Topic: Engine Rebuild - How to Determine #1 Cylinder is on Compression Stroke?

[AintNoEasyWay]

Hey guys, trying to close up this K7 engine I've got. I'm having trouble figuring out whether I've set my cam to be on #1 or #4 compression stroke at TDC. Both my rocker arms on #1 and on #4 seems to be loose, as I show in this video:

Here's what my cam looks like, notch on right hand side faces up while matched to 1-4 T mark, lobes on #4 face down while lobes on #1 face up and slightly out, like a "V".

How do I determine if my cam is set up correctly? Couldn't it be on #4 compression stroke instead? Everything I've read just assumes the cam is already set up and skips to valve adjustment. Thanks.

[jonda500]

You have #4 on compression stroke (lobes down = rocker arms not holding valves open = compression stroke)
rotate 180 degrees so #1 has its lobes down

[AintNoEasyWay]

You have #4 on compression stroke (lobes down = rocker arms not holding valves open = compression stroke)
rotate 180 degrees so #1 has its lobes down

So the notch on the end of the cam should actually face down when I set it up? I'm confused because all the pictures/write ups have it facing up with the lines matching the cam tower bearings/caps.

[jonda500]

I have only done 400/500/550 cams but I don't think it matters either way(notch up or notch down) as the points fire every stroke on these? Wait for a 750 expert to chime in if you're worried

[calj737]

500/550 cams notch to 3:00/9:00. But, the position of the cam lobes on 1/4 will tell you which is in compression. don't overthink what is happening with your rockers currently, especially if you've adjusted them improperly.

You can also determine which cylinder is at TDC by removing the spark plug, and using a wooden stick to measure the cylinder depth between 1/4 to confirm where the piston is.

[AintNoEasyWay]

500/550 cams notch to 3:00/9:00. But, the position of the cam lobes on 1/4 will tell you which is in compression. don't overthink what is happening with your rockers currently, especially if you've adjusted them improperly.

You can also determine which cylinder is at TDC by removing the spark plug, and using a wooden stick to measure the cylinder depth between 1/4 to confirm where the piston is.

Thanks, calj. So I'm currently 180 out? Not sure if you're agreeing with jonda. Should lobes on #1 face down instead of up like mine do in the photo? My guess would be that if the lobes face up, then the valves are pushing down toward the cylinder, is this correct?

[calj737]

My answer is: time for you to learn how to determine that. I gave you a technique that's super easy, sure fire, and then, you can understand the cam. I'm not trying to sound prickish, but this is something to learn not be told.

It will take you 5' for a lifetime of knowledge 

[AintNoEasyWay]

My answer is: time for you to learn how to determine that. I gave you a technique that's super easy, sure fire, and then, you can understand the cam. I'm not trying to sound prickish, but this is something to learn not be told.

It will take you 5' for a lifetime of knowledge 

Cool, thank you, calj.

[goldarrow]

Just for the record, calj is mentioning about 500/550 bike, but you're working on 750.  You'll be chasing your tail end if you do either 3 or 9 o'clock notch positions that he mentioned ealier.

[jonda500]

You'll be chasing your tail end if you do either 3 or 9 o'clock notch positions that he mentioned ealier.

would just have to simply swap over the blue & yellow wires if you did that - or assemble the centrifugal advance with the cam turned 180 degrees 

Edit:   stick with 12 or 6 o'clock - I didn't mean to confuse/derail the thread

[goldarrow]

You'll be chasing your tail end if you do either 3 or 9 o'clock notch positions that he mentioned ealier.

would just have to simply swap over the blue & yellow wires if you did that - or assemble the centrifugal advance with the cam turned 180 degrees

Oh oh...don't mention this....180 degrees out is just like an oil thread....you've been warned....

[flatlander]

when you are at TDC, valves can be closed or opening/closing depending on crankshaft position. compression stroke is when you're at TDC and valves are closed.

my pictures are on a 550 at TDC but the same principle applies to 750.

no.4 is on compression stroke:


no.4 is on intake stroke:


if you look over to no.1 you see the same happening there, in reverse order.

[Bailgang]

You have #4 on compression stroke (lobes down = rocker arms not holding valves open = compression stroke)
rotate 180 degrees so #1 has its lobes down

So the notch on the end of the cam should actually face down when I set it up? I'm confused because all the pictures/write ups have it facing up with the lines matching the cam tower bearings/caps.

You are WAY over thinking this and everyone talking about a 500/550 doesn't help. In your video so long as 1-4 cyls were at TDC then it looked like you had the cam set correctly that is the notch facing up at 12 o'clock with the lines matching the cam bearing cap. It really doesn't matter whether that notch is at 12 or 6 when 1-4 are at TDC, what DOES matter is that the lines match the cam bearing cap end but just to avoid confusion then stick to having that notch at 12 o'clock.

This whole 180 degree scare has to do with cam timing not with the cams actual position and that screw up can only happen if you had the 2-3 cyls at TDC when setting the cam in place rather than 1-4 at TDC.