Ace 100B+ piston seizure

[cineburger]

In the last episode of my ongoing Hodaka Saga you all were kind enough to contribute to my education about proper sprocket ratios and trying to resolve intermittent carb problems; your ideas helped me immensely and I thought I solved most of my issues except finding the proper gear ratio for my purposes; I was in the process of testing those about a month ago when I returned from a 20 minute test ride in about 48 degree temperatures when the bike stalled out on reaching the garage and was then unstartable. Compression was down to 48-50 lbs when it was 150 on prior readings. I seized the piston. On removal it appears to have abraded on about 80 degree of its circumference on the exhaust side; the barrel is scored beyond honing and needs to be rebored. Running fresh fuel with good synthetic oil mix at 32:1; the barrel is clean otherwise with no evidence of metal shavings or other debris causing the seizure. Bike running well during the testing in all gears with plenty of pulling strength at all levels of throttle. Any ideas as to why this seized?? Could it have been uneven head bolt torquing?? Possible improper break-in when new?? Next question--any advice as to what oversize piston I should look for?? Anybody wanna part with one?? I suspect 1 over is too thin and I should go for at least #2 over if I could find that piston....any thoughts? Thanks in advance for continuing to educate me....Happy New Year to you all, david.

[dirty_rat]

Colder temperatures will cause you bike to run leaner (as the air is denser) and if it is a significant difference from when you jetting the bike, it can lead to problems such as a piston seizure.

As for the bore condition, much of what you see in the cylinder could be aluminum from the piston. If there are no deep scrapes, the next oversize piston should clean it up. If you send the cylinder to one of the Hodaka suppliers, they should have a few pistons on hand to determine exactly which oversize piston you need and have it bored for that piston.

When racing, we have had pistons sieze up at the races. At the track we would just clean it up as best as we could and make sure the ring wasn't sticking in its groove (this is usually the cause of the poor compression readings), put it back together, make some jetting adjustments and race it in our next moto. Almost always would finish the weekend without any further problems (these engines are remarkably tough).

[Al Harpster]

I believe some photos of the piston assembly and cylinder may be helpful.

.010 over whatever you have could give a substantial clean-up.

The causes of sieze come down to just 2.

Insufficient clearance piston to cylinder.

Insufficient lubrication.

Insufficient lubrication is a little trickey because lubrication is supplied with fuel.

I think this is where Rich vs. Lean comes in.

Rich means more gasoline, and gasoline carries the lubrication.

Lean.... Well that's less of both.

I'm throwing out insufficient clearance because the engine's probably old enough to discount that.

I'll also throw out excessive heat because it's cold out and you were not participating in a race.

I'm thinking Air Leak as a likely culprit.

Have you ever pressure tested this motor?

If yes and it passed I'd check jet markings and jet needle position to specs in owners or workshop manual.

Yep, it's possible you didn't put enough oil in the gas. That's stunningly unlikely. Even if you were off by 50% modern lubricants should do for street riding even diluted.

Hope this helps..... Some

[Joe Ormonde]

I`m going to add 1 to your list Al. A Connecting Rod installed in the wrong direction. Look up (Piston Thrust Face) and you will all understand. There are 2 basic ways to cause the piston to rock towards the Intake side in a Hodaka Engine. One is to offset the Piston Pin Bore the other is to build the offset into the Connecting Rod. Hodaka built the offset into the Rod. When the fuel air mixture burns causing the piston to be forced down, the offset built into the small end of the connecting rod causes the piston to rock towards the intake side of the Cylinder. When this happens, the Piston actually has only the oil film on the Piston Intake Skirt and Cylinder: No Clearance. All the clearance is on the Exhaust side Piston Skirt. So if the Piston to cylinder clearance is lets say .004, going down the piston has Zero clearance on the intake side but .004 on the Exhaust side. Going back up the opposite happens. If you can read ACE 91 on the right side of the Crank Shaft (Clutch Side) the Crank was put together wrong and the piston will destroy itself in short order. Just another thing to check when troubleshooting a Piston problem! Joe Ormonde.

[cineburger]

As you may note the abrasion marks are all on the exhaust side of the cylinder wall; gotta think this is a strong argument for cold air cooling the cylinder before the piston; also, in response to Bullfrog's comment on another similar B+ seizure thread, the pin was quite tightened hard to remove as opposed to "thumb-pressure" snug suggesting some kind of deformity, improper manufacture, or installer error--let alone who knows what happened in the past 47 years...

[matt glascock]

Cool Joe.

[Bullfrog]

In the previous thread, didn't we talk about the possibility of air leaks?

Before you do the bore job, I'd recommend reinstalling the cylinder with a new base gasket and head gasket (with or with out piston - if without piston, be sure to wrap/pad the rod end so no damage will be done if you should forget and give the engine a spin with the kick starter). Then do a pressure test. I'll place a two-bit bet right now that it will fail the test. If there is an air leak, you'll be able to identify where it is leaking . . . and you can do the repair on the leak while the cylinder is being bored.

It is also pretty handy to just send your cylinder to someone like Terry Larson/Hodaka Dave. They will be able to access the proper piston whether it cleans up at .020" oversize or has to go to .030" oversize. In that way, you purchase only the piston which is "right" for the bore job.

Ed

[Al Harpster]

I believe the preference for fit piston pin to piston refers to assembly.

Disassembly after years of use may reasonably require additional force.

I know mine did.

I found Joe's information on piston thrust most interesting. Two questions here for Joe:

Could you post an exadurated sketch of a rod with the offset you mentioned?

How might this apply to after market connecting rods?

Back to the problem.....

The best initial approach to find cause of failure is two fold. Pressure test and re- confirm jet numbers & jet needle setting.

You might also assure the Pilot Jet and Pilot circuit are clear. This may be a bit of a long shot, but the pilot circuit is always giving fuel. No matter what throttle opening.

[cineburger]

Thanks for the suggestions fellas; Ed--yer right we did discuss the leak test in my previous thread and it has been on the back burner ever since; I thought it wasn't necessary when the bike was running so well in all gears once I got the 13t sprocket on the front, but alas current conditions have changed that!! I will try to get that done and report back...more anon--d

[matt glascock]

I used to be amazed at how well a 2-stroke bike runs seconds before detonation. Now, I'm alarmed. When all of a sudden the bike begins running instantly better that it did previously, time to consider a leak down test or, at least a quick plug check.

[Dale]

I`m going to add 1 to your list Al. A Connecting Rod installed in the wrong direction. Look up (Piston Thrust Face) and you will all understand. There are 2 basic ways to cause the piston to rock towards the Intake side in a Hodaka Engine. One is to offset the Piston Pin Bore the other is to build the offset into the Connecting Rod. Hodaka built the offset into the Rod. When the fuel air mixture burns causing the piston to be forced down, the offset built into the small end of the connecting rod causes the piston to rock towards the intake side of the Cylinder. When this happens, the Piston actually has only the oil film on the Piston Intake Skirt and Cylinder: No Clearance. All the clearance is on the Exhaust side Piston Skirt. So if the Piston to cylinder clearance is lets say .004, going down the piston has Zero clearance on the intake side but .004 on the Exhaust side. Going back up the opposite happens. If you can read ACE 91 on the right side of the Crank Shaft (Clutch Side) the Crank was put together wrong and the piston will destroy itself in short order. Just another thing to check when troubleshooting a Piston problem! Joe Ormonde.

Joe, Your statement that the Hodaka rods have an offset built into them was the first time that I have ever heard that. I have studied a NOS ACE91 rod and I can not detect any offset. Can you share more about this subject and how you determined there to be an offset?

[TheBevman]

In the previous thread, didn't we talk about the possibility of air leaks?

Before you do the bore job, I'd recommend reinstalling the cylinder with a new base gasket and head gasket (with or with out piston - if without piston, be sure to wrap/pad the rod end so no damage will be done if you should forget and give the engine a spin with the kick starter). Then do a pressure test. I'll place a two-bit bet right now that it will fail the test. If there is an air leak, you'll be able to identify where it is leaking . . . and you can do the repair on the leak while the cylinder is being bored.

Ed

I'm seconding Ed's information above. I had my '72 Wombat seize in Oct and after doing the same thing he mentioned I found that the sealant of the case joint failed just below the cylinder. I would also recommend vacuum checking the cases too, same procedure but with a vacuum gauge. My set up is a Harbor Freight vacuum gauge and HF brake bleeder to provide the suction. I aim for 6 in/Hg, with less than 1 in/Hg drop in 1 min, same as the pressure test.

My Wombat didn't run any better or worse, it just started to bog so I clutched it and it died. When I tried to start it back up... thinking it was just a fuel feed issue (had those in the past too) I found it was locked solid. It freed up after cooling and that's when I did the pressure and vacuum checks before tearing it down.

After reading all your post above, I'd venture a guess that it was either jetting related or and air/ vacuum leak.

Bev

[cineburger]

Captain Ed--I owe you a beer! never took you up on the rhetorical two-bit bet but the leak down test proved you right; it failed so miserably that I thought I might not have the openings sealed properly, but alas gotta be the inner seals methinks....here's a pic of my Eyeball Engineering tester; I can't seem to post the short test video but it never held any pressure and when pumped to 6 lbs immediately fell back down to zero. No spritzer bubbles on the exterior gasket/seal areas....teardown fun in progress.....

[MTrat]

Did you check if air was leaking out through the crankcase vent when you pressure tested it?

[Bullfrog]

I hope I'm getting back on this thread in time. It would be good to do the pressure test/soapy water check directly on the magneto side seal and the clutch side seal and all over after you get the side covers and other stuff off the engine. That way you will KNOW where the leak was. I would be awful to do a full teardown, replace bearings and seals, reassemble the engine and THEN find out you have a porous or cracked case.
Ed

[swcaudill]

Hey cineburger,
Arrived home with your cylinder and piston. Hope to start the bore job today or tomorrow.
Sterling

[cineburger]

Epilog to chapter 1 of my never-ending Hodaka saga...that is, never-ending in a good way since I figure to be preoccupied with this endeavor for a long time...2 over piston and rebored cylinder--thanks, Sterling, for the work and expert disassembly/assembly coaching--now installed and 1st (moderate, thanks Capt. Ed) test drive completed; bike runs great--much improved over all previous trial runs before seizure. Unfortunately, (it's a long story) due to circumstances within and beyond my control, the leak down test was never performed competently. The incompetence was entirely my fault and I'm still working on building a proper-sealing tester for the future.The bike is now reset to completely "normal" carb settings (middle notch on needle, 95 jet) and #8 plug and on my modest test drive after warm up it had that great 2-stroke popping sound that was missing from all other previous early test rides. Good fresh 93 octane fuel with Golden Spectro 16-1 mix. Splitting the cases was as learning experience for me and I gotta say on this bike it seemed relatively simple inside as long as everything removed was kept in an organized and documented (for a memory-challenged backyard mechanic like me) manner; nuff-said--I recommend doing this to all who enjoy this kinda activity and have some time to not-rush-it. Thanks again to all who offered encouragement and advice on this Forum which is a great wealth of information for all things Hodaka..now I gotta withstand the urge to continue testing in more frigid weather (it was 65 yesterday--30's today) and follow Bullfrog's advice on another thread about breaking-in such a rebuilt motor....PS--inside the cases was a very clean and almost "unused" transmission with no particles or debris to be found; bearings were like new; we changed the seals and put it back together properly.....bring-on the sun.....thanks again to all....david

[Bullfrog]

Cineburger,
If I have read things correctly, you still haven't completed an error free crankcase pressure test. It is wonderful that the bike is running and sounding better . . . however I take little comfort from those reports. A small air leak which is effectively larger (in proportion) at low throttle settings (such as medium speed county road cruise) could kill your engine again. You won't KNOW that you don't have a crankcase air leak until you complete a proper leak down test. I highly recommend that you call a time-out on riding and complete the pressure test using soapy water to identify where any leaks are. (and hopefully the test will prove that the engine is leak free and life will confidently be wonderful again)

On your current course of action, the first symptom of an air leak could quite easily be another piston seizure.
Ed

[cineburger]

Ed--I value and appreciate your advice and will do it. Cold weather has frozen any temptations to continue breaking-in. I will pressure test first and report back. Thanks agin.

[cineburger]

Reporting back--I finally got the leak down tester working correctly after a lengthy operator error filled day....and everything is wonderful in my personal Hodakaland....the 6 lbs pressure holds almost without any noticeable leaking at all...when the weather cooperates (5" snow tomorrow), it's break-in time; I am forever grateful for all the commentary and advice as well as Capt Ed's insistence on what he knows to be the right way -- despite my teenaged, slothful tendencies!! life is indeed wonderful agin....yeehaw