[lil-legzgtr]

im helping out a mate who is doing some engine work on a suzuki freewind (650 single) and he has taken the cam out without finding TDC and marking the cam, i cant figure out how to find it again? where shouls the piston be at TDC and where should the valves be in relation to this? any help would be greatly recieved.

 

[southernman]

There are almost always marks (little dots or triangles) that are stamped into the cam and crank gears that indicate timing alignment marks. The ones I've seen typically are aligned to point at one another. My hillbilly way (sorry fellow Kentuckians) of finding TDC for the piston was to remove the sparkplug and insert a screwdriver. Turn the engine over by hand and watch the depth of the screwdriver moving up and down in the head. Remember though, the crank turns two times as fast as the the cam(s) so there are two possible choices for TDC in the cam-to-crank relationship. One will work while the other will have the spark plug firing at the top of the exhaust stroke and the engine will not start. Look closely at the gears, there has got to be some indicator mark.

 

[lil-legzgtr]

cheers for the info m8. being a single there is a mark on the cam to show when all valves are closed, what i really need to know is where should the valves be when the piston is at the very top of its stroke, i thought they they should be all closed at the top of the stroke but when we tried this the piston touched the valves on the exhaust side? we tried going one tooth back and one tooth forward but it still touched and without a manual were stumped?

 

[southernman]

Most of today's modern engines use a concept called "valve overlap", the period when both valves are open near TDC. So on your engine your assumption of valves closed at TDC may not be correct.

Are you looking only at the cam gear or do you have the crank gear exposed also? The crank gear will have reference marks as well. Some older Hondas had a mark on the crank gear that had to align with a mark on the engine case. Once the crank is set, then move to the cam gear indicator. On new Honda CRF's, the dot on the cam gear has to be in parallel with the head gasket surface so in this case there's no reference point on the case. You almost have to be overlooking something. Think about an engine in a production environment. If the setup were left in the hands of the assembly worker and the process was this mysterious the manufacturers would never meet production.

Good luck,

 

[phlat65]

another acurate method to finding true TDC is the piston blocking method.
fashion some find of stopping bolt that can thread into the spark plug hole and stop the piston from reaching the top of it's stroke (20 deg of crank rotation is good). slowly rotate the crank until the piston contacts the stop and can no longer move up. make a mark on the flywheel in reference to something on the case. rotate the engine the other way and do the same. the difference between the 2 marks is true TDC.

 

[lil-legzgtr]

cheers guys, i got it runnin and it sounds ok but the header is getting very hot very fast? i think it may be a tooth out because he says he dosent remember ir getting that hot that fast before?

 

[southernman]

Assuming you didn't do anything to the carb and the motor's not running excessively rich, then the timing needs to be advanced. Drastically retarded timing will cause the headers to glow since you're basically burning gasoline in the header instead of the cylinder.