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SOHC timing....please help!!

nsxguy7

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Hello all. I'm at wits end and hope someone can help me.
75 SOHC motor. Just did a stock rebuild. Head professionally rebuilt. Everything lines up as per the manual. #1 cylinder at TDC, notch on the cam pointing up, etc. I adjusted the valves on cylinder #1 no problem. According to the shop manual, you adjust the exhaust valve on #2 and the intake on #3 at the same time. No dice. On both cylinders, even with the adjustment screw backed all the way in, the rocker is sitting tight against the top of the valve stem. I've triple checked everything and I'm stumped. Please help.
 
Remember cylinder 1 is on the left as you sit on the bike...lot of people get that mixed up. If you turn to tdc on cylinder 2 are the rockers loose? You can easily just adjust the valves one cylinder at a time, just put each on top dead center. On my high performance motors I do each lobe one at a time, turn it so each lobe is on the base circle of the cam.
 
Thanks Digger. I knew you would chime in at some point. Yes, at least I got cylinder #1 right. I kind of finally figured out what you are saying. So if the notch on the end of the camshaft is at 12 o'clock when cylinder 1 is at TDC, is it at 3 o'clock when #2 is at TDC, 6 o'clock for #3, and so on? Thanks!
 
Just watch the timing mark on the crank. Turn to tdc number 1 set valves, turn half turn to tdc number 2 set valves, turn half turn to tdc 4 etc
 
Thanks Digger, I think I got it. One question- is it possible to get the timing off by 180 degrees or not? I say no, a friend says yes. Doesn't seem possible to me...
 
Yes you can get it off 180 degrees. Pull #1 plug and put your finger over the plug hole and turn motor over slow by hand until you start to fill compression from #1. You are now on the compression stroke. Now put it on TDC.
 
If the cam is off 180 it will still run fine as cylinder 1 and 4 are paired on ignition. When cylinder 1 is on compression 4 is on exhaust but both cylinders have spark as they share coil. If you left the crank at top dead center 1 cylinder 4 is also at tdc, now if you just took the cam out and put it in 180 off then cylinder 1 would be on exhaust and cylinder 4 would be tdc compression but you would still fire because both cylinder 1 and 4 get spark at same time.
 
SOHC timing - Help please

I have the same issue as NSXGUY7 - I have set the cam up twice and it is definitely in the right place - adjusting the rockers on no 1 cylinder is ok (ish) however then cylinders 2 exhaust and 3 inlet and solid - no way to adjust them with no 1 at TDC - which apparently I should be able to do according to both manuals I have.
I have now adjusted all valves independently but the adjustment screws on all the valves are not protruding from the rocker arm, almost as if the arm, not the adjusting screw is hitting the end of the valve!! It just looks wrong?!
I have fitted new valves from David Silver Spares - is there a chance the valve (ends) are slightly longer? i.e. making the available gap between end of valve and rocker smaller?
I am rebuilding from scratch so don't want to put the engine in the frame unless I am certain it is right.
My first bike rebuild although I have rebuild several cars.
Any advice would be appreciated
 
It sounds like you’re over thinking things guys:

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Sounds to me like you are not checking the clearance on the base of the cam. I have sunk the valves in the heads quite a ways several times and still never ran into an issue with not having the adjuster screws protrude from the rockers. Some more information may help. Is this a K or F engine? Any valve seat work? Valves sunk in the head? Maybe try sending some good photos of how you are doing the adjustment. The is a lot of room in the valve train area on these motors so something has to really be off to not have any adjustment room. I normally just do one valve at a time. Watch the cam lobes and adjust the valve when you are sure its on the base circle. When intake is fully open adjust the exhaust on that cylinder, then turn over, when exhaust just starts to move adjust the intake.
 
X3. I only set one valve (well, a pair on a DOHC) per crank movement too. Doing multiples should work but you can get too close to base circle beginning to move into clearance ramps to alter your setting to me. Easier for me on DOHC anyway as you get to easily see the cam lobe opposite the valve itself much clearer. I set all valves with that cam lobe as dead opposite the valve as possible by sight. The DOHC engine you are supposed to use the same multiple valve setting technique but on the DOHC it can present other problems. Honda had to change the marks to set valves once but that did no good either. The engine has other physical problems the service manuals don't address.

In my view setting 4 valves at one time on a SOHC 4 means at least a few will not be set as precisely as they could be. It's obvious the technique was developed as much to get the bikes out the door quicker to make more money for dealers as for accuracy.
 
Valve timing SOHC cb 750

Guys thanks for the reply's - I didn't do any work to the valve seats - they were fine. I have looked at photos I took before I stripped the engine and the adjusters were protruding from the rockers so I know it is wrong - just can't see where.

I have the cam in the right position with the notch at the top and in that position the two cam lobes on no 1 cylinder (left most if seated on the bike) are both slightly tipped up with the inlet valve just closed and the exhaust about to open - the cam is meant to be in this position (i.e. notch at 12.00 o'clock) for TDC on no 1 as far as I know.
The bike ran before I started to strip it down - I am doing a total rebuild of the whole bike - the photos I took of the valves before hand, although not great, show the adjusters are well into the rocker arms - not like the way it is now - sorry I can't seem to be able to add a photo?

The bike is a SOHC K1

Dirtdigger - should the cams be in this position or should they be in the 'base circle' - according to the manual - I should be adjusting just as the inlet is closing and exhaust about to open? It sound from your reply that you do the setting when the cam is at its smallest height - base circle?

Again any ideas welcome

thanks
 
But the manual says to do it with the cam at the TDC position doesn't it? I did try it like this and it seems much more like it but I wasn't sure the valves would then close properly. I will have a go again like this - but if you measure on the base circle then the cam is 180 degrees out from TDC on no 1. Unless I am reading it completely incorrectly.
I am losing the will to live over this!!!
Will try it like this tomorrow - and let you know
Thanks again
 
The manual way is having you set the valves that are on base circle. You will pretty much get the same results. You can just make darn sure when you do one lobe at a time, then you know is not slightly on the ramp. You need to post some pictures or maybe a link to the valves you installed because you must have an issue with parts or assembly. Also you said you didnt mess with the seats in the head but you installed new valves?? Old guides??
 
After rereading the thread I'm beginning to wonder how much of a problem there really is.

'...adjusting the rockers on no 1 cylinder is ok (ish) however then cylinders 2 exhaust and 3 inlet and SOLID - no way to adjust them with no 1 at TDC...'

Caps are mine. If those 2-3 valves are solid with no clearances then they were mis-set or the cam in the wrong position, likely due to the wrong TDC taken. The 'ok (ish)' seems to add to that. There are TWO TDC points on every 4 stroke engine, one is the right one you need to be working with and the other is NOT, they alternate one after the other over and over as the engine rotates. The engine should likely have been rolled over one full turn to the next TDC point. One needs to remember that the cam only turns ONE turn while the crank turns TWO, the cam turns at half the speed of the crank. If you make a mistake locating the first TDC then following the instructions of how to get to the other valve setting points will all be wrong too, the wrong TDC has the next one wrong as well. You MUST begin with the correct one.

The rocker adjusting studs are SUPPOSED to stick out the top much more than the bottom, in no way are they even. I can't really see the bottom ends that touch the valves on my 550 either, that means nothing. At least to me.
 
To know the engine is on the correct TDC then when lined up all 4 valves that set at the same time should be loose when worked by hand. If set then they will stay loose in that position. If you cannot seem to get anything but tight valve (even on only 1 of the 4) regardless of how you set (thus letting the stud tops expose more than they should) then you are likely on the wrong TDC.

If the engine is going together new then the valvetips will be off so far you won't know where they are. I would before I put on the top cover roll the engine around to the TDC point that has the #1 valve cam lobes as far away from the rocker ends as they can go, you oppose the rocker (other end) contact point by putting the base circle firmly there with lobe facing the opposite way. I would back out all the rocker adjustment tips too to be way whoppingly too loose then go back in as needed. If you don't and you think the original set stud will be correct you will likely be wrong as any valve being new can stand higher-longer to be tight and throw you off. Why you loosen all of them way too loose and go back in one at a time.
 
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