Crank Inspection

[dave M]

I have a 1200xl pv fast :D !! Until rescently

I had a oil line fall off the carberator and one of the pistons overheated. It still ran at an idle. The compression showed me which piston was toast. Pulling the head showed me what the piston and cylinder were toast. I pulled the cylinder and piston. Now the $500++ question is -- is the crank bad...
I have recieved several opinions and the crank is still in the boat.

The Rod seems to have no slop and moves very freely and there is oil in the bottom of the crank....help!!!!

[Technical Support]

Re: Crank Inspection

Without a doubt.

Here's a quick lesson on engine design. Two strokes get the air/fuel/oil mix from the intake, which is drawn into the case and swirls around - lubricating the bearings and rods. It then gets pushed/sucked up into the cylinders, burned and ejected.

If you have a lack of oil situation, the first thing lubed is the first thing damaged - the crank. Just because it hasn't fallen apart doesn't mean it's not damaged! A tire can be flat without it being shreded can't it?
As I said on the phone you can repair it anyway you like. But it's not a question of 'if' the crank will fail, should you choose to just sleeve a cylinder and throw a piston in it. It's a question of 'when' and 'how many hundreds MORE' will you spend to fix it then.

This question is asked many, many times, and no one believes it the first time around.

[Phil STX15F]

Re: Crank Inspection

If you had a piston "overheat" then your crank is going to have very small aluminum particals all over your bearings in that cylinder. How's your luck? Do ya feel lucky? You can put it all back together with that crank to save money but it mite cost you more in the long run. Like when a bearing goes bad and takes out your cases and cylinder.

[d.ginther]

Re: Crank Inspection

I have a 1200xl pv fast :D !! Until rescently

I had a oil line fall off the carberator and one of the pistons overheated. It still ran at an idle. The compression showed me which piston was toast. Pulling the head showed me what the piston and cylinder were toast. I pulled the cylinder and piston. Now the $500++ question is -- is the crank bad...
I have recieved several opinions and the crank is still in the boat.

The Rod seems to have no slop and moves very freely and there is oil in the bottom of the crank....help!!!!

Certainly the "right" way to do it is to replace the whole motor.
I had something similar happen with a ZXI900 - oil injection to one of the carbs failed.

I ended up doing a "cylinder exchange" from SBT.
I notice no problems on inspection with my crank - no signs of wear or excessive play.

My cylinder was scraped, would need to be bored, but I don't think that there was much metal - if any deposited in the crank. Have a look:
http://lakebox.dnsalias.com/photos/9...d/DSC04611.JPG


My theory:
The majority of the heating and friction occur in the cylinder. When you don't get enough oil, that barrier that protects from wear is gone.

The crank and the rods have roller bearings in most cases and aren't as subject to tremendous heat (combustion).

I think the crank might be fine - but you need to inspect it for play and wear... How many hours are on it?

Like posted - the only way to be sure is to replace it.. I'll post if mine fails, right now it's running great.

Oh yea - another plus - SBT will warranty the whole motor, but not just the top end if that's what you go with..

[dave M]

Re: Crank Inspection

OK ---I bought a new SBT crank... got a calendar too:emoticonw


Question on breakin? is there special oil or breakin procedure?

Also bought the oil block off kit ... Is there any modifications that need to be done to the carbs now that I'll be running mixed oil?

[Technical Support]

Re: Crank Inspection

Only new top-ends require break-in. No carb tuning is needed.

[dave M]

Re: Crank Inspection

Oh- well I did replace one cylinder and piston. What is the procedure for two old ones and one new one?:emoticons

[Technical Support]

Re: Crank Inspection

Read the break-in article.

[dave M]

Re: Crank Inspection

where?

[Technical Support]

Re: Crank Inspection

The Tech Articles section, page 2.

[dave M]

Re: Crank Inspection

Thanks,


How criticle is the PTO torque of 54 ft lbs ? I cranked on it doesn't is spin such that the PTO tightens?

[Technical Support]

Re: Crank Inspection

Get it as tight as you can - it self tightens the first time you put it in the water.