Piston hitting head I think?? Engine knocking badly and keeps cracking the head.

[johnsoma]

Can I just change the bearing on the top of the rod connected to the piston? Does that one typically go bad? How much is it? If that goes bad you're saying it will allow my piston to travel (when running) higher in the cylinder bc of its force and thus hit the head and crack it?

Once I remove the piston pin does the piston just lift off? Then what? Is it a pin that I can just knock out with a screwdriver then order another one online and push in there?

 

[Greg58]

Look at all the pictures in Normans post, it shows everything. But you still haven't answered my question, are you using a torque wrench to tighten the head?

 

[johnsoma]

I am using a torque wrench.

 

[johnsoma]

I looked at normans post but it doesn't show what happens after you pull the pin?

 

[johnsoma]

He says that you pull the pin and then the piston comes off, do I have to knock out a "Wrist pin first" How do I do that?

He goes from pull the pin like pulling teeth to the wrist pin being out and not describing how to get the pin out. DO I bang it out with a screwdriver?

Is the wrist pin a needle bering that you are referring to that could have gone bad? Or are they two different parts?

 

[Greg58]

I know all this sounds confusing but its not that hard. First after looking at your pictures the crack looks like a stress crack, kinda like the head was not tightened evenly. My inch pound torque wrench is a 1/4 inch drive, most are. What is yours? Is it a inch pound or a foot pound? If using a foot pound wrench adjust it to ten foot pounds. Not knocking you, just trying to cover everything.

 

[2door]

You have yet to answer the basic question. Is there evidence on the top of the piston that it is hitting the head? If it hit the head hard enough to break it there will be obvious signs of metal to metal contact. If there is none then you have other issues, maybe a warped cylinder. If the gasket sealing surface of the cylinder isn't exactly flat then that could draw the head down incorrectly causing it to crack. Where did you get the replacement cylinder head?

Use the search feature and look up, 'lapping' to see what it is and how to do it. But first answer the question about piston to head contact. Also, did you ever have this engine apart? Did you ever remove both the cylinder and the head ?

Just a word of caution. Be careful turning the engine over without the head installed. The cylinder is not held in place without the head and if it comes loose you can do serious damage to the piston, rod, rings, etc. if the cylinder comes off and the piston comes out of the cylinder while the crankshaft is rotating.

Tom

 

[johnsoma]

I had mine tightened from a local mechanic using his torque wrench as I unfort. yet don't own one. Need one for sure.

Uneven tightening could explain the second head failure but what about the first one when it was reassembled from the factory. I didnt do anything to it other than mount it to the bike and it started making the metal clanging sound a few minutes after running it. Thoughts??

2door the piston or either head doesn't have marks like they hit each other at all which is confusing why I am breaking heads.

I am about to take the needle bearing out and inspect it. How will I know if it is bad? Greg you are saying that if it is bad than the piston could travel up higher and then hit the head and cause the cracking? Wouldn't there be a mark on the head then? I am so confused.

 

[johnsoma]

Okay so I just took apart the toped to get a look at the needle bearing and wrist pin. They all look fine to me. nothing is mangled, clearances look good. I am clueless. Take a look at the pics.
https://www.dropbox.com/sh/ounaax5dwoyp1ze/AACa4nSRlJxhxBZBLHdlaD-wa

Could the knocking be a fuel/air ratio issue? Could that start cracking heads? I am doing the beginning 16/1.

Should I just buy a new engine? They are $95.

 

[rangefinder]

I would say keep digging to find the issue.
Actually I am really interested in your findings.
See, I am getting a quiet clanging sometimes.
Head is not cracking, and see noevidence to explain why it happens.
I have a few hundred miles on mine now too.

...weird.

 

[mapbike]

Okay so I just took apart the toped to get a look at the needle bearing and wrist pin. They all look fine to me. nothing is mangled, clearances look good. I am clueless. Take a look at the pics.
https://www.dropbox.com/sh/ounaax5dwoyp1ze/AACa4nSRlJxhxBZBLHdlaD-wa

Could the knocking be a fuel/air ratio issue? Could that start cracking heads? I am doing the beginning 16/1.

Should I just buy a new engine? They are $95.

All those parts you show in the pix look normal and in good condition.

I'd sure lime to know what you having going on with the knocking sound you say you have, sounds to me like something is warped hitch caused the heads to crack but without actually seeing the entire engine in front of me I can't say that is for sure the case.

I wish I could tell you what the issue is but with everything looking so good on the top end like that I just dont know what the big knocking sound could be.

best wishes....

map

 

[Greg58]

John you have a tuff one here, did the engine make that sound as soon as it started or after the head cracked? One thing you will need is a torque wrench, I have several due to my job but you can get a fairly good one for home use at harbor freight for around $25. The one below I got for $12 on sale.

 

[johnsoma]

What is the proper torque setting for the head bolts? in./lb?? I will use a friends torque wrench.

Is there a technique to this or just go in a x pattern a little on each bolt until proper torque is reached?

 

[Greg58]

I use ten foot pounds or 120 inch pounds. X pattern a small amount at a time till you reach the setting.

 

[crassius]

also, with Chinese parts I've often taken 2 parts out of a crate & found both bad - could be just bad luck, but if someone near you has a bunch of old heads lying around, you might try one before spending more money in case there is something else causing it

I recycle 15 or 20 dead engines a year, but save any old parts that are good - someone near you might do the same.