I assure you I have the claimed 12:1, I have cced everything and done the calculations. Even if I had room more decking would only raise compression ratio, large valve overlap and valve timing events affect the cranking compression.
Plug fouling and idle issues
- Thread starter wkong
- Start date
I assure you I have the claimed 12:1, I have cced everything and done the calculations. Even if I had room more decking would only raise compression ratio, large valve overlap and valve timing events affect the cranking compression.
wkong
CB750 Member
I guess I should add that I already adjusted the valves to manual specs... have I put the motor in danger if I don’t know how far they may have gone with this supposed 836?
wkong
CB750 Member
Stock is .002/.003, while all of cycle x performance cams list .004 across the board... that’s a pretty big difference. Craaaap.
Aftermarket cams are all over the place as far as clearance spec. My RC Eng 327 cam uses .012 on both. Most of the megacycle cams use .005. The lobe profile and the lash go hand in hand in managing and keeping the valve train undercontrol and for longevity. So yes if the cam is designed for a wide clearance and you tighten it up you can cause damage to the valve train. Lobe design and the lash are use to "gently" open the valve...if such an event can be gentle. The lash helps to cushion the opening of the valve. It is difficult to know what you got unless you take it apart...you could maybe take a dial indicator through the tappet hole and try and get an accurate lift measurement thencould determine if it is stock lift or if it is higher lift.
wkong
CB750 Member
Got it, thanks for the reply. Would I be able to drop a borescope in a tappet cover to get a visual on the cam? Would seeing it even help identify it or do I need to be able to take measurements on it?
Alternatively, I could lift the top cover enough to see what’s inside using a camera without removing the engine, but if the gasket gets buggered I’ve gotta pull the engine anyway. I’ve got 4 weekends to get this thing out of my garage and I’ve still got plenty of other odds and ends..
Another idea. If tight valves drop compression, I could check them at stock settings, then set them all to .004 and see what the difference is?
About the only thing you might be able to see would be if the cam lobes had been welded up, but you kinda gotta know what to look for, some are really hard to tell. Most aftermarket cams are marked on the very end of the cam, sometimes under the bolt and washer on the one end.
You wont notice a measurable compression difference by changing valve clearance.
You wont notice a measurable compression difference by changing valve clearance.
wkong
CB750 Member
The borescope I’ve got takes pretty good quality pics... or I leave it as is, give it to my buddy and tell him he might have a valve/cam/rocker job in his future.
I suppose if I can get it to idle well set to stock clearances I probably am fine.
I suppose if I can get it to idle well set to stock clearances I probably am fine.
wkong
CB750 Member
I’ve been working on this thing for four months pretty non stopped and I think build exhaustion hit me for a second. At the very least I’ll try using a dial indicator to measure the lift. Do you have the stock numbers? I see .315 intake and .313 exhaust.
amc49
CB750 Guru
.001" or .002" is not going to kill you setting the valves unless it's toward the tight side. The cam makers loosen up trying to get the cams to get some oil on the lobes so they last longer.
Its not all just about getting oil in there.
That is pretty close to the stock cam lift minus the rocker ratio. Its probably stock. If your measurement is accurate then it looks like the lobes may have a slight amount of wear but it is easy to throw the reading off if you are not 100% straight above the valve. You will be ok with stock clearances by the looks of it.
wkong
CB750 Member
Looking at the likely suspects as far as popular cams in a run of the mill 836, at manual settings I could be .003 and .002 off. Maybe .002 and .001 off. The lift on some of these cams appears to be as much as .03 higher than the stock numbers I found, which would be real easy to see... let’s hope I’m good with a dial indicator this weekend.
amc49
CB750 Guru
'Its not all just about getting oil in there.'
A change of 1 or 2 thou in valve clearance is not going to hurt the clearance ramps or lash take up, the base circle allows for that.
Increasing the valve clearance certainly does not help the clearance ramps or lash take up as it takes up space they would normally want to use. Yet the parts have to get lube. I myself assume your big number of .012" given above has nothing to do with clearance ramps or lash take up, rather the stout valvesprings needed with that cam likely shove parts around in extra deflection and warpage and the extra space is needed to make sure the valves stay closed. It could be because of a turbo cam use as well and the need to make sure the exhaust valve still closes with the additional length increase it will grow from the extra heat.
A change of 1 or 2 thou in valve clearance is not going to hurt the clearance ramps or lash take up, the base circle allows for that.
Increasing the valve clearance certainly does not help the clearance ramps or lash take up as it takes up space they would normally want to use. Yet the parts have to get lube. I myself assume your big number of .012" given above has nothing to do with clearance ramps or lash take up, rather the stout valvesprings needed with that cam likely shove parts around in extra deflection and warpage and the extra space is needed to make sure the valves stay closed. It could be because of a turbo cam use as well and the need to make sure the exhaust valve still closes with the additional length increase it will grow from the extra heat.
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Not a turbo cam, not even CLOSE. Anyway its a moot point arguing with you as it will get the OP nowhere and you know everything anyway.
wkong
CB750 Member
Ah, sorry, I meant I was seeing those numbers as stock online, haven’t checked mine yet
Yes that is pretty close. The actual numbers changed as they went on in production even though they didnt publish the change and actually used the same part number even though the specs changed. Was done to satisfy emissions. Thank you EPA.
Getting back on subject with your bike, I am still somewhat suspect as to the lower voltage at the coils, it should be battery voltage to the coils. Any drop indicates resistance and could be causing low spark output. You had two plugs that are white which indicates lean...air leak or fuel restriction. Honestly I would pull carbs and recheck jets for restrictions, visually check bench sync(all should be close, I use a very small drill bit as a guide and set all 4 to same opening set to thickness of drill bit. Still resync after running) Put float level back to stock, I have never had an issue where I needed to deviate from stock, even with aftermarket floats. Double check everything in carb including the needle clip positions, its probably right but at this point in the troubleshooting I would recheck everything. Recheck compression, reset all valves to stock unless we determine you have a different cam. Check your ignition advancer...make sure it moves free. Set timing to stock, you did adjust both pickups on the electonic ignition right? Start over and look into the voltage drop you have to the coils. Also what ignition system and coils are you using?
wkong
CB750 Member
Thanks a lot for all that. I was able to adjust things to get 12.3 at the coil posts with 12.8 at the battery. Drops to 11.8 with the lights on.
I pulled the carbs and the jets are clear, they’re bench synced. I realized I set the floats while the carbs were flat so they’re all set too high when just touching the valve spring. I also have cheap rebuild kit valves in, so I ordered genuine ones and will set it to 26mm just touching the spring tip. All needles are in the middle clip, sticking out of the main jet hole the same amount.
I checked compression on 1&4 and got 135 and 140. The last time I checked compression on 2&3 the adapter started to cross thread and then so did the plugs, I got 2 in okay but had to use a back tap to clear the first thread in the head on 3, so I really really don’t want to get back in that situation by checking them again. They were both in that 127-135 range when I did check them.
Valves are set to stock specs.
Advancer operates correctly, it’s a dyna s and I did set both 1&4 and 2&3 to between the advance marks at 2500 rpms.
Coils are 5 ohm magna.
amc49
CB750 Guru
I will leave you cats alone to deal with the issue, as I apparently talk too much.
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Thanks and yes you do.
