Engine re-assembly

[georgesgiralt]

Hello Guys,
I've a question that puzzle me since a long time.
Suppose I remove the heads of my engine. Then when I assemble them, I put the engine at top dead centre, then adjust one side for the correct gap at the valves, turn the engine wheel one full turn and adjust the other side.
Question : is it good or should I choose more carefully the first side I adjust ? And if not correctly done, what are the drawback and the risks ? And how could I tell when the engine is closed if it has been assembled rightly ?
Thanks in advance to help me before the champagne clouds my mind and gives me more headache than it already has ;-)
In the meantime enjoy your day !

[Barry]

If you put the engine at TDC.  When inserting the pushrods it should be possible to tell which side is "off cam" by comparing the length of pushrod protrusion.  The side with least pushrod protrusion will the first side to assemble and adjust the valves. You can then rotate  1 turn to assemble and set the other side.

[georgesgiralt]

Hello Barry,
Do you think it can be assembled backwards ? I.E. with the wrong side set with valve clearance instead of being on pressure ?
I've an engine performing strange and wonder if it's not a bad assembly (it has been serviced recently).

[Barry]

Hello Georges,

I don't think you can do it wrong and still have the engine run.

[georgesgiralt]

OK, so I'll check elsewhere...

[Luca]

Georges, were the heads re-torqued after running the engine a bit, and if so, were the valves checked after that?

[georgesgiralt]

Yes, the engine had run around 3k  km since and the valve lash has been set 3 times (now a bit on the noisy side, BTW).
The bike runs fine when hot and very very rough cold een with the choke on full.
Next week end I will change the rubber boot between the head and the carbs. One seems to be in bad shape.

[Luca]

Well if you suspect poor engine assembly you could do a compression test while you are replacing the lower carb boot to help support or rule out your suspicions.  You'd want to do this after making sure the valves are set.

If the hard starting is not a carburetor issue, the next suspects would be valves or ignition.  I know you've checked the valves, but if you haven't retorqued the head nuts since reassembly there could be interplay between that and the valve lash.  I would expect it to loosen the valves, since the loose heads would be further spaced from the engine case and pushrods.  That extra slop, if it is there, might explain the valve clatter.  Since the heads should be installed "off cam"  (on the compression stroke) you might also want to re-torque them that way.

[georgesgiralt]

OK,
I'll take all your advices ! In fact the engine had new piston rings installed around 8 month ago, and had leaks at the cylinder bases and on one push rod tube. So about 3 month ago I removed the heads and put Permabond on the base, new O-rings (and found one swelled O ring), new head gaskets and new push rod grommets.
Since then, I had difficulties syncing the carbs. If the setting is perfect at cold idle, it becomes erratic when the engine is hot. If I adjust for the hot engine, then the cold engine is bad.
I've questioned my depressiometers, so I put into use the U device I planned to use since a very long time but without any luck.  Transition from idle is also bad either when cold or when hot. Engine push good (as far as I dare go in order to keep my license and money...)
I've, of course, re-torqued the heads, adjusted the valve lash, checked the carbs for deposits, water or grunge, checked the diaphragms and put new spark plugs just in case.
During one adjustment I saw that the grommets on the heads are somewhat cracked. So I ordered new ones and I plan to install them when the champagne bubbles have evaporated ....

[Luca]

Transition from idle is also bad either when cold or when hot.

That makes it sound like an imbalance issue, either compression or carburetion.  If it isn't an air leak or a cylinder with poorly set rings, the only other thing I can think of that you haven't mentioned is to make sure the fuel levels in your carb bowls are relatively equal.