Valve timing question (with pics!)

[KentMoney]

So I recently buttoned up my 1981 rephased engine and had it in the chasis with the throttle hooked up, etc.. I rigged up the ignition to see if I could get it to start for the first time and I ran into problems. I was trying to kick start it and I would get some backfiring, but never could get the engine running.

I am using a Pamco and it is my understanding that there is like 16 different possible configurations for the 277 rephase. I set it up in the one that seemed correct and the aforementioned backfiring occurred. So, instead of just trying a different firing configuration (like I should have) I assumed that I probably had my cam timing wrong. So I took out the engine and set up the following:

I managed to jimmy rig a piston stop, got a dial indicator from harbor freight, printed out a degree wheel and slapped it on some cardboard.

Please tell me if I did this correctly:

Determining true TDC
First I placed the left side piston to somewhere BTDC and then screwed in the piston stop. I slowly rotated it CCW until the piston hit the stop. At this point I set the degree wheel to 0 with the pointer. Then I unscrewed the piston stop, moved the piston to somewhere ATDC, and screwed the piston stop back in. I slowly rotated the crankshaft CW until the piston lightly hit the stop, and took the measurement on the degree wheel. I then divided the difference in half and determined where true TDC was. I marked a reference point.

Determing Valve Timing (is this degreeing in a cam?)
Then I set the valve lash to .012 and made sure the cam tensioner was flush. I set up the dial indicator to detect when the valve started opening. With the refrence point I marked I found true TDC and set the degree wheel to 0. I rotated the crank CW and found that the valve started opening at ~35 degrees BTDC.

So, to me it appears that my cam timing is correct? The Clymer manual says it should open 47 degrees BTDC and apparently the factory owners manual says it should open at 36 degrees BTDC. Which should it be?

If this is the case, then I probably hooked up my ignition incorrectly?

 

[KentMoney]

OK, I just went out to double check and now my reading is coming up as ~25 degrees BTDC is when the intake valve starts to open, oy vey.


So perhaps then I am off by one tooth (in order to get close to 47 degrees, like Clymer says)?

advice?

 

[Signal]

KentMoney I have only done this twice and each time had an adjustable cam sprocket and set the cam using the left inlet lobe centres.
Without Doug Meyer’s article on cam lobe centres I would have been stumped.
http://www.muzzys.com/articles/lobe_centers.html
Using this method you should be able to work out what your present lobe centres are and how much you need to adjust. You will need to know the specs of your cam (you should have these from the grinder who rephased it).
Sorry I can’t help you with working out how much to move the sprocket when you press it back on but over at the 650 Garage is a thread that may help.
http://xs650temp.proboards.com/index.cgi?board=EngineModified&action=display&thread=319
From memory your method of finding TDC is correct.
With regard to the ignition I have no experience with the Pamco system and cannot comment.

 

[KentMoney]

Thanks Signal,

The cam I have is a Mr. Riggs rephased 447 (late style cam), so the lobes should be OEM spec. So what are the numbers for the 447?

In the mean time, any other additional info is appreciated from anyeon.

 

[Signal]

Bob Bertaut has worked out the actual specs for a stock 1980 cam and generously posted them on his website.
http://www.650motorcycles.com/isky.html

 

[KentMoney]

OK, I looked again at the Clymers manual and in the back it has the specs for the 1980 models and intake opens at 36BTDC and closes 67ABDC. So what valve lash do I use to degree in the cam?

I am not sure how you relate the lobe center to the crankshaft. Should the lobe center be pointing directly up? I dont understand.

 

[KentMoney]

Bob Bertaut has worked out the actual specs for a stock 1980 cam and generously posted them on his website.
http://www.650motorcycles.com/isky.html

ah, OK. So is it saying that when the crank is at 8 degrees BTDC, I should have a reading of .050" showing on the dial indicator, being that the valve has lifted .050"? Should the valve lash be set to zero?

 

[grizld1]

For inspection valve lash, refer to the factory service manual at www.biker.net . To find TDC, rotate to your piston stop CCW and read the degree wheel. Then slowly rotate CW and read the degree wheel. True TDC is the midpoint between these two readings. For example, if your first reading is 10* BTDC and your second reading is 20* ATDC, move your pointer to read 15* off TDC in both positions. TDC will now be at the 0 mark.

Degreeing in the cam to the lobe centers usually involves altering the spec valve events, due to grind error. Refer to www.muzzys.com/articles/lobe_centers.html . Calculate lobe centers as installed, then play with the formula to determine where valve openings/closings need to occur to arrive at the spec lobe centers.

 

[Signal]

Read Doug Meyers article. I printed it out so I could read it at smoko time at work and have it next to me while I worked on the engine. I also had a pencil, paper and calculator. At first reading the article on cam setup using lobe centres looks difficult, but it’s not really.
Don’t get hung up yet on the opening and closing events, they are hard to measure as Doug explains in the second paragraph.
Bob Bertaut has the lobe centres listed if you scroll down on that link.

 

[KentMoney]

yah, so am I interpreting Bob's specs correctly? He says his measurements are at 0 lash. he says that at 8degrees BTDC that the valve should be lifted .050", right? I did this measurement but I had .050" valve lift at about 6.5 degrees BTDC. So I am off by 1.5 degrees? Is this significant at all?

Also, he says that at about 95 degrees BTDC you have .002 valve lift. So isn't he basically saying that he valve starts to open at 95BTDC? Whats up with that?



So here are the cam specs from the 1980 Owner's Manual on biker.net

So it should open 36BTDC and close 68ABDC. Also, it says nothing about lash.

So, I just remeasured one more time with .012 lash and my intake valve is opening 25BTDC and closing 61ABDC. This is 11degrees and 7degrees off, respectively. So my cam isn't symmetrical?

I then remeasured again but this time with .001 lash and I got 36BTDC and 70ABDC. This is within spec, right?!

SO WHAT THE HECK! Is my timing right or not?

 

[grizld1]

When you get readings that don't repeat, you need to check a few things. First off, reconfirm that the zero mark is still at TDC; it's easy to nudge the degree wheel and/or pointer out of position. Then take a little alcohol (never oil!) on a clean rag and be sure the indicator stem is clean and the stem is moving freely. Finally, make sure that flex in the mount isn't causing grief. A setup that might help you is to bolt a piece of flat stock to a head stay hole and bolt the last rod of the indicator holder through the flat stock--very rigid.

 

[KentMoney]

I made sure all the aforementioned suggestions were followed. I am getting the same readings in that post above yours.


What is really affecting my readings is the valve lash....

 

[mrriggs]

Ditto what Grizld1 said, repeatability is vital. In addition, make sure the degree wheel is perfectly centered on the shaft and secure.

It is difficult to get accurate opening and closing readings because it will vary based on valve lash and indicator accuracy. Setting the came based on lobe center is more repeatable (accurate). I checked the opening and closing events for my cam at 0.010" intervals from 0.010" - 0.070". The opening and closing events were all different (duh) but the lobe center calculations for all settings, except 0.010", were within a degree from each other. The readings at 0.010" were all over the map because of the "quiet ramps" on the cam. That is why the manual says to set the lash to 0.012" when checking valve timing, so the valve won't start moving until after the ramps. I prefer to use zero lash since it's easier and repeatable. With zero lash, ignore any readings under 0.020" lift.

I gave a brief explanation of lobe centers in the e-mail but I will expand on it here. The lobe center is the point where the valve is at max lift. Measuring this directly is difficult so we calculate it from the opening and closing events. Using your numbers above;

Add the opening and closing events together, 25 + 61 = 86

Add 180 to find the duration, 86 + 180 = 266

Divide duration by 2, 266 / 2 = 133

Subtract open/close even closest to TDC, 133 - 25 = 108

So your intake lobe center is 108 degrees. The spec for the 447 cam is 106 so you are 2 degrees retarded according to your first test.

in your second test you had;

36 + 70 = 106

106 + 180 = 286

286 / 2 = 143

143 - 36 = 107

107 is one degree retarded from spec and pretty darned close to what you got the first time despite the different setup and readings.

I'd say you are good to go. You could spend hours resetting the cam sprocket and not get it any closer than that.

 

[cros36]

holy shit my brain hurts...carry on.

 

[KentMoney]

holy shit my brain hurts...carry on.

LOL. this shit was confusing as hell to me at first, but it's actually fairly straight forward.



OK Mr. Riggs, so it looks like it wasn't my valve timing but perhaps the way I set up the Pamco that caused the backfiring.

When I get home I will take one more measurement with 0 lash and I will make sure my numbers are from about .030 lift. I will report back.

Thanks again.

 

[KentMoney]

So I just did it again and got 14 BTDC and 48 ABDC when looking for .030 lift of the valve. The lash is 0

14+48=62
62+180= 242
242/2 = 121
121-14 = 107

Alright. I think im gonna go ahead and button this bad boy back up.

Any other comments?

 

[grizld1]

Yep. Should have mentioned this, but when degreeing in the stock cam using spec. lash of .012", it's a good idea to check what the feeler gauge tells you by setting up the indicator on top of the valve adjuster. If the valve stem is cupped a little a feeler gauge will read the edge of the cup rather than the actual contact point, and you'll wind up with a valve lash setting that's wider than the thickness of the gauge.

 

[KentMoney]

oh dear, yet another nuance to be careful of.


I want to thank you guys for your guidance through this. I got the head torqued back down and got the engine back in the chasis.

ONWARDS!

 

[Jimmy650]

Kentmoney, I also recently put my 277 motor with pamco back in the frame and have experienced some backfiring thru the carbs when kicking, but it just won't run. Also thought my cam could b out or I had installed the ignition wrong. Did u get your bike to run? If so what worked? Any help much appreciated

 

[KentMoney]

yes, i eventually got my motor running. After doing all of the above to make sure my cam was degreed properly, it turned out that it was OK the whole time. The problem was that I had actually installed the PamCo wrong.

so, before you go ripping the engine outta the frame to check the cam you should try the second rotor position for the pamco and see if that works. keep in mind that the first magnet pass turns it on and the second magnet turns it off, I believe. so keep that in mind as you visualize the firing order when setting up your pamco.

let me know if the other rotor position ends up fixing the problem.

Kent