Topic: CB550 Top End Rebuild

[CJK]

Looks to me like it would be close to spot on if on T mark

Timing plate was a few degrees before F.




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[MRieck]

I am very sorry to see this kind of damage Chris. I have to ask....did you use a piston stop and degree wheel to find TDC? Also....the cam chain tensioner was installed when you set the cam up?
The exhaust valves hitting indicates late closing valves (very retarded cam timing) especially given the fact you were using an OEM based cam. That or....as you said....the bolts were not tighten down enough. 

[CJK]

I am very sorry to see this kind of damage Chris. I have to ask....did you use a piston stop and degree wheel to find TDC? Also....the cam chain tensioner was installed when you set the cam up?
The exhaust valves hitting indicates late closing valves (very retarded cam timing) especially given the fact you were using an OEM based cam. That or....as you said....the bolts were not tighten down enough.

I’m sorry to have destroyed your handiwork without being able to enjoy it. You really did an amazing job.

I did use a piston stop and degree wheel to find TDC. Cam chain tensioner was installed and adjusted per the manual.

I guess this can be a cautionary tale to all about using an adjustable cam sprocket. The reason I didn’t install the original is that one of teeth chipped slightly when I was removing the cam chain. 

Since this wasn’t the first time it ran, only ever in neutral for tuning, I really do think the cam sprocket slipped, retarding the timing, and thus leaving exhaust valves open too long.

Do you think any of the top end parts are salvageable? I imagine the force of going from like 4K rpm to 0 rpm could cause damage to rod and crank.

[bryanj]

Look at your marks, the f is before the t so you have to turn the crank clockwise to reach tdc and if you rotated the cam clockwise the notch would be closer to parrallel.

[dave500]

im with bryanj

[MRieck]

I am very sorry to see this kind of damage Chris. I have to ask....did you use a piston stop and degree wheel to find TDC? Also....the cam chain tensioner was installed when you set the cam up?
The exhaust valves hitting indicates late closing valves (very retarded cam timing) especially given the fact you were using an OEM based cam. That or....as you said....the bolts were not tighten down enough.

I’m sorry to have destroyed your handiwork without being able to enjoy it. You really did an amazing job.

I did use a piston stop and degree wheel to find TDC. Cam chain tensioner was installed and adjusted per the manual.

I guess this can be a cautionary tale to all about using an adjustable cam sprocket. The reason I didn’t install the original is that one of teeth chipped slightly when I was removing the cam chain. 

Since this wasn’t the first time it ran, only ever in neutral for tuning, I really do think the cam sprocket slipped, retarding the timing, and thus leaving exhaust valves open too long.

Do you think any of the top end parts are salvageable? I imagine the force of going from like 4K rpm to 0 rpm could cause damage to rod and crank.

3 Intake valves and 7 of the 8 springs should be fine. 7 retainers and their keepers should be fine too. Cam should be OK as well as most of the rocker arms. The 3 pistons are probably usable .That's a tough break.....wish I had better news

[maxheadflow]

While it does look like the sprocket slipped, valve cutaways in the head are in the wrong place. Might as well not have any cut away.  These bigger than stock exhaust valves? 

[CJK]

Look at your marks, the f is before the t so you have to turn the crank clockwise to reach tdc and if you rotated the cam clockwise the notch would be closer to parrallel.

Yeah...thinking about, I agree that the current position of cam and crank doesn’t look retarded.

Also, to be clear, I’m only making an assumption that the sprocket slipped and retarded the timing, which causes the issue.

During disassembly, I was unable to rotate the crank CCW or the cam CW. The piston prevented movement that direction. In order to remove the cam sprocket, I had to rotate opposite direction. The screws on the sprocket were still tight and I don’t The any indication that the sprocket did move.


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[bryanj]

When you said you used clay to check clearance was that with everything torqued up and what clearance did you get?

[CJK]

Piston to Valve clearance completed using the clay method.

Without any HG, the Intake clearance was 0.100” across the board and the Exhaust was 0.065”.

I would assume a standard thickness MLS HG (0.040”) would be appropriate.

@bryanj - I did clay method without a HG, torqued down and valves did not touch.

I installed a MLS head gasket of 0.040” upon final assembly.


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[flatlander]

are these the minimum clearances measured, across the movements of valve and piston?
do you have the clearance at max valve lift, with cam installed and properly degrees?

[maxheadflow]

yeah if all made contact it wasn't a keeper let go,either as you said cam bolts slipped or way to close clearance?if the clearance was too close id imagine both inlet and exhaust valves would collide with the pistons,being only the exhausts id guess the timing went off,or was set wrongly?was the valve clearance to pistons checked?if only those eye brows were bigger?

I checked valve clearances with the clay method on top of pistons and they did not touch.

To set timing, I followed the manual exactly (Cylinder 1 @ TDC, cam notch parallel to head) and it ran very well in neutral when I was tuning it. This was the first time under load and it drove for about a mile before I suspect the cam sprocket slipped back several degrees, retarding the timing and sending the #1 exhaust valve into the piston.

When disassembling, this is where the timing advancer and cam notch were at. Timing advancer is a 3-5 degrees before F, the notch is probably 10-15 degrees behind where it needs to be.





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This is way off.  Think about it.  If you were 10 degrees off from TDC on the crank, you would only be 5 degrees off on the cam position.

[bryanj]

Ive built too many 500/550 engines to remember and those marks are not far out, i suspect that even though the valves had clearance at hand turn there was not enough at running speed

[maxheadflow]

Well. I've probably only had the top ends off of 5-10 cb500s/cb550s but have timed a number of other bikes (too many to count)  with chain drive cams. If you assume that the advance mech is off by 10 deg BTDC the cam should only be off by 5 deg (2 to 1 on the cam).  From the picture it's about 18 degrees and it's in the direction where the exhaust valves would hit.  There is probably some parallax error in the measurement but not 13 deg.

[maxheadflow]

Again the valve reliefs are in the wrong place and need to be moved.. Here is an example (tho a little extreme).

 

[calj737]

Again the valve reliefs are in the wrong place and need to be moved.. Here is an example (tho a little extreme).

Respectfully, if your assertion were true, both 1&4 would also strike the piston. As only cylinder 1 is damaged, it is far more likely the valve keeper failed. You would have to read Chris’ entire build to identify an error in assembly and timing. He was awfully careful building it, and with 0.040 gasket and a stock 650 cam, the valve size is not an issue, nor are the piston reliefs.

Even with oversized intakes, a stock cam, a 650 cam and even a MegaCycle 126-00 don’t require piston reliefs. Only when you get to the 126-20 cam and oversized intakes.

[dave500]

id re assemble whats left to recheck the valve to piston clearance,if it doesent look like the cam wheel slipped,i first suggested the keeper let go but the slipping cam idea was raised,the valves are closest the piston during overlap,possibly bending both valves?

[CJK]

id re assemble whats left to recheck the valve to piston clearance,if it doesent look like the cam wheel slipped,i first suggested the keeper let go but the slipping cam idea was raised.

I can do that by the end of the weekend. I’ll do the clay again, except with the gasket on top this time.

I just made the assumption it was an issue with timing, but thinking about it, the timing doesn’t look bad. If it were bad, the cam alignment notch would be above the parallel surface of the head.

I didn’t suspect the keeper slipped, but honestly I wouldn’t know what to look for there. 
Mike did the head porting and valve job and I just slapped it on top.


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[CJK]

Again the valve reliefs are in the wrong place and need to be moved.. Here is an example (tho a little extreme).

Respectfully, if your assertion were true, both 1&4 would also strike the piston. As only cylinder 1 is damaged, it is far more likely the valve keeper failed. You would have to read Chris’ entire build to identify an error in assembly and timing. He was awfully careful building it, and with 0.040 gasket and a stock 650 cam, the valve size is not an issue, nor are the piston reliefs.

Even with oversized intakes, a stock cam, a 650 cam and even a MegaCycle 126-00 don’t require piston reliefs. Only when you get to the 126-20 cam and oversized intakes.

Agree that valve reliefs aren’t in the wrong spot, when I did the piston-valve clearance check with clay, the valves were nestled into the valve seats parallel to the reliefs with the edge being within there.

Thanks for all the help thus far, Cal.


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[maxheadflow]

id re assemble whats left to recheck the valve to piston clearance,if it doesent look like the cam wheel slipped,i first suggested the keeper let go but the slipping cam idea was raised.

I can do that by the end of the weekend. I’ll do the clay again, except with the gasket on top this time.

I just made the assumption it was an issue with timing, but thinking about it, the timing doesn’t look bad. If it were bad, the cam alignment notch would be above the parallel surface of the head.

I didn’t suspect the keeper slipped, but honestly I wouldn’t know what to look for there. 
Mike did the head porting and valve job and I just slapped it on top.


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Yeah, I looked closer and the valve relief is in the right spot. I had it backwards  The red is valve contact area and green is the relief.

I still disagree on the keeper going.  Piston I show looks to be #2 and there is evidence of contact on #4 valve.  I still think the cam timing is off or it was slipping while the engine was running. I really don't care for the slotted sprockets. Not enough contact area for the bolts.

[CJK]

id re assemble whats left to recheck the valve to piston clearance,if it doesent look like the cam wheel slipped,i first suggested the keeper let go but the slipping cam idea was raised.

I can do that by the end of the weekend. I’ll do the clay again, except with the gasket on top this time.

I just made the assumption it was an issue with timing, but thinking about it, the timing doesn’t look bad. If it were bad, the cam alignment notch would be above the parallel surface of the head.

I didn’t suspect the keeper slipped, but honestly I wouldn’t know what to look for there. 
Mike did the head porting and valve job and I just slapped it on top.


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Yeah, I looked closer and the valve relief is in the right spot. I had it backwards  The red is valve contact area and green is the relief.

I still disagree on the keeper going.  Piston I show looks to be #2 and the is evidence of contact on #4 valve.  I still think the cam timing is off or it was slipping while the engine was running. I really don't care for the slotted sprockets. Not enough contact area for the bolts.

Yes, there was contact of the exhaust valves to pistons 2-3 in the relief, and #4 as you showed.

After this lesson, I don’t care for slotted sprockets, either. I used thread lock and tighten them down to spec + a touch extra...but like you said, not a lot of contact area for the bolts. If the slotting down in such a way that the most it could retard was back to stock, then it would be safer.


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[maxheadflow]

Is these any evidence on the slot that the bolts slipped?  Probably is..

[CJK]

Is these any evidence on the slot that the bolts slipped?  Probably is..

I don’t remember seeing any scratches in the bolt channel, but I didn’t look super closely. I was more preoccupied with the explosion of metal in cylinder 1


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[maxheadflow]

Is these any evidence on the slot that the bolts slipped?  Probably is..

I don’t remember seeing any scratches in the bolt channel, but I didn’t look super closely. I was more preoccupied with the explosion of metal in cylinder 1


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I can imagine.  It's got to be pretty depressing. 

One thing you need to check for is a bent rod.    The most common I've seen is that it will be bent slightly to one side.

[CJK]

Is these any evidence on the slot that the bolts slipped?  Probably is..

I don’t remember seeing any scratches in the bolt channel, but I didn’t look super closely. I was more preoccupied with the explosion of metal in cylinder 1


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I can imagine.  It's got to be pretty depressing. 

One thing you need to check for is a bent rod.    The most common I've seen is that it will be bent slightly to one side.

Thanks. I imagine the force damaged the rod and maybe the crankshaft...basically top and bottom end need to be replaced.

...at least I still have a transmission


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