QuestionQUESTION: Hi,
I'm working on a 1973 Honda CB350G. I have rebuilt the top end, and cant seem to fire it up. Fuel, compression, and timing are right on. Someone told me my camshaft may be 180 degrees out. I have stared at the parts for a while now and cant seem to figure it out. Need your expert advice. Is the right plug firing when the left cylinder is top dead? How is that fixed? Anyways, thanks a ton for your advice on the matter.
Nathan from San Diego
ANSWER: Hi Nathan,
I think the easiest way to verify things are correct
may be to watch your intake valve opening and then
bring the left cylinder up on it's compression stroke.
This will be near "TDC" for the piston. The "F" mark on the
rotor should be aligned for checking the ignition timing.
Now check your left set of points are just breaking open.
If they are not then something is out a whack.
Check the points cam and advance unit just in case it
is assembled wrong or the pin it locates on is stripped.
The left points should just break open when the
left cylinder is at "F" or (maybe "LF") on it's compression stroke.
Good animation: http://oldmanhonda.com/MC/Rtiming.html
Also make sure the left points are connected to the
left side coil.
If the points cam looks okay then you may have the camshaft
timed incorrectly. If so, maybe you can loosen the
cam chain and turn the engine 180 degrees if the lower
sprocket will clear the chain.
Watch out that pistons are half way down in the bores
if you move things around. Don't want any bent valves.
So, the point is it should be easy to check by watching
your valve openings and the points opening.
Carbs and jets should be cleaned too.
If you get the spark going then you can always
spray some carb cleaner or wd40 in the carb mouth
to see if it will fire on it.
I hope this helps a bit.
Wayne S.
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---------- FOLLOW-UP ----------
QUESTION: Hi Wayne,
Thanks again for your previous answer, it got me going in the right direction. I found out that my left point starts to open at the beginning of my intake stroke. Does this mean my camshaft is 180 degrees out? Thought I'd ask before trying this operation again. Also, my advance unit, locate pin are in good shape and left points are connected to left coil.
Cheers, nathan.
ANSWER: Hi Nathan,
Yes, it sounds like your camshaft is out
about a half turn. That means the
crank-shaft has to make one more turn
(360 degrees) to be on the compression stroke
where the points should just be opening,
with the "LF" timing mark aligned.
(Also double check that your small cam on the ignition
advance unit is not inserted 180 degrees out)
When the "LT" mark is aligned on
the rotor there is an "L" mark and
line on the camshaft sprocket that
should be lined up at the top of the motor.
The sprockets "L" will be straight up
and the line will be lined up
with the cylinder head surface horizontally.
http://farm1.static.flickr.com/215/469120224_15b1d10ccf_b.jpg
The "LT" mark means the piston is
at the top and the left side cam lobes
should not be opening any valves
at that point.
It is a bit confusing but just
align the marks and make sure
the left points will break open when the
engine is on the compression stroke
with both left valves closed.
Then it should run!
Be careful not to bend any valves
when moving things around. Just
be gentle and it should be okay.
More luck!
Wayne S.
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---------- FOLLOW-UP ----------
QUESTION: Hey Wayne,
She fired up, first kick and strong. It was the small cam behind the breaker points!! I had it on 180 degrees out, crazy, cause there isn't anything about it in the manuals. Thanks!
It does have a tapping sound from the top end. I think on the right side. Oil is at top dash, maybe a little over. I should let a little out of the drain plug. Cam chain has good tension, plus its a new chain. The timing is perfect. She idles perfect with no backfires or smoke.
So, what do you think about that tapping noise on the top end?
Thanks a ton Wayne!
AnswerHi Nathan,
Glad to hear yuu got it running.
The top end commonly makes a little
noise but pull off the valve adjust
cover and make sure the oil is spraying
around the top end okay.
If it looks fairly oily in the
top then you can try rechecking the
valve clearance again. The exhaust rocker
might just be slightly loose.
They will make some noise at the standard settings.
This is usually safer anyway.
Even .002" can make the difference between quiet
and noisy on these.
It might be better to run a bit loose until
it all breaks in a bit.
Later on you can tighten the exhaust
settings a little.
Always keep at least .002" clearance.
This is just perceptable with your fingers.
Some noise can be attributed to new piston rings.
It takes time for them to wear into the cylinder.
Air cooled engines do not have the sound deadening
characteristics of liquid cooled engines.
The cooling fins transmit noise everywhere.
If it is severe noise it could be a worn cam or rocker arm.
If it is getting oil to the top end I suspect it
is normal valve noise. I have heard many noisy ones.
Just keep an ear out for any big change in the noise
and enjoy riding!
Have fun, good work!
Wayne S.
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