cam lined up?

Hey guys,

so this may be a silly question, but as some people may know i bought a replacement cam and it turned out to be the wrong one. so ive had the 1977 36tooth cam gear swapped and pressed onto the earliar lumpy cam and its ready to be reinstalled. my issue is when i removed the prior cam the crank may have moved. so how do i know where to or how to set the new cam gear so it runs in sync with the crank shaft. does this make sense?

You want the left cylinder at TDC on the compression stroke. Timing mark at TDC. Both valves would be closed at this position. And the timing mark on the cam at the 12 o'clock position, the 2 dots at 3 and 9 o'clock.

littlebill31;

Your description for the left valves (closed) seems wrong to me.

Both pistons at TDC. Left side cam lobes should be up, meaning left valves would be open on exhaust and intake. Right side cam lobes should be down. Index mark on the left side of the camshaft would be straight up at 12:00. Punch mark on the right side of the camshaft gear should be exactly even with the top surface of the head (09:00).

The large pin on the right end of the camshaft should be straight up at 12:00.

That what it says in the book. Page 61 Haynes manual.

baldyforks said:

Hey guys,

so this may be a silly question, but as some people may know i bought a replacement cam and it turned out to be the wrong one. so ive had the 1977 36tooth cam gear swapped and pressed onto the earliar lumpy cam and its ready to be reinstalled. my issue is when i removed the prior cam the crank may have moved. so how do i know where to or how to set the new cam gear so it runs in sync with the crank shaft. does this make sense?

Click to expand...

Just did mine on Sunday - I used this: http://www.650motorcycles.com/CamTiming.html

Piece 'o cake

Huh, 650motorcycles says open, Haynes says closed. Gotta love it.

None of that matters. All 4 valves will be closed until you install the top cover that holds the rockers. Even then, all valves should still be closed because you should have the rocker (valve) adjuster screws way loosened up so you're not forcing a valve open while trying to install the top cover. Just set the motor at TDC, that's the important part.

The Haynes manual was written by humans and humans make errors. I have found other errors in the Haynes manual, especially in the wiring diagrams.

None of the above signifies, since you have pressed a different sprocket onto the camshaft. You need to degree in the cam. This is done by mounting a degree wheel and pointer and finding TDC with a plunger-type TDC locator, setting the degree wheel so that the same amount of drop either side of TDC results in a reading of equal degrees BTDC and ATDC when the pointer and degree wheel read "0." You next set the valves to inspection lash, not running lash. For the 256 cam you're using, that's.012" for both intake and exhaust. The next step is to set up a dial indicator on top of a valve spring retainer with the shaft of the indicator running as close to parallel with the valve stem as you can get it. With the camshaft installed as described in the posts above, your intakes should begin to open at 47* BTDC and complete closure at 67* ABDC, and exhausts should begin opening at 60* BBDC and finish closure at 41* ATDC. Due to variations in grind, wear, etc., there'll be some variation. One approach is to calculate lobe centers for the spec. cam, then calculate where you'd need to time yours to match the lobe center specification. Most tuners give priority to the intakes, and as you're using a very forgiving OEM cam, you wouldn't go wrong with that. See the Megacycle web site for the calculations.

To correct cam timing, the sprocket must be moved. To figure out how far to move it,
measure the diameter of the sprocket boss on the camshaft and calculate the circumference of the boss from that, then divide by 360. The result is the distance, measured at the camshaft boss, that the sprocket must be moved to change valve timing by 2* (1* at the cam=2* at the crank). When you know how far and which way to move the sprocket, lay a feeler gauge of the correct width along one side or the other of the timing notch on the camshaft boss, and punch or scribe the sprocket. Align the corner of the notch with that mark.

And before anyone asks, no, I don't do pictures. There are some that may help in the DIY section at www.650motorcycles.com .

WHOA, thats pretty intense. i had to read it twice before i started to understand. dam nothing is simple. well if it doesnt line up first time im buying a new normal cam.

cheers guys. will let know how it goes

You can't be more than 1 tooth off when you line up the notch, but bear in mind that with a 36-tooth camshaft sprocket, 1 tooth=20* at the crank, and you won't really know where you are unless you inspect. The procedure is a lot less intimidating when you get your hands in it than it sounds when you read about it. Tip: if you wind up with a motor that's dead down low but wants to run like depravity cut loose and yank you right through the redline when rpm's get up a bit, your valve timing is a bit retarded. If it's just down on power no matter where you are in the rpm range, valve timing is probably too far advanced.

Valve timing error is one reason many of these engines don't develop the power they should. When you raise the deck, the camshaft position changes and valve timing advances. Aftermarket gaskets from Athena and Mike's XS are .013" thicker than OEM gaskets--enough to have a significant effect. It's worth the time and trouble to dial things in, and you'll come away with a better understanding of your motor as well.

Griz, I'm afraid this is waaaaaay above what most here are capable of, even me, lol. I acquired a 256 engine several months ago and would love to try the cam in my 447 motor. Couldn't I just mark the position of the cam notch on the 447 cam sprocket and press it onto the 256 cam so it lines up with that notch?

LOL, I understand that, but live too close to a custom engine shop to do this myself. I'll stick with stock.

thats all i did 5twins. well its all back together now. just got to sort out a few little things and im ready to see if she starts. fingers crossed

5twins, that may get you close, but there are two problems. First off, there's error due to the different tooth count. Second, valve timing differs between the two camshafts. No matter where you put the sprocket, you'll wind up with <20* error when you line up the camshaft, but how much less is up for grabs. Valve timing doesn't have to be spot-on at factory spec; even on competition cams with fast ramps, race tuners will tweak the timing up to 3* one way or the other, depending on where they want the motor to develop peak power, and the slow ramps of the OEM cams cut you a little more slack. As a WAG I'd put the chances that the sprocket would wind up in a decent operating position without measurement at around 25%. The problem is that unless you degree the cam on the bench, you won't know if you've hit the sweet spot until you have the motor back in the frame. I don't like those odds.

You're definitely capable of degreeing in a cam, and so is anyone here who's able to assemble a motor. Like many procedures, it sounds much harder than it is. The most difficult part is to keep camshaft and sprocket aligned with your marks while pressing the sprocket on. I don't even attempt that myself; it takes my machinist several tries to get it.

BTW, I gave the drop-indexing method for TDC location on the assumption that an assembled engine was being inspected. If the head is off, the best method is to locate TDC with a dial indicator set up directly on top of a piston and zero the wheel and pointer to that. Tips: Rotate the engine with the primary cover off using the nut on the right end of the crankshaft, to avoid disturbing the degree wheel. Also, if you use drop-indexing with a plunger, make sure that the cylinder is on the compression/power cycle to keep from fouling the plunger in the valves, and keep the plunger freed up by hand when the piston is on the rise. If you don't, side load will lock up the plunger.

baldyforks;

I suspect your engine will run just fine when you start it (unless you have other problems i.e. carbs, ignition, air leaks etc.) . However, grizld1 made some good points. Depending on who did the camgear swap for you, you may not realize the power gain that one wants from a "hot" cam. But hey, if you want power, what are you doing riding a 50 HP bike

50 hp? RG, you're an optimist! Those horses were counted the old way, off the crank with no alternator or drive train bits attached and what reaches the wheel is quite a bit less. And remember that saying from the old days? "Those are Japanese horses, they grow 'em small."

Anyway, baldyforks, I hope you got lucky. If not, I'll walk you through the procedure if you want to have a go at it.

grizld1 said:

You're definitely capable of degreeing in a cam, and so is anyone here who's able to assemble a motor. Like many procedures, it sounds much harder than it is. The most difficult part is to keep camshaft and sprocket aligned with your marks while pressing the sprocket on. I don't even attempt that myself; it takes my machinist several tries to get it.

Click to expand...

+1 Degreeing a cam is not difficult and should be done any time you install a cam, whether you changed the sprocket or not. You can get an inexpensive dial indicator from Harbor Freight or Enco, and print your own degree wheel. http://www.tavia.com/free_degree_wheel.html

An easier way to install the sprocket is to heat it up in an oven, or with a torch, then simply drop it onto the camshaft. If you are quick, there is plenty of time to line up the marks exactly before it shrinks on there.

Yeah griz, I try to be an optimist. I don't even have 50 hp at the motor. In Calgary we're at 3400 feet ASL. That means I only get about 45 hp If I ever get over to the ocean in British Columbia, I suspect that full 50 hp would pull my arms right out of the sockets.

cheers grizld1 ill keep that in mind and thank you to everyone else. i had a engine rebuilding shop change the gears over for me so i doupt id do a better job than them. just have to wait and see once i get everything else sorted and back on the bike.as i dont understand half of what you are all talking about. I certainly didn't do this for any evtra power, just trying to make the most of a wrongly desrcibed ebay item. cheers guys