM
Are you sure it's the pistons seizing? A friend of mine had the same issue years ago with a freshly rebuilt flathead and it turned out to be the flywheel thrust washer not haveing enough clearance. Ran until it got hot..then seized. Cooled down, ran until it got hot...then seized.

Just another thought.....Good luck.