I had some trouble getting my new 686 back together if you read my other post. I finally got everything working and it ran like a champ. I broke it in yesterday and went to the sand drags today. After my first pass for dial in, I noticed some oil was leaking around the front of the lower cylinder gasket. I found that the little allen bolt on the front left side of the cylinder was loose so I tightened it and headed back out for my first round of eliminations. I had expected to run faster, but I ran a bit slower. When I got back to my pits I found that oil had sprayed out the front of the engine at the lower cylinder gasket area. When I wiped the oil off I noticed a big crack in the lower front portion of the cylinder. Check out my pics page to see it.

Now for the questions.

1) The engine was put together by the Yammie dealer (twice). Should they be held responsible and made to fix it for free?

2) Does it look weldable or should I go for a new cylinder?

3) I heard that head and valve cover should be a matched set. What about head and cylinder?

4) If I get a new cylinder should I have the top surfaced to make it perfectly flat and smoothe or does it come that way already.

5) Any tips to keep this from happening again, other than telling the mechanic to remember to torque the bolts?


Thanks for all your help,

RR1

 

The cyl. is not matched to the head or the case.
I don't know how they come but the surface should be checked.

 

I would think that they would cover it considering they damaged it. I would take it back and see what they say.

 

Anyone have any idea what may have caused this? Anything besides not torquing the cylinder bolts down? Thanks,

RR1

 

kinda sounds to me like it was over tightened. They probably didn't use a torque wrench on it.

 

I don't know if not having that one bolt torqued down would break it. And I doubt you could break it by over torquing it with that little bolt, especially being threaded into aluminum. I would say they dropped it, but it doesn't look like it has any damage marks on it from a fall.

Personally I would try welding it first (but I'm cheap too). You would deffinately eed to check everything out after it was done though, ESPECIALLY make sure the bore is still round. If it does deform it you can always have it resleeved. If it is cracked all the way to the base gasket it might be hard to get the bottom of the cylinder flat after welding it.

A cylinder looks to be about $318, then add about $40 for a bore job to fit your piston.
Somebody could weld it for approx. $50. You need to find somebody that is good though. I am no welder, but it seems like a deep crack in aluminum would be hard to do...maybe I'm wrong though.


good luck

 

My guess would be either:

The larger cylider bolts are loose.

The cylinder was cocked or hung up on a dowel pin when they assembled it and pulled it down with that bolt and cracked it.