looks like cam timing is out?? with photos.

[Metal]

Hi guys,
So I just put in a new stock 256 can and I'm also running a PMA. I got my self a piston TDC stop, a degree wheel and a dial indicator.

Went about finding TDC and remarking it on my PMA.

Set the valves to .012 and the went to see when the inlet valve would open. 47 degrees is what I was looking for but it begins to open at 10 degrees.

My cam chain is out right?

 

[NONclow]

The cam may be off a tooth. Where does the mark line up on the cam?

 

[TwoManyXS1Bs]

With the 256, one tooth off is 20 degrees, you might be off 2 teeth...

 

[grizld1]

Nope, do the math. The 256 sprockets are 17/34. 1 tooth=21.17*. If a 36 tooth cam sprocket has been installed for a 18 tooth 447 crank sprocket, you'd get a 20* change per tooth.

Metal, unless those valves are new, be sure to check valve lash with your dial indicator. Cupping could give you a false reading with a feeler gauge--not 37* worth of error, of course, but enough to be troublesome.

 

[NONclow]

Maybe a combination of chain stretch and off a tooth ? Still curious about that cam mark.

 

[Metal]

Ok so I lined up the cam mark and yes it looked off one tooth. problem is it looked off either way of centre I moved it. The mark falls right between two teeth and lines up with a low in the sprocket. Is this normal? Just paid 350 for the cam as 256 stuff is real expensive. I have a new chain I'm going to try that next. The valves cups look after market to me but I can't see how that effects the cam timing. I did just find out it has a 750 kit in it. Kind of nice to know. Thanks for the help guys.

 

[Metal]

Ahhh my brain hurts. If at top dead center the intake begins to open would that be due to my valve springs being incorrect?

So far my huge timming issue can only be due to a small list of things
1. The sprocket is off by 1/2 a tooth which would only account for 10*

2. This engine had a big cam to go with the 750 kit before I swapped it out for a stock 256 so maybe the valves are different?

3. I have rockers out of a late engine in my 256 and they are not compatible ?

I'm really lost as to why it won't time up as per the manual.

Help I'm so lost

 

[NONclow]

 

[TwoManyXS1Bs]

Do you have 447 18-teeth or 256 17-teeth crank/sproket? Does the cam have 256 34-teeth, or modified for 447 36-teeth? They gotta match...

 

[Metal]

Not sure about the crank but I took a 256 34 tooth out and put a 256 34 tooth back in so I think I'm good.

 

[grizld1]

Just to be clear--if your inspection valve lash is off, readings from your degree wheel will be off. If the valve stems are cupped, your feeler gauge will read the edge of the cup, your adjuster will contact the bottom of the cup, and your valve lash setting will be wider than what the gauge tells you.

 

[hotdog]

Not sure about the crank but I took a 256 34 tooth out and put a 256 34 tooth back in so I think I'm good.

Sorry guy but you need to be sure...if your running a 447 crank sprocket with a 256 cam - it aint gonna work & vise vesa. You need to confirm you have a 256 crank sprocket or install a 447 cam sprocket if the crank is 447.

Looking at your engine, it looks like a 256 due to the 3 bolt exhaust inspection cover.

 

[XSLeo]

The 3 or 4 bolt valve cover won't tell you much about if its a 256 or 447. The 72 and 73 were 256 engines that had 4 bolt covers. The 4 bolt covers came with the e-start not the change from 256 to 447.
The best way is to look on the rods they have the 256 or 447 printed right on them.
It having a 750 kit some one may have converted it to 447 crank rods and pistons. If you didn't build it you don't know just what did happen.
On the cam you took out did it have a 34 or 36 tooth sprocket?
Leo

 

[hotdog]

The 3 or 4 bolt valve cover won't tell you much about if its a 256 or 447. The 72 and 73 were 256 engines that had 4 bolt covers. The 4 bolt covers came with the e-start not the change from 256 to 447.
The best way is to look on the rods they have the 256 or 447 printed right on them.
It having a 750 kit some one may have converted it to 447 crank rods and pistons. If you didn't build it you don't know just what did happen.
On the cam you took out did it have a 34 or 36 tooth sprocket?
Leo

Exactly right Leo...my mistake. Typing without thinking.

 

[Metal]

Your right Leo, its hard to know what's in there. So I guess I'll pull it down. Only way to really know for sure.

 

[650Skull]

this thread has descended into the discussion about a 447 or 256 crank sprocket against the 447/256 cam sprocket again the same as your other thread, "Top end question'

Count the teeth on the crank sprocket through the sump, as advised in the other thread, check the sprocket on the new cam to see if it matches a 256 cam. Check to see if both sprockets match.

Question: How do you know you bought a 256 cam.

Take side on pics of all three cams, the one you took out, the ist one you bought and the last one, and post them up for a conclusion on what you have.

Vanolia made, (and still do), 256 750c cc pistons so it is not a forgone conclusion the crank has been changed to a 447. In fact get that idea out of your head and start from the beginning and confirm what you have by counting the teeth on the bottom sprocket

 

[grizld1]

Good advice, Skull. And you don't even have to count teeth on the crank to do it, all you have to do is count the teeth on the camshaft. With the head and cylinders held down with spacers and without installing the head cover, install the cam chain tensioner and rotate the motor to TDC with the notch in the camshaft boss vertical (note that it is at the top only every other revolution of the crank). Now start turning the crank through with a wrench. If the notch does not hold the same position at TDC after 15 or so revolutions of the cam (30 or so revs of the crank), your sprockets are mismatched--not geared at a 2:1 ratio. If the position of the camshaft remains consistent in relation to the crank (notch stays in the same place at TDC), you're in good shape. BTW, this is why a misgeared camshaft would lock up the motor in short order.

 

[mrriggs]

The tooth count on the sprockets are different because the chain pitch is different. You can not assemble it if the sprockets and chain don't all match.

I keep a 219 chain on my workbench to quickly check sprockets. It will wrap around a 447 sprocket but only mesh with about 4 teeth on a 256 sprocket.

 

[grizld1]

Yeah, I knew about the pitch difference and had my doubts about whether that assembly was even possible, but had never attempted to wrap the wrong chain on a sprocket to find out. Thanks for the test and the results, mrriggs!

Look, Metal, the bottom line here is that a 447 cam is going to have "447" cast into it, and a 256 cam is going to be marked "256." If you don't see markings you're dealing with an aftermarket item. Have you been over the lobes with a micrometer? If not I'd recommend it.

 

[cra-z1]

It's possible the cam sprocket has been removed and repositioned at some point. I assume it's a used cam and you do not know it's history.