Cam Chain - Check if TDC is Correctly Set

[Paul Sutton]

While setting up a new Boyer Bransden ignition I found I could not match TDC and the full advance settings as per the installation instructions. It has been suggested to me that the timing chain may be out by 1 or 2 teeth.

Is there a way to check the timing cam position relative to TDC without pulling the engine and physically looking? I have confirmed that the crank TDC marking matches with the pistons at TDC.

I noticed that on the right hand side of the camshaft where the ignition advance mechanism fits there is a hole drilled for the locating pin. Does this pin hole correspond exactly with the cam alignment mark? A google image search suggests this to be true but I could not get a clear enough image to be 100% sure.

When I set the crank to TDC the pin hole on the right hand side is in a true vertical position.

Thank you for any advice you can offer me regarding the alignment of this pin hole as a check on the camshaft setting.

Thank you all and have a very enjoyable festive season.

Note:
In thread "cam alignment w/ pamco" XSLeo said "Yes, the tensioner will change that cam position slightly. As the tensioner applies tension on the chain it pulls any slack in the chain to the rear of the engine. This pulls the cam backwards a bit.
With the timing marks at TDC look at the other side of the engine, where the stock advancers is. The pin that aligns the advancers up on the cam should point straight up or down. Depends on which cylinder is at TDC.
If off one tooth, the pin will be off by 10 degrees. If you imagine clock face around the advancer and the pin should be at 12:00, if off by one tooth that would have the pin at either 2 minutes before or after 12:00."

Thank you XSLeo.

What a dope I am, I should have searched better before jumping for the New Thread button.

Wishing You all the Merry Christmas - Paul (Dope)

 

[5twins]

Yes, it's easy to check by looking at the pin hole in the cam.

 

[Paul Sutton]

5twins, thank you for that link which means I am OK. Thank you everyone who has given information in the other threads I have read.

 

[5twins]

Leo mentioned the cam chain adjuster pulling the cam backwards a little and throwing the pin hole alignment off. That will only happen in the case of an extremely worn and stretched chain. If you do see that, you need a new cam chain. But that's something you just normally replace if you ever go into the top end. They can and do last many tens of thousands of miles if they're properly cared for. But that's the problem, most weren't, not checked and/or adjusted frequently enough. I've gotten into the habit of looking at mine at every oil change, so that's like every 1000 to 1500 miles. It only takes a minute to pop the cover nut off and observe the plunger movement as the bike sits there idling, and you have to run it anyway to warm the oil for changing.

 

[grizld1]

Paul, you don't use the TDC mark to set up the Boyer ignition. You get the timing close enough to correct to start and time the spark at full advance. The hole-and-paint-mark static timing (see Boyer installation instructions) is also done with the crank at 40* BTDC--again, at the full advance mark. The hole-and-paint-mark drill is very inexact, and sometimes you'll get close enough with it to start and sometimes you won't. Here's a bit of treachery. Remove your spark plugs and ground them solidly on the cylinder head. Connect your timing light, turn on the ignition, keep the button/trigger down on the light, turn the crank slowly, and look for the light to flash. Set the timing plate so that the flash happens close to the retard timing marks--not at TDC. Retard timing doesn't have to be spot on, just close enough to fire. If the light doesn't flash at all, turn the pickup clamp upside down, and if it still doesn't flash, try the other plug wire. Once the motor has started, rev it up to full advance (reached when the rotor mark no longer appears to drift left) and dial in timing to the leftmost mark (all breaker point models) or the rightmost edge of the slot in the cover (TCI models).

 

[Paul Sutton]

Grizld1, I have checked that the TDC mark is correct and I know this corresponds with the pistons at TDC. I believe everything is correct for the installation. Because the XS SH does not have a full advance mark I have used the center of the drain groove on the polished alternator side cover as per Pamcopete's recommendation. I have checked this with a strobe before making the conversion and also calculated the position using trigonometry and all methods agree. With the crank set to full advance and the paint dot positioned as per the Boyer instructions the engine was very difficult to start and ran roughly for only short bursts. I slapped the strobe on and found the Boyer firing at close to TDC. The full adjustment from the PCB brought the timing close to the right hand idle mark. I then shifted the Boyer magnetic rotor anticlockwise a bit and was then able to get the full advance to match the 40 degree position. The motor is running well and the timing is stable. Now when I manually line the paint dot up with the hole in the PCB the timing line on the alternator rotor suggests a full advance of about 60 degrees, but I know from the strobe it is actually firing at 40 degrees.

I was expecting the paint dot alignment to be perfect but as you say from experience the dot method is inexact. Conclusion, I am happy with the ignition now that I understand the inexact nature of the paint dot method and have taken the bike for a blast and all was well, smoother ride, good stability on the strobe light and clean plugs.

Thank you for all comments and the years of experience everyone brings. Must go turn the oven on for Christmas Dinner.

 

[Paul Sutton]

Having pissed some off and cause some confusion I have decided to use photographs to show exactly were my difficulties with the Boyer Bransden ignition lie:

Step 1: Based on sound advice I have explored the possibility of the cam chain being out by a tooth or two. Based on the position of the pin on the RH side of the cam, the position of the pistons and the TDC crank marking I conclude all is well in this respect.

Step2: The XS SH has different timing markings compared to older models. The markings are not cast in but are stamped into a small steel plate which is screwed to the alternator.

Because the SH has electronic ignition no marking was provided for full advance. But full advance does align with the center of the drain groove seen directly below the socket. This information came to me via this forum and I checked it prior to the Boyer installation using my strobe light and also confirmed its position by calculating the cord length from the TDC mark using trigonometry for 40 degrees advance.The following photo shows what I am taking as full advance.


Step 3: The Boyer system comes with a small magnetic rotor that mounts in what is the points compartment. This rotor has two very weak magnets set at 180 degrees to each other to activate the pickup coils.

Only one magnet is visible in this shot. The 8mm threaded rod passes through the camshaft where it uses the bushings to center it and is then locked in place on the RH side with a nut. Each magnet is marked with paint spot to assist in setting the timing.

Step 4: In front of the magnetic rotor fits a PCB with two sensor coils.

In this photo the shiny circle in the center is the end of the 8mm threaded rod. Below this circle and in line with the lower pickup coil is the inside end of one magnet. The other magnet is hidden in this photo due to the angle. The cloth is there to prevent anything falling into the spark plug hole as suggested in a video on Youtube - Thank you Peanut. To the right of the top pickup coil is a small hole drilled in the PCB and the objective is to center the paint spot on the magnet in this hole with the timing mark manually set at full advance.

Step 4: I set everything up as specified by the Boyer instructions with the paint spot in the center of the PCB hole at full advance and ensured the coil connections were all good and secure. On the XS SH the old coil connects via a two pin connector. The Red/White wire is the power from the ignition switch and the orange wire goes to the stock electronic ignition. I clipped a female spade connector to the Red/White wire and used this to power both the new coil and the Boyer ignition box. The ignition box mounted nicely against the flat surface created by the indicator and the auto cancel units and was secured with the two plastic ties provided.

When I tested the system the engine responded very very poorly and would only run for very short bursts. I slapped the strobe on and found the ignition was firing at close to the TDC mark on the timing plate that is screwed to the alternator.

Rotating the PCB, which allows some degree of retard or advance, moved the timing close to the RH idle mark as viewed with the strobe.

I then unlocked the Boyer ignition magnetic rotor and moved it slightly, relocked the nut on the RH side of the chamsaft, and was able to get the timing mark to line up with the full advanced mark (i.e. the center of the drain groove in the LH side casing - see Step 2) when viewed with the strobe.

Step 5: I took the bike for a blast and all seemed fine. Now here is the issue - When I manually rotate the crank anti-clockwise with a socket to align the white paint spot in the center of the hole on the PCB the timing mark is now set at about 58 degrees advance. (The reality is that the strobe shows the ignition fires at the correct advance position i.e. 40 degrees advanced).

See how the timing line, highlighted with white, is further advanced from the full advanced position (drain groove) to about 58 degrees.

Step 6: This last photo shows the position of the magnet relative to the hole in the PCB when the timing mark is aligned with the 40 degree advance position (drain groove). The camera angle has distorted the shot but the edge of the magnet falls right at the center of the hole. The Boyer instruction say the paint spot should be visible at the center of the hole, it is not!


My concerns: Do I have a real issue with the misalignment of the paint spot? Should it absolutely lie within the center of the PCB hole? Or is the paint spot only there as a means to get the engine to fire initially before refining the position using a strobe light?

Thank you for your time and I hope all is clear.


Added Note: That extra 18 degrees on the crank corresponds with 9 degrees on the camshaft. As there is easily a 1-2 degree error in my measurement this 9 degrees at the camshaft more than suggests the cam chain was fitted out of place by 1 tooth. I will proceed with the strip down and address valve seat grind, valve stem seals at the same time. We live and learn, often the hard way!

 

[grizld1]

Paul, forget about the paint spot! It's often off by as much as you describe, not even close to visible with the ignition correctly timed. BTW your math is backward, my friend. The cam turns at 1/2 crank speed; 18* at the cam=36* at the crank. 1 tooth at the cam=20* error at the crank with your 36T cam sprocket. Relax! Your motor wouldn't run well enough for the bike even to be ridden around the block if cam timing were out even as much as one tooth, let alone two. If you want confirmation, refer to the engine section of the service manual (available as a free download from www.biker.net) and set up a degree wheel and pointer on the crank and a dial indicator on a valve retainer. Have a fine and worry free Christmas!

 

[Paul Sutton]

I think we are saying the same thing here? My 18 degree mismatch at the crank gives a 9 degree mismatch at the camshaft.This suggests the camshaft is moved out of sync by 1 tooth. My brain is fading, been a long day. Must make more careful measurements on the cam vs TDC tomorrow but yesterdays results looked convincing to me. Perhaps I am just trying to wish the cam chain is correct when it isn't.

Note: I will call Boyer on Wednesday and get their opinion. But there reputation in the UK suggests to me that if they say the dot is in the circle then it is!

 

[peanut]

the paint spot on the Boyer magnetic rotor is not the issue . It is in exactly the same place as it has been for probably over 20 years.

The problem here has to be that the crank is not correctly aligned with the camshaft

The image of the stator and TDC marks is completely illegible so is little help in confirming anything unfortunately.

When the stator and rotor are not clearly marked its essential to go back to first principles and verify TDC. Set pistons at TDC then mark the rotor and stator with a fresh clear TDC mark. Then either use a timing disk or a protractor and laso mark the idle advance and full advance marks . Then check that the alignment mark on the camshaft sprocket is vertical at 12am .

When this is done the white spot on the Boyer magnetic rotor will line up with the hole on the pcb plate which will ensure that the boyer micro digital unit will produce a spark at the correct time and correct advance throughout the rev range.

 

[grizld1]

Right, Paul, my reading was backward, not your math! But still, if your motor runs well enough to ride, cam timing can't be off a tooth. Re. the paint mark, I've done over half a dozen BB installs over the years on my own machines, and the paint mark was sometimes out as much as described after the ignition was set with a strobe, with no adverse effects. BTW misalignment of the paint mark can't result from misalignment of cam with crank. The ignition trigger rotor is positioned in the camshaft anywhere it needs to be to fire in relation to the crank. You could be a full tooth out on valve timing and it would have no effect on the alignment of the trigger with the timing plate; you're installing the trigger to line up with the plate, not with the camshaft lobes.

 

[Paul Sutton]

Here is a better photo showing crank at TDC. I have cleaned up the markings a bit better. Notice the absence of a full advance line which if it were there would line up with the drainage groove at the bottom.

 

[Paul Sutton]

Grizld1, out of interest what would be the effect on valve timing if the camshaft is out by 1 tooth. Would this 10 degree shift prevent the engine running? Also, if the camshaft is out by one tooth would I be able to detect this with a feeler gauge, isn't the maximum gap when the engine is at TDC?

Thank you for your thoughts.

 

[grizld1]

Paul, a 1 tooth error is 20* at the crank, and no, the motor won't run with 20* valve timing error. I'll say it again--you couldn't get the motor to take you to the street with that condition. Re. valve action: at TDC, one cylinder is entering the power stroke with both valves closed, and the other is entering the exhaust stroke, with both valves open. A feeler gauge won't tell you anything useful.

 

[peanut]

You can check the correct indexing of your crankshaft to your camshaft at TDC without removing anything from your engine.

Remove the advance (cover RH side ) and look for the pin hole in the end of the camshaft which should be vertical ie 12 oclock or 6 o'clock with the crank at TDC

Here is the only image of the end of a cam I can find but it does show the pin hole at 1'oclock as the camchain was 1x tooth out on this particular engine.

Despite what has been said a xs650 engine can start and run with the timing way off .

When you look at your Boyer pcb board which hole are you using to align with the white dot on the stator magnets. The right hand or left hand hole ?

 

[650Skull]

Peanut..........Go back and read the link at post #2. Shows the Pre 1980 cam and post 1980 cam showing the TDC index hole.

 

[grizld1]

OK, Peanut, let me clarify--with a 20* error in valve timing, an XS650 motor is going to run so badly that no sane person is going to want to abuse it by putting it on the street. Paul wrote, "I took the bike for a blast and all seemed fine." Do you really think things would seem fine with valves timed 20* off, even to the least experienced rider?

 

[peanut]

Peanut..........Go back and read the link at post #2. Shows the Pre 1980 cam and post 1980 cam showing the TDC index hole.

I didn't see that link Skull but I wasn't aware of this thread when that link was posted...I should have checked the link before posting.

.Paul the PO has been PM'ing me about this issue for a week now. He asked me if it was possible to index the crank and camshaft without stripping the rocker cover off so I posted the answer on this thread for his benefit and for everyone else that comes to this thread in the future but without opening that link first

 

[peanut]

Paul, Your motor wouldn't run well enough for the bike even to be ridden around the block if cam timing were out even as much as one tooth, let alone two. !

I was commenting on this earlier statement of yours which is not factually correct

An engine certainly would start and run with the camchain one tooth out.

No I wouldn't expect anyone to run a bike whose timing was 20 degrees out but then you were taking a somewhat extreme view to emphasise your point. If a builder was trying to start and run a bike that far out they have no business building engines in the first place imo. There are plenty of manuals and online help

 

[Paul Sutton]

The PCB with the pickup coils has only one hole with a label on the back for timing and a big arrow. Some Boyer PCBs do have two holes but mine does not. The hole is a bit hard to see in the photos above but is next to the lower RH corner of the upper pickup coil.

I rechecked the TDC setting by shining a laser into the plug hole and carefully observing its position on the crown of the piston and everything looks good. I have placed a 3mm drill bit in the pin hole (very tight fit) on the RH side of the camshaft and it is vertical at TDC:

I have repeated this exercise with a small pointed and observed its position at TDC and TDC 360 degrees later:

For me this seems conclusive, the timing chain is set correctly.

Last night I was a bit worn out and did not appreciate the significance of a comment by Grizld1, but this was clear to me this morning. When I use the strobe I am setting the position of the trigger (magnets and pickup coils) relative to the crank/timing plate. This relationship is independent of the camshaft position. Even if the camshaft were out by miles the position of the magnets at full advance would still be in the exact same place relative to the PCB pickups. Of course the engine would not run with such a camshaft error but the ignition timing would be spot on. The Boyer ignition does not see the camshaft lobes, it only uses the camshaft as a convenient place to clamp the magnetic rotor.

When I started the engine after first fitting the Boyer ignition and aligning for full advance with the strobe it ran nicely without any adjustment having to be made to the idle screw. This all leads me to suspect that I happen to have a Boyer magnetic rotor that deviates a little more than "normal" and in my case the paint dots are only an initial indicator for setting the ignition. The 18 degrees I measure must just be a red-herring and coincidentally is close to what is expected if the timing chain were out of place by one tooth. In fact the 18 degrees is artificial and only arises if try to insist on the paint spot being in the center of the circle.

I must reassemble everything because the sky is blue today in South Wales, UK, and I assume this is also true for SouthWest England.

Thank you.