Topic: Cam chain timing question

[Tracksnblades1]

You’re closing in on it…
The old Hondas use a “wasted spark” ignition.
The 1/4 points fire both spark plugs of the 1&4 pair simultaneously. (Similar to an aircraft magneto, one positive spark plug, one negative spark plug in the same circuit.) One spark plug firing on a compression stroke and the other one of the spark plug pair firing at the same time on the exhaust stroke… hence the term “wasted spark”  for wasting a spark on the exhaust stroke.  2&3 points/coil  and spark plugs pair will do the same, 180* crankshaft later..

The centrifugal advance mechanism (has the points’ cam on it) and has a pin that indexes it to 1&4 crank pins. Both 1&4 crank pins are up at TDC at the same time. Flat plane crankshaft. The only way this can be off by 180* is if the low voltage (12v) point wires/coil wires are swapped or the high voltage plug wires have been swapped, or the pin has been sheared off (not likely to be 180*) where cylinders 2/3 pair would be firing simultaneously instead of 1&4’s pair..

I wouldn’t pull the cylinder head back off unless you absolutely have to…

[M 750K6]

 Can anyone explain why the slot in the end of the camshaft is the opposite side to the factory manual? Are they allmthat way? Did Honda make a change? Could it be a different cam?

[88BuckMeister]

So what you guys are saying is that every time those #s 1&4 pistons are at TC those points open and those plugs fire. Doesn't matter whether it's at the compression stroke or exhaust stroke, those points open every 360° of rotation...if that's the case then yes 100% makes sense to Mr there's no possible way to be 180° off

[willbird]

So what you guys are saying is that every time those #s 1&4 pistons are at TC those points open and those plugs fire. Doesn't matter whether it's at the compression stroke or exhaust stroke, those points open every 360° of rotation...if that's the case then yes 100% makes sense to Mr there's no possible way to be 180° off

Yep exactly on the firing :-). Pretty impressive that the points were actually twice as good as they really would need to be in a perfect world as far as not floating or otherwise acting up at whatever the highest red line Honda was.

Bill

[Tracksnblades1]

So what you guys are saying is that every time those #s 1&4 pistons are at TC those points open and those plugs fire. Doesn't matter whether it's at the compression stroke or exhaust stroke, those points open every 360° of rotation...if that's the case then yes 100% makes sense to Mr there's no possible way to be 180° off

Think you got it. That’s why they’re all making the point, it’ll line all line up the next crank revolution. 1&4 and 2&3 are each a crank shaft pair. If 1&4 is up 2&3 are down…and vice a versa…

Verify your camshaft’s mark and crank’s mark are where you want it. I like them a little advanced, they’ll always retard as the cam chain wears.  Some have filed their camshaft sprocket bolt holes a little to get it exactly where they want it..some after market camshaft sprockets have been slotted so you can advance or retard the cam a little to match up the cam cards opening and closing points.


PEWE has posted about this several times and even shared how difficult it can be to exactly match both the opening and closing events to the cam card…

[Tom R]

To answer an earlier question about how many degrees of timing per cam sprocket tooth…
Just divide 720 by the number of teeth on the sprocket. 720 because the cam is half speed of the crank. It’ll be around  15 - 20 crank degrees per tooth.

[88BuckMeister]

Ok so quick update. I took the head back off and rotated the crank a bunch of times and came back up to top center 1&4. I took pics of both the markings and the cam notch. I'm attaching those pics. Keep in mind ALL my pics are from the left side of the engine. There's tension on the cam chain so I don't see how I can be off. When the TDC mark for 2&3 is lined up, the cam notches are either straight up or straight down. When the TDC mark for 1&4 are lined up, the notch is either exactly at 3 o'clock or 9 o'clock. Tell me I've got this right, and that the confusion over the whole thing was just that the manual depicted the #4 lobes pointed upward and that's just not the case in reality...

[Mark1976]

TDC 1&4, align everything from the #4 cyl. Notch facing forward,

But that's what I did...TDC # 1&4, TC mark lined up with the case index, notch facing forward. And my lobes are facing downward. Is the manual pic just misleading?

That's how I interpreted as well.
Notch forward, lobes down, pulled out a cam.
As Scott mentioned above, once its in, turn the crank 2 full revolutions, it will align right back up where you started.

Over thinking it,
Cyl 1 tdc, notch forward, done.

[Don R]

 One time at the timing mark it fires 1&4 for #1, the next time around it fires 1&4 for #4 The coil doesn't know which one is on compression.
  That line drawing is obviously incorrect since the lobes and notch are fixed on the cam.

[Mark1976]

One time at the timing mark it fires 1&4 for #1, the next time around it fires 1&4 for #4 The coil doesn't know which one is on compression.
  That line drawing is obviously incorrect since the lobes and notch are fixed on the cam.

+1
Done.

[88BuckMeister]

Ok so I'm good then ya? #s 1&4 tdc with the timing mark lined up, and the notch in the cam @ 3 o'clock, rotated a few times and repeated with tension on the chain and it's exactly the same

[dave500]

Read the posts again……Dave…🙄

Nary once did I say the camshaft was 180* out…or could be….🙄🙄

The crank triggered distributor-less advantage I was referring to was the fact the camshaft’s timing right or wrong  doesn’t affect the proper ignition timing either…nor can it ever be 180* out of timing with the crankshaft with it being pinned to the crankshaft, other than improper wiring…🤔

i re read the posts,bucky isnt asking about ignition only the cam timing.

[Little_Phil]

Ok so quick update. I took the head back off and rotated the crank a bunch of times and came back up to top center 1&4.

Pity the posts caused you unnecessary work. The ignition cam with the 1/4 markings on it is pinned to the end of the crankshaft so it's bound to be correct.
The Honda drawing in the manual is merely showing a couple of random lobes to say "this is the camshaft"

[88BuckMeister]

Understood. Got it got it. I really just want to make sure I'm precise. The only thing creeping in the back of my mind is a thread here from like 2019 where a guy did EXACTLY the build I'm doing. Big bore kit, and a 650 cam in his 550 motor. I don't think he went with the racing springs...I did that out of sheer paranoia. But he set his idle, all was well, and the first mile he blew his #4 cylinder. Neeeeoooowwwwbody knows what happened. Keepers/valve failing was dismissed as apparently the stock components on these bikes were bullent proof. So what happened? I have theories about valve surge at high RPMs causing an interface strike which just tumbled into catastrophe, but still, that thread made me PARANOID AS HELL because I've put way too much time, energy and $$ into this motor to blow it up 😔

[bryanj]

Did he check the piston to valve clearance with clay?

[88BuckMeister]

Did he check the piston to valve clearance with clay?

Yes sir. I tried my best, first time doing it. Didn't stick super well, but I did follow the instructions as well as I could. Was told the clearances were more than sufficient. The top of the piston protrudes into the combustion chamber, but the divets and rest of the piston sit what appears to be a little lower than normal...

[Tracksnblades1]

Did he check the piston to valve clearance with clay?

Yes sir. I tried my best, first time doing it. Didn't stick super well, but I did follow the instructions as well as I could. Was told the clearances were more than sufficient. The top of the piston protrudes into the combustion chamber, but the divets and rest of the piston sit what appears to be a little lower than normal...

I think he was asking about the blown up one..

What brand of clay did you use..?  Look like it transferred really well.
I usually use the light spring indicator method, but it looks like you could get an excellent read on that type of clay.

What was the quench clearance you have showing?  With or without head gasket..?

[88BuckMeister]

Don't stone me, but I used red PlayDoh lol. I read a lot of clay options, and found one option online that said there's something about red PlayDoh that is really good for this...unopened and not old. Grabbed it from my kids play cabinet. I followed the same advise, everything very clean and oil the top of the PlayDoh and the valves. Worked like a charm. They also said if some gets trapped in your rings it won't pose any risks like some clay can. Again, it seemed to work.

I tossed the readings paperwork, but with the exhaust the lowest I had was just under .08 and the highest I head with any valve was like .125. I torqued it with a new head gasket to do an accurate mock of the actual conditions and to prevent the machined surfaces from touching each other (I was afraid the dowel pins grabbing would cause some sort of accident in the process).

[Tracksnblades1]

Don't stone me, but I used red PlayDoh lol. I read a lot of clay options, and found one option online that said there's something about red PlayDoh that is really good for this...unopened and not old. Grabbed it from my kids play cabinet. I followed the same advise, everything very clean and oil the top of the PlayDoh and the valves. Worked like a charm. They also said if some gets trapped in your rings it won't pose any risks like some clay can. Again, it seemed to work.

I tossed the readings paperwork, but with the exhaust the lowest I had was just under .08 and the highest I head with any valve was like .125. I torqued it with a new head gasket to do an accurate mock of the actual conditions and to prevent the machined surfaces from touching each other (I was afraid the dowel pins grabbing would cause some sort of accident in the process).

I see. Looks good..
Just curious what the actual squish/quench clearance was on a 550.…I like it tight….I don’t remember any 500/550 posts of the actual assembled clearances…especially with a big bore…

[88BuckMeister]

Don't stone me, but I used red PlayDoh lol. I read a lot of clay options, and found one option online that said there's something about red PlayDoh that is really good for this...unopened and not old. Grabbed it from my kids play cabinet. I followed the same advise, everything very clean and oil the top of the PlayDoh and the valves. Worked like a charm. They also said if some gets trapped in your rings it won't pose any risks like some clay can. Again, it seemed to work.

I tossed the readings paperwork, but with the exhaust the lowest I had was just under .08 and the highest I head with any valve was like .125. I torqued it with a new head gasket to do an accurate mock of the actual conditions and to prevent the machined surfaces from touching each other (I was afraid the dowel pins grabbing would cause some sort of accident in the process).

I see. Looks good..
Just curious what the actual squish/quench clearance was on a 550.…I like it tight….I don’t remember any 500/550 posts of the actual assembled clearances…especially with a big bore…

They were tighter on the exhaust. I must say the lobes on the 650 cam are ridiculously monstrous compared to the 550. I was worried about it. That's why I got the racing springs. But I think the tightest was like .075 but I hope I did it right. Playdoh is very squishy so using a caliper against it is tricky. But all in all you can visibly see the space. Should be ok.

I take that back I might actually still have the clearances. I'll post them tomorrow if I do. I know where the notepad is.

[Tracksnblades1]

Sounds good..

The valve to piston clearance can change a little as the cam chain wears (retards camshaft)  Retarding a cam usually increases piston to exhaust valve clearance while reducing the intakes PTV clearance.

And advancing a cam after initial clearance checks usually reduces the exhaust valve’s PTV clearance, while increasing the intake valve’s PTV clearance. Just the opposite as retarding it.. so your checking is done unless you plan on advancing your cam from its current setting..

Squish/quench clearance is the piston to cylinder head clearance. It shows in one of your pictures.

Squish/quench, squish can impart turbulence into the combustion chamber to aid more complete combustion...mentally picture a piston and cylinder head like the old small block Chevy. Where 1/3 of the cylinder head combustion chamber is flat. And the piston to cylinder head clearance (same as squish/quench) is established by the top of the piston at TDC and the cylinder head’s gasket thickness.Let’s say the SBC’s squish/quench clearance is perfect at a debatable.0.035- 0.038”. Now the piston comes screaming up to TDC with a 4 inch bore. As the piston reaches TDC all fuel and air mixture below this 0.035 squish area is squeezed out very quickly into the 2/3 size combustion chamber, except the “end gases” still trapped in the 0.035 clearance.

The quench part can be more of a debate, but generally it can quench (prevent) the detonation of the end gasses from the ever increasing pressure and radiated heat of the fast approaching flame front burning from the spark plug’s point of origin toward the cylinder/head gasket area of the chamber. The end gases trapped in this 0.035 squish/quench area are in very close proximity to the piston and cylinder head.  Both of which are considerably cooler than the approaching flame front (heat of combustion). Effectively preventing the trapped “end gases” temperatures to rise quick enough to auto-ignite (detonate)
As the piston moves away from top dead center these trapped “end gases” may still be more completely burnt. It’s all debatable but a small squish/quench clearance can make the engine more tolerable to lower octane fuel,with out detonation and aid in higher combustion efficiency(more power).

For example an old 4 inch small block Chevy had all the flat top pistons 0.020 down in the cylinder at TDC.
Chevrolet sent them new out the door with a 0.018 mild steel shim head gasket and barely 0.001 rod bearing clearance with a forged steel rod and a cast iron block. Both of which doesn’t expand as much as their aluminum counterparts.

After the steel shim head gasket rusted away from lack of antifreeze and coolant conditioner, most shops replaced them with the felpro blue non retorquing 0.040 thickness good for bores up to 4.125 +0.060 oberbore. Instead of using the new 4.00inch bore 0.016 or 0.018 stainless steel offerings from Chevrolet. Both of which would require retorquing. On a test drive or owner complaint of pinging even though the compression was lower. the shops would reduce the initial timing from 12* to 6* btdc. Pinging gone, owner’s new complaint doesnt run as good…

[dave500]

i used xl125 pitons in a 500 once,ended up having the combustion chambers milled out to reduce compression slightly,didnt want to run a hotter cam and couldnt control pinging,plenty of valve clearance with plasticine test,youll have no worries with a 650 cam on flat tops,dont make work for yourself.