seized

[harrO]

Attn: Brian Kirby  -  A couple weeks ago you stated that your bike seized every time you rode it. I'm experiencing a similar problem on my '69 Penton. It starts on first kick but quits after aprox 3 miles, acting like it has seized. Will bump start before rolling to stop. Do you recall how your bike acted and/or any other symptoms? Appreciate your response.

[brian kirby]

The bike I was talking about was a mid 80s Cagiva 125 and it seized for real, like wide open throttle then BAM almost instant hard lockup. Almost killed me a few times. If your bike has a Motoplat I would suspect that, if it still has points...donno.

Brian

[harrO]

Thanks Brian. Sounds like dissimilar problems. While cruising at 35-40 my bike suddenly looses power before locking up. I swapped  the 130 for a 134 main jet and lowered the jet needle to position 4. It accelerates much better now and runs without having to manipulate the choke but still "quits" at the 3 mile mark. I am using the conventional point ignition. Thanks again for your rapid reply...I'll keep searching!  Harry O

[thrownchain]

Sounds like the condenser to me.

[Mickey Sergeant]

What does your plug look like,Should be chocolate brown.If on the white side to lean.

[joe novak]

Be sure the gas cap is vented properly.

[tomale]

A couple things come to mind, Has a pressure test ever been done to the engine? It could be as simple as a main seal or as strange as a flaw in the casting of the cylinder.. I had a bike that had a crack in the intake casting portion of the cylinder. It was very small but it caused my bike to sieze when it warmed up.  I think that the warming up of the cylinder actually caused the crack to open even more..On another bike the cylinder was warped and it would not seat flush on the center cases causing a leak. Small bore bikes are more likely to seize than big bore bikes so getting them sealed up right is very important and these old bikes, things reveal them selves that we never would have seen when they were new. Maybe someone here can give you a ball park idea as to what size of jets you should be running. Each bike is different but you should be close to what others are running. Elevation has to be considered but not as much as you might think. One or two sizes in either larger or smaller depending on where you are. If we start with Sea level and then adjust to your situation you should be able to get pretty close. Close enough that small adjustments is more than likely all you need. Here is just an example; lets say that at Sea level your bike should be running a 175 main but you are at 2500 feet so the main should be 170.. these are not real numbers, only numbers I made up to for the sake of example..getting the main jet close is pretty eash and a pilot jet has alot of adjustment to it so it can be fiddled with but the needle jet can cause all sorts of trouble and can be hard to figure out. Take it slow and change only one thing at a time..

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
74'250 hare scrambler (project)
74' 1/2 440 maico
78' 440 maico
72' cr125 Husky (project)
93' RMx 250 suzuki

[harrO]

Thanks to all for ideas and places to look. On rebuild I was told  a head gasket was not needed. There was a gasket when I disassembled the motor however. Might this be a source of air leak as Thom suggested?  Coil and  condenser had been swapped out on round #1 of this project. Still has original main seal so I'm thinking  that should be explored also.

[OUCWBOY]

HarrO,
The Cast Iron cylinder Sachs engines were not designed for a head gasket. If yours had one, either it was a mistake or there is some sort of problem. In most cases, the proper torque on the head bolts should prevent air leakage there. Besides the seals, ensure the cylinder is fitted with a base gasket and sometimes you develop an air leak around the intake as well. Replace the two fiber gaskets inside the carb (the mounting side has a fiber sleeve and a round fiber gasket.
It it actually seizing up or is it just stopping? Also ensure you have the proper oil ratio in your pre-mix gas.

Donny Smith
Paragould, AR

[harrO]

Thanks Donny. I'm confident of the gas mix ratio...but may be a tad on the rich side. When I say seizing thats the term I've adopted because it's exactly what I would expect a seizure to feel like. It rapidly looses power and If I don't grab the clutch quick enough the engine shuts down and the rear  locks up. It will bump start before coming to a complete stop but I don't press things at this time and just gingerly limp it home. The more I talk with you guys I am suspecting an air leak of some sort...even though the plug doesn't indicate a lean burn.

[linglewn]

You mentioned that the engine had just been rebuilt. Are you sure that you have the proper piston-to-cylinder clearance? A too-tight piston will generate heat and quickly cause seizure. It pays to look for the simple things first.

Nelson Lingle
73 Jackpiner
74 Jackpiner
71 DKW 125

[OUCWBOY]

If you pull the clutch in soon enough, the engine will continue to run?? Is that what you are saying? If that is the case, it appears to be more related to the gear box vs piston seizure??!!??  Just to ensure it's not a piston seizure, pull the cylinder and see if there is any visual indication of seizing.
This is a strange one!!!

Donny Smith
Paragould, AR

[harrO]

No Donny.... The engine is not running when things lock up but it will restart by 'popping' clutch  before rolling to a complete stop. Pulling in the clutch at just the right moment keeps the back end from siding out from under me.  HO

[G Ellis]

I would pull the head and cylinder off. Check and see if piston has scuff marks. Sounds to me that piston to cylinder clearance is to tight. Later Gary

[dirtbike]

I agree. Too tight fit between piston and cylinder. There are some other strange things that can be going on as well, such as a defect piston that expands non-uniform, or a bore that is not straight, or even 2 cases from different engines that doesn't form a straigt base for the cylinder bottom, so it leans over slight and the bore isn't perpendicular to the crank shaft.