Intake valve seized/won't open; no clearance after adjusting

[Paolo]

Hi all.

Long-time reader, first-time poster.

I decided to check the valves since the engine has started to sound a little clicky, and the bike's just reached 14,500km (it had 4000 on it when I bought it, and I don't know whether the valves were checked during the prior ownership). So, equipped with the service manual, I proceeded to strip everything and, finally, to check the intake. It was quite out of spec, so I adjusted accordingly.

Having done that, I tightened the nut and for some unknown reason the valve gap/clearance had been reduced to nothing when I rechecked (but the valve adjusting screw had not moved - i.e. I held it in place with a tool when tightening the lock nut). Scratching my head, I again wound the crankshaft & radiator fan to the TDC settings and there was no change: the rocker moves but there is no slack. Despite repeating the crankshaft & radiator process several times, there was still no gap. I even tried both loosening and tightening the adjusting screw and still no clearance.

Hoping with little optimism that starting the engine might break it loose/open it, I reinstalled the cylinder case, reconnected the battery, and fired up the engine. It wouldn't start.

Any assistance would be greatly appreciated.

[Lafree]

Hi, are you sure that you have it on the compression stroke on TdC,were both valve clearances slack, turn the engine 360 degrees and check again.

[easyrider]

Seems like you did everything right. Start over ..align the timing marks and then loosen the lock nut and set to the required spec. Close down lock nut while holding the stem. Recheck clearance.Make sure your have correctly aligned the timing marks.Hand turn the crank a few times and see if the clearances are the same.

[Paolo]

Hi Lafree & Easy Rider,

Thanks for your responses - really appreciate it.

I just had another go and no change.

As you can see from the images, while TDC is set, there's still no gap.

Any ideas?

[pcx man]

You have the valve adjuster adjusted as tight as it will go. Proper adjustment will have threads above the lock nut.

[Paolo]

Hi Pcxman,

Well spotted - thanks.

Yes, I didn't have it that way when the problem first appeared, but must've done that when frantically loosening and tightening to get clearance.

I think I've solved the problem. Although I've been aligning everything correctly, it turns out that the radiator fan setting doesn't sit naturally on the line (no matter how many times I wind it; it's only off by around a millimetre/.039 inch). Accordingly I jammed a screwdriver in to lock it right on the indicator, and now I can fit in a feeler gauge!

Will set it, re-attach battery and report back soon.

P.S. Does anyone have tips for accessing the exhaust valve? It was damn hard just getting the bottom right-hand side screw off the cylinder cover, let alone getting access to the valve to adjust!

[fish]

When adjusting valves on scooters , or a/c VW's, the FIRST thing I check before attempting any changes to the valve lash, is that I CAN feel some movement when grabbing the adjustment screw & nut!
If I feel no movement then I know I've NOT got things at TopDeadCenter. Spin, align things and try again.
It is quite possible, esp. considering your scooter has done only 10,000 miles, that you began your valve adjustment procedure on the wrong revolution. ie....you were not at TDC when you started. All your symptoms point to this, IMHO.
Fish
You should be able to do the straw in spark plug hole thing to double check thst you are on top dead center stroke.

[aguim]

On ANY 4-stroke cylinder, there are TWO top-dead-centers. One happens when the piston reaches
the end of the EXHAUST stroke, the other one when the piston reaches the end of the COMPRESSION
stroke. The valves MUST be adjusted at TDC-compression ONLY (when both rocker arms are resting
on the cam's base circle (NOT the cam lobes' opening ramps).

To find true TDC : look at the intake valve opening...then closing. As it stops going UP, piston is starting compression stroke. A straw-in-the-plug- hole will tell as it STOPS going UP that TDC -
compression has been reached good enough (an old trick ALWAYS true). Personally on my
Forza I don't even bother searching for timing marks...)

[Robbie]

Hi, are you sure that you have it on the compression stroke on TdC,were both valve clearances slack, turn the engine 360 degrees and check again.

What Lafree said.

Are you sure you are setting top dead centre on the compression stroke? You could be setting top dead centre on the exhaust stroke which is never going to work. Turn the crank through 360 degrees and try again.

Likely to be some valve overlap meaning the valves could both be meant to be open at top dead centre on the exhaust stroke.

Edit: Agium beat me by a minute

[aguim]

Robbie,

great minds are having a meeting, here. hahaha

[Paolo]

Thanks for the additional info and tips guys. Yes, the manual mentions the exhaust cycle and to do another 360 turn. I tried this several times to no avail; it was still slightly off.

Engine starts now but there's still a rattling sound, although not as bad as initially.

I'm now redoing the clearance but am having a problem with the lock nut (interestingly, the abovementioned fan alignment issue is now gone). In the image you can see how far it it is from the the rocker, and while I'm able to get it to about halfway by means of a 9mm wrench and pliers, I'm now encountering substantial resistance, to the point where tigthening any further sees the pliers slipping off the square head of the adjusting screw. I'm a little worried about applying more force because I don't want to strip the square head. I've visited several hardware stores and all I get is a blank stare when asking for a tappet wrench (the part recommended in the service manual states "US Only"; I'm in AU). I did, however, find a kit on ebay that seems to include one that is the right size (looks to be either a 3mm/.11 in. or 4mm/.15 square head?).

After taking the attached photo, I decided to remove the lock nut and apply liberal amounts of engine oil to both it and the adjusting screw shaft. It helped a little but still can't get it to where it needs to go.

Looks like I'll have to order the tool and wait for arrival. That is, unless anyone has any ideas?

Thanks again all - really helpful.

[aguim]

OVERTIGHTENED= STRETCHED OUT= SCREWED.
STOP BEFORE YOU DESTROY IT.

[Paolo]

Thanks for the warning. I'll leave it and take it to the local honda mechanic. So, you mean that the adjusting screw is overtightened? I can get the right clearance with feeler gauge - just can't get lock nut further down.

Not sure where I went wrong here. Did this on a friend's Chinese GY6 recently; it took 5 minutes. Oh well, a learning experience.

[aguim]

Paolo,

I also overtightened nuts/bolts as a noob, years ago. Ruined a spark plug thread on a friend's
50cc 2-stroke...and got my lesson for good haha

[Paolo]

You got that right, Aguim!

Ah well, put it all back together ready for the honda doctor

[Vancho]

Have to use 2 hands same time with tool in each af them.
If you make it first time- it is normal that you was not success at the first time. Just some more practice are required

[Paolo]

Hi Pancho,

Yes, I did the two hand thing etc. but I guess it was a bad-luck day. Hangover probably didn't help either ;-)

[Vancho]

Hi Pancho,

Yes, I did the two hand thing etc. but I guess it was a bad-luck day. Hangover probably didn't help either ;-)

Oh yea- shit happens) Just take it easy and try again

[homie]

You people are scary maybe go watch some YT video's