Valve clearances

[MikeL]

My CB-1 has now done 55,000 km and since buying it at 25,000 I have done nothing to the engine. I have no idea whether the valve clearances were checked before I bought it (I suspect not). It runs well and I'm reluctant to either pay what I think will be a fairly sizeable amount of money to have the job done (it's a bucket and shim thingy) or try to do it myself, which with my mechanical ineptitude would probably be a recipe for disaster. I mainly use the bike for commuting so reliability and economics are more important considerations than performance. It's hard for me to judge whether over the couple of years I've been running it anything has changed in terms of power, acceleration etc. (especially since I bought the XJR), but it might be that performance has gradually dropped off a little bit, and perhaps the engine sounds a tad more "tizzy" than it used to.
So what do you reckon? Leave well enough alone? What is the worst-case scenario?

[Two Smoker]

i got the Valve clearance done on my ZXR... HUGE DIFFERNECE!!! Far better throttle response, as well as greatly inproved power and torque throughout the rev range...

[Motu]

With the hardened valve seats and general improvment in quality valve, adjustments are a thing of the past in the car world,we just don't do it anymore,I expect bikes are the same.

10 yrs or so ago I was brought a TT250 motor,totaly abused...maintenance was so bad that it threw a shagged chain and smashed the cases - it was my job to fit some secondhand cases.But pulling it down I found the head was also cracked,so got another later model cyl head,minus valves and cams.I lapped the original valves into the replacement head,assembled it and did my first valve clearance check - I was totaly amazed to find all 4 valves at exactly the right gap! Manufacturing tolerances are so precise these days that 2 cyl heads 5 yrs apart in build date were exactly the same.That was a Yamaha mind you - I doubt if Honda can match the quality....

[John]

All I will say is when my valves were done (after supossedly never being done) my bike goes NUTS, no other way to explain it - also helped my fuel consumption conciderable (they were REAL bad).

[Posh Tourer :P]

it might be that performance has gradually dropped off a little bit, and perhaps the engine sounds a tad more "tizzy" than it used to.
So what do you reckon? Leave well enough alone? What is the worst-case scenario?

You might have a touch less power as the valves open a bit late, but does it matter? If the engine starts to really rattle, maybe have a look, but it probably isnt worth the bother if it isnt clattering. Worst case scenario for loose valves is loss of power. Tizzy is good, as no noise could mean too tight and valves hitting pistons due to not closing properly.....

[Blackbird]

Hi Mike

I suspect that your motor is very similar in setup to the Blackbird. From memory, the recommended valve clearance checks are at 25000 km intervals. They have a reputation for not moving. It's extremely rare that they need adjusting but at 55000 km, I'd be inclined to get them done for peace of mind - the plugs too if you haven't changed them. I've done 40000 km on the 'bird and have never had them done, but will have a full service as soon as I get back from the Southern Cross. Cost will be just over $500 for the full service. Oh, and I don't think that rattling is a guide as I'm pretty sure that the clearances close up, not open due to shim extrusion and valve head thinning on these motors. Might be wrong, but I'm sure I read that on the 'bird website ages ago. If that's the case, a burnt valve is a (remote) possibility if the clearances are out.

Cheers

Geoff

[FROSTY:Me]

dude I wouldn't be worried about loose valves--itd be making a hell of a racket Its tight valves that may be an issue. As mentioned before if thge valves tight it could cause them to get burnt --then its a big expense.

[Motu]

For those who get a performance increase after setting valves - is that all that was done? Nothing else? If they were so far out you can feel a difference I'd be thinking of flicking the turd off onto someone else....

Tappets noisy when loose and quiet when tight? Not always.....most production cams in the last 50 yrs have quietning ramps,so the clearance is taken up slowly before the serious lifting takes place,but if clearances are loose or tight then the ramp is working incorrectly and you can have noise.Back when I rode Triumph twins we knew when our tappets were tight because they became noisy.Cam timing checks are done with 20 thou gaps,this takes out the ramps - not just Triumphs,it's almost universal,find any specs on cam timing and you'll find they specify 20 thou....or um,some metric thing I can't think in for valve clearances.

I know with the modern 4 stroke dirt bikes to get the same weight and performance as a 2 stroke they have pared down the valves so much that tuliping of the heads is just a matter of time....about 5000km street use,but in off road use valves may need repacing after a season,or maybe after each race in competion - sports bikes don't have such a high level of performance,so don't need valves replacing.

[MikeL]

Hmm... some conflicting opinions here...

I've got a big service on the XJR coming up shortly so the Honda will have to wait a while, but it seems from what I read here that there is at least a theoretical possiblity of some serious damage.

The workshop manual specifies valve clearance checks at 25,000 kms and details the work. It looks way beyond my competence. I particularly appreciate the warning not to drop bits into the crankcase...

[Blackbird]

It's a job I'm going to leave to the professionals because I'd rather use the limited spare time I have doing something more enjoyable. Besides, not having done it before, there's a good chance of me cocking it up! On the 'bird, you have to dismantle half the bike to get to the engine and I can't be bothered with the hassle.

Your use of the word "theoretical" is apt. A slight risk but not likely. Depends how much peace of mind you want. I'm going to get mine done and then forget about it for another 40000 km!

Cheers

Geoff

[Zapf]

Hmm... some conflicting opinions here...

I've got a big service on the XJR coming up shortly so the Honda will have to wait a while, but it seems from what I read here that there is at least a theoretical possiblity of some serious damage.

The workshop manual specifies valve clearance checks at 25,000 kms and details the work. It looks way beyond my competence. I particularly appreciate the warning not to drop bits into the crankcase...

what year is your CB1/400 ? just wondering..

[MikeL]

what year is your CB1/400 ? just wondering..

It's a 1989 model, Jap import

[Posh Tourer :P]

Tappets noisy when loose and quiet when tight? Not always.....most production cams in the last 50 yrs have quietning ramps,so the clearance is taken up slowly before the serious lifting takes place,but if clearances are loose or tight then the ramp is working incorrectly and you can have noise.

What happened to good old rocker arms?? They are all so much less confusing....

[Kwaka-Kid]

no touchy touchy of the valvulators!!

... Suspect i just mated 1x valve with 1x piston bound to = big metal mess ... we shall see in engine takedown

[craisin]

of course if the valves ran cooler you get less wear. eg oilcooler or upgraded oilcooler and or additives. Read about building top drag V8s in the states with multi-stage oilpumps that scavange oil from where there is an excess pump it thru a cooler and spray it onto the valvesprings= cooler valves