Jump to content

Locked up cub motor. Don't know why.


J-Madd

Recommended Posts

Jetting was ok according to the plug chop I did, but it locked up anyway. I was going down a gravel road halling ass 6th gear WOT, but I'd let out every 3 seconds or so and get back in it. I let out to take a curve and went back on the gas and it locked up. this happened to me on my other Cub motor over a year ago and I called it a cold seize, but this motor was warm and I'd went 3 miles or so when this happened. (172 mains in 39 mm pwks, temp 45, alt 300ft)

 

I haven't tore the top end apart, but I know what I'll see. What are my options here. You can't just bore and hone these cylinders can you? If that was the case, I'd have this fixed in a couple days with a fresh bore and pistons.

 

Please advise!!!!

Link to comment
Share on other sites

  • Replies 36
  • Created
  • Last Reply

Top Posters In This Topic

well as long as it didnt tear the nikasil up you can just throw new pistons and rings in it. just grab whatever size pistons it takes and go..

 

 

It had to tear it up to lock up a cylinder, right? (at least the other motor did)

 

How thick is the nikasil? Is it possible to hone out the scratches, or bore it at all it the scratches are very deep (which I'm sure they are.)

Edited by J-Madd
Link to comment
Share on other sites

Normally, you can just hone the nikasil to take off the glaze.

But it's a crap shoot/guesing game right now...

 

Take off the top end, see what it looks like. don't forget, locking up an engine is not nice on the crank/crank bearings, either...

 

 

This is a brand new crank/bearings. This sucks.

 

Any idea why this would happen in the first place? Is it not safe to hold it WFO for a few seconds then let out and get back in the throttle? That's how I've alway ran down long straight roads, even on 4-pokes.

Link to comment
Share on other sites

This is a brand new crank/bearings. This sucks.

 

Any idea why this would happen in the first place? Is it not safe to hold it WFO for a few seconds then let out and get back in the throttle? That's how I've alway ran down long straight roads, even on 4-pokes.

 

I wouldn't ride it for a LONG time at WOT in 6th, but...it should run at WOT for a little while like you're saying without locking up.

Might be time to check the taper/bore of the cylinders...etc.

 

Did you check it for clearances, squish, compression...etc.

Running good enough fuel and oil, etc.?

Link to comment
Share on other sites

I wouldn't ride it for a LONG time at WOT in 6th, but...it should run at WOT for a little while like you're saying without locking up.

Might be time to check the taper/bore of the cylinders...etc.

 

Did you check it for clearances, squish, compression...etc.

Running good enough fuel and oil, etc.?

 

 

Ring clearance was within tolerance, squish was 0.045", compression 180 psi running 108 octane Klotz fuel at 32:1 with super techniplate. These are (were) brand new cylinders.

Edited by J-Madd
Link to comment
Share on other sites

Well for it to happen to you twice you are doing something wrong. Are you sure both carbs are clean and not leaning out one side or the other...............?

 

 

Different carbs were on the other locked up motor. Running a stock gas line on one carb, and a tad bigger line on the other both times, though, if that matters. I don't see the bowls running dry, with burping the throttle every 3 seconds or so, but I'm open to anything to not let this happen again. This was not the first time today that I'd halled ass a few miles, 3 seconds at a time, but it was a little cooler outside when it locked. I tried to post a pic of my plug chop before I rode today,but the file was too big. It was tan with at least 2mm band.

Link to comment
Share on other sites

I have a pingel. Surely I couldn't have sucked the bowls dry. But if that's what happend I'm done riding this thing on long roads. I'll stick to drag racing instead of riding down long roads, but it was fun going 90+ on gravel.

 

Edit: I thought the pingel was listed in my sig, but it's not.

Edited by J-Madd
Link to comment
Share on other sites

I have a pingel. Surely I couldn't have sucked the bowls dry. But if that's what happend I'm done riding this thing on long roads. I'll stick to drag racing instead of riding down long roads, but it was fun going 90+ on gravel.

 

Edit: I thought the pingel was listed in my sig, but it's not.

 

The other part of the equation way have to to with you gas cap. The stock caps and some of the cheaper aftermarket caps do not relieve the negative pressure fast enough and thus limit the vlow of gas out of the tank. :thumbsup:

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

×
×
  • Create New...