Valkyrie backfiring - FIXED!!!

[indybobm]

Q: Will having the crank set to Cyl#1 guarantee it to be in proper position to reinstall the belts?

or, Is it possible that the crank could be in either the compression or exhaust stroke at that setting?

After I removed the heads and sent them off to the machinist, I did turn the crank to inspect each piston closely.  The thought came to mind that while the timing marks may line up properly the crank may not have been in the proper stroke cycle for Cyl#1 when I realigned and reinstalled everything.  

Thoughts?

Q: Will having the crank set to Cyl#1 guarantee it to be in proper position to reinstall the belts?
A. If the camshaft pulleys are aligned correctly.

Q:or, Is it possible that the crank could be in either the compression or exhaust stroke at that setting?
A. When the crankshaft pulley is at T1.2, cylinder 1 is on the compression stroke and cylinder 2 is on the exhaust stroke. What  stroke a cylinder is on is dependent on the design of the camshaft .

Keep in mind, in my earlier response I said that I DO NOT think this has anything to do with the problem. I was just responding to someone else's comment about rotating the camshaft.

[Jersey]

Q: Will having the crank set to Cyl#1 guarantee it to be in proper position to reinstall the belts?

or, Is it possible that the crank could be in either the compression or exhaust stroke at that setting?

After I removed the heads and sent them off to the machinist, I did turn the crank to inspect each piston closely.  The thought came to mind that while the timing marks may line up properly the crank may not have been in the proper stroke cycle for Cyl#1 when I realigned and reinstalled everything.  

Thoughts?

Q: Will having the crank set to Cyl#1 guarantee it to be in proper position to reinstall the belts?
A. If the camshaft pulleys are aligned correctly.

Q:or, Is it possible that the crank could be in either the compression or exhaust stroke at that setting?
A. When the crankshaft pulley is at T1.2, cylinder 1 is on the compression stroke and cylinder 2 is on the exhaust stroke. What  stroke a cylinder is on is dependent on the design of the camshaft .

Keep in mind, in my earlier response I said that I DO NOT think this has anything to do with the problem. I was just responding to someone else's comment about rotating the camshaft.

Appreciate the follow-up and understand this was a theory discussion.  I didn't think it had anything to do either, but am always interested in other's views.

I had a feeling that the marks were for the TDC for the identified cylinders, but I couldn't locate a hard source to prove it.  Just made sense from a design aspect and what I've experience with engines before.

Appreciate the discussion!

[Cracker Jack]

After I removed the heads and sent them off to the machinist, I did turn the crank to inspect each piston closely.  The thought came to mind that while the timing marks may line up properly the crank may not have been in the proper stroke cycle for Cyl#1 when I realigned and reinstalled everything. 

The cams (valve timing) alone determines which stroke cycle the engine is on. The crankshaft and pistons just go up and down and round and round and respond to the stroke position as governed by the cams. Your thought is not valid.

[oldsmokey]

Is there any follow up with this issue or is still in the shop?

[Jersey]

Is there any follow up with this issue or is still in the shop?

Still in the shop. Thanks for asking.  I'm on travel right now, so expect it to be ready when I get back in a few weeks.

[Jersey]

First, I want to thank all of those who provided suggestions/feedback! 

All is running very well now.  Here's what happened:

1. Changed timing belts (precautionary maintenance at 60k)
2. Timing was done correctly
3. valves were burnt (3) and compression was low so had the heads/valves redone.  Compression is great and leak-down tests are excellent.
4. Coincidence: Pickup timing sensors needed replacing.  While they appeared to work 90% of the time, there seem to be an intermittent issue... always difficult to identify.
5. Coincidence: Carbs needed cleaning.  Apparently, during the timing belt & head work some dirt in the carbs (cyls 1, 2, &5) became loose and clogged them up. 

So.  Now the bike is running what feels like new.  Feels like I have maybe 20% more pull compared to before I started all this.  The exhaust sounds SO much better!  Clear & crisp. 

I'm relieved that at least I still know how to time an engine!  That was my original concern that the ol' guy forgot the basics.  It's interesting thought that I mis-diagnosed and completely overlooked dirt in the carbs.  I can only figure that my assumption was these would continue to be fine since the engine was running fine beforehand.  The intermittent pickup sensor is just a PIA that happens from time to time.

Again, Thanks ALL!  Really appreciate the support and discussion.

Cheers and Ride Safe!

[The emperor has no clothes]

Glad you got her worked out. 

[oldsmokey]

Excellent, hate those multiple issues that come from different directions.

[Bagger John - #3785]

How did the valves get burnt?

[Jersey]

How did the valves get burnt?

I couldn't say.  The machinist speculated that the desmogging changed the cooling effect those ports had on the cylinders and it let to an increase in heat and pressure.  Over time the valves got burnt.

[Harryc]

I couldn't say.  The machinist speculated that the desmogging changed the cooling effect those ports had on the cylinders and it let to an increase in heat and pressure.  Over time the valves got burnt.

Well, guys have been de-smogging these for years and I never heard of it burning valves. You'd think it would have occurred frequently in the past if it was a problem. There's that, and the fact that all of those capped vacuum ports on the engine side go to the crankcase.  Cylinder cooling would come from the radiator/water pump/coolant. More likely was a lean condition causing excessive heat over time.

[da prez]

  When an engine is rebuilt , the crank is turned several times setting the pistons. The crank is set on a tdc (or timing mark) and then the cam timing is added. If done by the book , all should work in harmony. Turning the crank with the heads off (no timing belts) will do no harm.

                             da prez

[Dirty Dave]

Enjoyed following the thread.

I love a good mystery story.