[milesoffun]

I'm trying to put this one back in the dirt!

Bought it with the crank stuck. Got it free - but had to take off the head/cylinder to get it free. I did not have to split the case. I've put it back together and she spins good and generates what looks like good spark. But does not even try to start. I can spray "go juice" in the cylinder, put the plug in, and still not even a single hint of trying to start.

I put new rings (original size) when I had it apart. Using a low cost (HFreight) compression tester I get about 80 PSI which is probably low, but I would think it still try to run. I put new points and spark plug in as well. I have worked on the timing many times and I think it's right, but I have to wonder - I have the shop manuals and I think I'm following them but I can't help but think timing is my issue since I get nothing after spraying the go juice.

When setting the timing, at the instant the points open, both intake and exhaust valves are supposed to closed, right? I'm having real trouble getting the timing marks to even get close to lining up when setting the points. It seems to be far away (1/4 turn) from the mark with I reach the F mark on the flywheel?

Any suggestions to try appreciated! I have read most of the similar post's here that i can find but so far, no luck.

Thanks!

 

[johnnyvee]

I'm trying to put this one back in the dirt!
had to take off the head/cylinder to get it free. It seems to be far away (1/4 turn) from the mark with I reach the F mark on the flywheel?
Thanks!

What you said seems to suggest that when the head was re-assembled, the relationship of the cam to the crankshaft, via the chain, was set incorrectly.

I assume that the stator is keyed to the crank so it can only go on in one way?

I don't have that engine myself, but the reference material I do have says,

"Insert camshaft with with lobes of cam toward top to clear notches in head, through cam drive chain and into head. Turn camshaft 180 degrees so that bolt holes are aligned vertically with cylinder bore. Place crankshaft in TDC position, "T" mark on rotore will be aligned with index mark, and install cam drive sprocket in chain so that "O" mark is in top center of cylinder head. Install bolts. Cam timing is correct if "O" mark on cam sprocket is aligned with chisel mark on cylinder head and "T" mark on alternator rotor is aligned with index mark on stator "

I'd recheck the crank to cam relationship. Good luck!

 

[milesoffun]

Thanks - that had been bugging me for sure - I'll give it a try over the next couple of days. I'll need to get it back apart and read your instructions a few more times and see what happens!

 

[johnnyvee]

Note that having the valve timing off with respect to the crankshaft will also likely have a negative effect on compression, less of the stroke will be with the valves in their closed position.

One must be very careful with setting this relationship. If it's far enough off, in most overhead valve engines, the piston can hit the valves, ... always a BAD thing.

 

[milesoffun]

Understood!

 

[milesoffun]

Understood!

Removed the camshaft - followed the instructions on getting it back in as described, lined up everything just right I thought. Put it in lobes up and then turned it down 180 to get it to fit in the opposing hole. Got it lined up with the sprocket - and T mark - looked great. Followed the manual on timing and points and I'm back where I started! I'm a good quarter of a turn off and I cannot get it close advancing or retarding the timing. I thought I would post the pics after the attempts to see if I can get some other ideas. I've worked with points bikes in the past but this one has gotten the best of me so far! I know I've something wrong but I've got no idea right now what it is!

 

[johnnyvee]

Verifying that the piston is at TDC when the "T" on the stator aligns with the index mark will rule out any chance that the stator is in the incorrect position on the crankshaft. This fit is generally keyed and should go on in only one position. I have resorted to sticking a dowel or something like an engine pushrod (long enough to not be capable of being lost inside) down the spark hole as I rotate the engine over, as a reality check. With the crank at TDC position, both valves should be closed and should have the specified .002" clearance accessed through the inspection ports.

Did you take a picture of the camshaft sprocket as it was being assembled with crank at TDC? That will show the "0" that needs to be aligned to the mark on the head. This is before the breaker points housing goes on. First you get the valves to crank set correctly, then you can get the ignition timing to cam correct. I'm not sure what "chisel mark" the "0" is supposed to align with, but both valve cams should be at or very close to their minimum diameters at this point. It's not impossible for the manual text to be incorrect, so getting the mechanical system right should override the "recipe" in the text. If the camshaft is set correctly and the valves are behaving correctly, (look at some basic descriptions and pictures of 4 stroke engines if you have any vagueness on what the correct behavior is) then it's likely the breaker points to camshaft that was assembled wrong. Looks like about 120 degrees advanced to me, based on your images. I don't have any idea of how the breaker cam is indexed to the camshaft, so a picture of that might give a clue.

The points should be opening and the plug sparking with "F" at index mark when static timing with a test light or VOM, and also at idle speed if using a timing light.

Back in the day, I'd make quick pencil sketches as I disassembled, these days it's digital pictures of each step of the process. When you have an engine that isn't running when you get it, putting it back the way it was is no guarantee of success, but it doesn't hurt to have that info either.

Good luck!

 

[milesoffun]

Thanks - still looking at it. The "O" matches up with the little chisel mark so I'll keep looking. The "breaker cam" is indexed with a tiny pin placed in the cam so there is only one way for it to go on, if that makes sense to you. I'll get some more time this week to look at it and try a few more of your suggestions. I' don't believe my carb is getting gas in the cylinder, but I keep thinking the "go juice" would get a spark.

 

[johnnyvee]

Is the breaker cam separable from it's shaft?

 

[milesoffun]

Since I have it apart - I'm including the pics! Thanks for taking a look!

 

[Rizingson]

I first thought maybe the camshaft index pin was missing, but see it's in place. Have you pulled the flywheel/rotor to see if the key is intact and indexed properly. May have spun when engine seized.

 

[milesoffun]

I have not. Although the crank was stuck, the piston was free. It really seemed like maybe some rust got to the crank - or just time. Lubed with some trans fluid and acetone and let it set for a couple of days and was able to get it moving. But I'm running out of things to try...

 

[johnnyvee]

You did verify that the piston was at TDC when the rotor "T" lines up with the index mark? If the rotor is lying to you, that's confusing. The pictures you posted all seem consistent with correct assembly at the camshaft, but the crank, or at least the stator looks off by 100 degrees.

Next after that is to verify that the as the piston approaches TDC at the end of the exhaust stroke, the exhaust valve is closing and very shortly after that, the intake valve opens, and similarly after rotating 360 degrees and ending the compression stroke, at TDC both valves are closed. If this is the case, then valve timing is correct. Have you verified that both valves are opening and closing? Is it possible that you've assembled 360degrees of crank (180 degrees of camshaft) out of sync?

Here's a GIF depicting the 4 stroke cycle:

( Edit - maybe animated GIFs aren't supported, so here's a link: https://upload.wikimedia.org/wikipedia/commons/d/d7/4-Stroke-Engine-with-airflows.gif)

If that all checks out, and you have compression, modest in your case, and you have spark, as you said previously, the engine should fire on starting fluid, even if the carburetor is non functioning. If not, spark may not be occuring with the plug installed, even though it sparks when removed. Is this bike a battery powered ignition, or does it have a magneto?

 

[hogcowboy]

You did verify that the piston was at TDC when the rotor "T" lines up with the index mark? If the rotor is lying to you, that's confusing. The pictures you posted all seem consistent with correct assembly at the camshaft, but the crank, or at least the stator looks off by 100 degrees.

Next after that is to verify that the as the piston approaches TDC at the end of the exhaust stroke, the exhaust valve is closing and very shortly after that, the intake valve opens, and similarly after rotating 360 degrees and ending the compression stroke, at TDC both valves are closed. If this is the case, then valve timing is correct. Have you verified that both valves are opening and closing? Is it possible that you've assembled 360degrees of crank (180 degrees of camshaft) out of sync?

Here's a GIF depicting the 4 stroke cycle:
View attachment 60038
( Edit - maybe animated GIFs aren't supported, so here's a link: https://upload.wikimedia.org/wikipedia/commons/d/d7/4-Stroke-Engine-with-airflows.gif)

If that all checks out, and you have compression, modest in your case, and you have spark, as you said previously, the engine should fire on starting fluid, even if the carburetor is non functioning. If not, spark may not be occuring with the plug installed, even though it sparks when removed. Is this bike a battery powered ignition, or does it have a magneto?

Another work around to this very limiting function of this new format is to do a Reply. The animation will work in that mode. I've requested this be fixed or allowed by the administration but so far, this is the next best thing. Sorry but this is another that isn't the fault of the moderators folks. It just is now.

 

[milesoffun]

Thanks guys - it's a bit cold down south but will get back at it when we get back to normal. I'm going to start again and work my way down the thread!

 

[Unkle Krusty]

Good you are getting help with figuring this out. With new rings I think you should be getting around 140 pounds of pressure. Under 90 is about as low as we can go. So I am also wondering where the pressure is going. Valve seats are the other suspect. Follow the piston up and down, and the valves opening and closing, to get TDC. Then check the timing marks. TDC on the crank should line up with a marker on the casing. Same with firing a bit before TDC.

Bon chance. Good that you checked, and have spark. Sometimes you can see the spark, and the valves. Kind of like a timing light.

UK

 

[milesoffun]

Warned a bit here - here is the latest!

To catch up a bit here:

This bike has a battery powered ignition. I have a fresh battery that I keep charged. Why might it not spark when plug is installed?

As far as compression, I lapped the valves before reinstalling them and they looked to be in decent shape. I just now checked compression again and now she is very close to 125psi. Not sure why I had the low reading before but its’ better now. I just tried to check it again and I hit 125 and then it blew my homemade adapter apart. No more checking for now but I think we can maybe rule out compression. I can tell you that all along, the kick has “felt” right.

As far as timing, when the cam sprocket “O” is lined up with the “mark” and the crank (stator) is lined up with the “T” mark, both valves are closed. When I move the crank to where the cam sprocket “O” is at 6 o’clock and the crank (stator) is at the “T” mark, the exhaust is open. Is that correct?

When you say that the stator looks off by 100 degrees – how are you “seeing” that?

Thanks for all the input - I feel I've got to be getting close!

 

[milesoffun]

Put the points back in and I'm checking the valves - when my timing light goes off, my intake valve is closed (loose tappet) and my exhaust valve is open (tappet not loose). This is when I have it set on the predefined timing "mark". This is back to where the "F" mark is still about 70 degrees away from it's "mark". I cannot make an adjustment that will get it much closer. So, does this mean that she is not firing because the exhaust port is open when when she sparks?

 

[johnnyvee]

Lets start by following the various elements as the engine goes through the 2 rotations ( 1 rotation is 360 degrees, 2 is 720) that make up one complete cycle of the four stroke engine. You can see this graphically in the GIF I posted previously. Starting with the piston at Top Dead Center (TDC) and on the power stroke here's what should be happening.

0 degrees: Both valves are closed, spark has fired at approx. 5 to 15 degrees previously, gas vapor is combusting, creating pressure, piston starts downward travel.
180 degrees: Piston reaches bottom of stroke, exhaust valve opens for exhaust stroke
360 degees. Piston reaches top of stroke. Exhaust valve closes, intake valve opens for intake stroke
540 degrees Piston reaches bottom of stroke. Intake valve closes for compression stroke.
705 to 715 degrees Spark fires BEFORE piston reaches top dead center at 720 degrees, how much depends on spark advance, which depends on RPM of engine. But NOT 70 or 100 degrees.

I came up with 100 degrees from the picture of the stator you attached. I assume that this was positioned when the spark fires?

What you said about the valve timing sounds correct. At TDC - Power both valves should be closed. At TDC - Exhaust the exhaust valve should be just closing, and the intake valve should be just opening. This 360 degree TDC - Exhaust position is the easiest place to see, because so much is happening. 0 degrees, TDC - Power is difficult to see if it's a bit off, because both valves are closed for 180 degrees of crank rotation to either side of this point.

Did you verify that the piston physically is at Top Dead Center when "T" aligns with the index mark?

Is it possible that the camshaft was 180 degrees out of correct position when the camshaft sprocket was attached?

Is it possible that the points assy. is not correct for that engine?

 

[milesoffun]

Thanks for the detailed instructions. Here is what happens for me:

First, I can verify that I'm at TDC by making sure both valves are closed and then looking at the piston in the cylinder when I have it lined up with the T mark and move the crank slightly counter clockwise and the piston starts to head down.

At 0 degrees - both valves are closed
At 180 degrees - piston is at bottom of stroke and exhaust valve is open (tappet tight)
At 360 degrees - exhaust valve is starting to close - intake valve is starting to open
at 540 degrees - intake starting to close

So this looks like what you would expect, I think.

However - this morning I was looking at a timing video and noticed I had been trying to set the timing when my test light went off, not on as I think is correct. Stupid! But glad I noticed it! Something is still off - I cannot seem to set the points to get the light to come on where it needs to come on - my cam looks like it might have a flat spot - I don't know - all I know is I've spent couple of hours and cannot get it right.

Still no luck. The picture below is when I'm at TDC with both valves closed. I'm not giving up yet!