Found out why my motor died this time...

[Re-Vision]

I know that we have some good mechanics out there, but I developed this philosophy a long time ago about engines that once someone (professional or amateur) overhauls an engine they are likely to have numerous problems thereafter. Consequently I've used only new or salvaged engines since and I feel that I've saved money and frustration over the years. Anyone agree or disagree as to my making this decision years ago?    BDC

P.S. I just posted in all categories because I thought it might stimulate someone to post something.

[arthurdent510]

I agree with you, but I let my ego get the better of me at times.  That and with my last rebuild, buying a new crankshaft was cheaper then buying an entire motor.  On the positive side, I can drop and strip a vision motor apart inside a couple hours now  ;D  I'm counting it as practice for my next project, a '72 Triumph GT6.

[davexz]

I'm still wondering what went wrong.  Did the other valve look bent?  I'm wondering if the bolt that holds the cam sproket didn't come loose and then the little sprocket locating pin fell out or sheared off.  This would let the valve timing go on you and the valves could hit the piston.  Most bikes that I've worked on use a 3 bolt patten to hold the sprocket and I think they are less prone to loosen up than 1 bolt.  Also, the Yamaha manual I use has an error in a torque diagram for this cam sprocket bolt (it is right else where in the book).  In the diagram in the back it says something like 5 or 7 ft-lb torque instead of like 51 ft -lbs.  They have arrow callouts mixed up.  I hope others catch that.  This bolt they really want torqued to keep it from coming loose.

[davexz]

As far as motor rebuilds - it is like anything else people do.  Some do a good job, others don't know how to turn a wrench.  I'm not much into blanket statements though.  I have had a lot of sucess working on engines for that last 30 years. I think a person will go broke not knowing how to fix things. :)

[arthurdent510]

The heads on the other 3 valves in that head were pretty mangled... not sure if it was caused by what was left of the broken valve bouncing around inside the head or not.  Probably will never know what caused it :-(  Chalk it up to mistress number 2 trying to demand some more attention!

[Walt_M.]

Probably the reason most rebuilds fail is trying to reuse worn or otherwise damaged parts. Hence my earlier caution on checking the con rod after a valve or piston failure.
As to why that valve failed, it was 28 years old and no one really knows how much abuse it has endured in that time.

[Re-Vision]

David, are you near the point of knowing what shims you are going to need?    BDC

[arthurdent510]

Probably not...  I'm going in for some surgery on Friday, and between that, recovery time, and the holidays, it will probably be a few weeks...  Don't wait on me, if you are...

[Re-Vision]

Nah, just wanted to know how it was going and if you needed shims or any other parts from my engine to get yours' up and running. I ain't providing any organs in case your surgeon requires any extra parts for your body.    BDC

[h2olawyer]

Best wishes on your surgery!  Hope it's nothing too serious but any time it is necessary to cut into a person, it isn't trivial.  Remember your towel, your tea & most of all, Don't Panic!   ;)

H₂O

[jasonm.]

Kenny may be correct on that valve adjustment. I bought my '82(since sold). It had an original 5k miles on it. ALL the exhaust valves had closed to half of acceptable spec. Do not ignore this maintenance....every 12-15k miles after the 1st check. 1st check should be done by 8k.  The damn ethanol in the states cause hotter valves and increased wear.

[supervision]

 Sorry about your motor, failure. I had the cam timing of the rear cly slip and when it happened, the valves hit the piston.  My bike had a taping noise like a lose valve noise, only heard at idle, turned out to be the nut on the crank, that keeps the drive gear for the balance drive, as well as the gear behind that, which drives the timming chain sprocket. The noise was from the key working back and forth. I made my own key and fitted it in, but I only tightened it as good as I could and then bent the tab over.  Back together, the engine sounded LIKE NEW. I was riding, it started making some noise, I thought I could limp it home, didn't make it, stopped at low engine speed, and then I took it apart, the key I had made was sheered and the gear had moved about 5 teeth, So I re timed with the old key and I now only runs on the front cyl.  Because my engine has 59,750 miles on it, and because, I'm a much better RIDER, than engine builder, I am not EVEN going to take it apart!

[arthurdent510]

More damage I found last weekend...  I had already replaced the 2 cams on the front cylinder where the valve dropped.  This was on the rear cylinder, both intake and exhaust cams had hairline cracks right at the pin.  So more cams on order  :(  One of my timing chains was slightly stretched as well, so I replaced both of them.  It's slowly coming back together... at least the motor is more or less back in one piece again!

[fret not]

Aside from the crack, the surface of the journal looks scuffed.  Once something has come apart (wear) in tiny pieces all the oil galleys need a thorough purging and all interior surfaces need to be thoroughly washed and blown off with compressed air.  ALL the surfaces, bearings too. :police:

In regard to an early statement re factory vs rebuilt, a lot of the dependability depends on how clean things are when they go together.   The mind set of "Whatcha cain't see cain't hurtcha" exists in all too many shops and home workshops, while the factories have clean rooms and are meticulous in how they put stuff together.  They do it all day long and become very good at that process, while we tend to struggle as we tend to the occasional deep involvement with our trusty rides, seldom if ever achieving a fluent relationship with all the bits and pieces.  If you want a professional quality result you have to have a professional attitude as you go through all the steps until she's a runnin' again.  There is no room for being lazy in this regard. ;)

[VFan]

One of my timing chains was slightly stretched as well, so I replaced both of them.

How do you tell, measuring the circumference or just comparing the two? It's a beefy chain so I'm surprised that they actually stretch. Is this a common wear item?

Separately, when I look at the pics (thanks for posting them) the question comes to mind if there is any value in tearing apart an engine (perhaps once every 10 years or so) and dip it to get rid of all the deposits. My heads have quite a bit of build-up and I've wondered about that.

Thanks in advance,
Kent

[fret not]

Regular oil changes are key for keeping sludge from building up.  Also, making sure your motor is thoroughly heated up for a good while, especially in cooler weather.  If it doesn't get totally hot you can get internal condensation building up.  Short rides are likely to contribute to this.  I had this problem with a Norton in the 70s.  It seldom got run hard enough to cook off the internal moisture, so when checking valve clearance the covers would have a white emulsion in them, and when I poked my finger into it water beads would come out.  Just oil and water, but that is a serious ingredient for creating sludge.