Valve clearances and lunched motor

[ttmadness]

Has anyone ever lunched their motor from not doing valve clearance checks?

I am starting to think it's a bunch of baloney with checking valve clearances so often. Maybe it's something the manufacturers state in order to make money at dealerships and cover their backs if anything goes wrong and try to claim warranty, for example, over revving the engine and running poor oil that can cause top end damage.

Every time I have checked valve clearances they have all been within tolerances. I have had some real ''high km'' bikes too.

Another thing that adds to all this is people with ticking cam chains thinking they have bad valve clearances... you generally can never hear the difference in valve clearances!!!

My argument is that everyone keeps saying you need to check/adjust them or you will burn valves/blow your engine etc, but I have not read about the first instance of this happening. You would think that with all the undisciplined riders out there that someone would have had a engine blow that could have been avoided with scheduled maintenance.

[ttmadness]

Is it correct that if you were to actually have a case of a significantly out of spec valve clearance/clearances that your motor would be hard to start and have low power due to short valve lift duration?

Is it also correct that the most likely cause to ever damage your engine through unadjusted valves is tightening of the exhaust valves, causing excess heat?

[Brian d marge]

Japanese design thinking is for the engine to last a set km without major maintenance , the buying culture ( which is changing slightly ) tends towards selling at low ish km

the deals on a new bike is pretty good so there is no point in keeping one that needs such a check

The big 4 tend to have an inward looking design philosophy ( go china ! )

your 600 responds REALLY well to correct valve timing ( transforms them almost )

its not hard to check.

Stephen

[ttmadness]

what about modern bikes vs older 90s bikes?

[Brian d marge]

what about modern bikes vs older 90s bikes?
from memory is was about the 3rd version of the Cbr that had the jump in first service km , 24000 ?? so about the mid 90s around the fireblade coming out

I think what u are worried about is that by not sticking to the service schedule you will lunch the motor , all things being equal and with oil changes ,,, dont worry about it to much

on the bad side , Ive got it in the back of my head that once the valve tightens and lifts it runs away on itself

So a check is at least safe and sound


and on that note , the cost of a second hand engine , is almost the possibly even cheaper than a dealers valve check????

that might be worth a look into

Stephen

[AllanB]

On new Hondas they are around 24,000. That's a few years running for most riders so bloody cheap insurance having them checked for good motoring.

[Owl]

My first valve check at 17,000km had 2 within spec, 4 just out and 6 well out. All shims were replaced and set even. At 30,000km there was slight movement with the inlet clearances, but still well within spec.

The first check was noticeably quieter after adjustment.

[gammaguy]

Has anyone ever lunched their motor from not doing valve clearance checks?

I am starting to think it's a bunch of baloney with checking valve clearances so often. Maybe it's something the manufacturers state in order to make money at dealerships and cover their backs if anything goes wrong and try to claim warranty, for example, over revving the engine and running poor oil that can cause top end damage.

Every time I have checked valve clearances they have all been within tolerances. I have had some real ''high km'' bikes too.

Another thing that adds to all this is people with ticking cam chains thinking they have bad valve clearances... you generally can never hear the difference in valve clearances!!!

My argument is that everyone keeps saying you need to check/adjust them or you will burn valves/blow your engine etc, but I have not read about the first instance of this happening. You would think that with all the undisciplined riders out there that someone would have had a engine blow that could have been avoided with scheduled maintenance.


Its like a lot of motorcycles maintenance wise.

It s not what happens when you do it,its what happens when you dont.

I have seen huge damage caused by too tight valve clearances,which could have been prevented by a check when scheduled.

Unless you have X-Ray vision or super acute hearing(Hi superman)I would recommend doing them as recommended,at least until you get an idea of if and when they need adjusting,then you can modify the check schedule on that basis.

If I had a dollar for every engine I have rebuilt where the owner told me he thought the valves never needed checking,i would be a rich man:yes:

[tri boy]

Tight valves/no clearance means fucked components in the top end=$$$$$$$$
Now, ask yaself this,
Ya feeling lucky, Well are ya, punk.
(apologies to Dirty Harry)

[Mental Trousers]

If valve clearances tighten up the valves start hammering against the seats, bending things that shouldn't ever be bent. Tends to be the cause of most motors dropping a valve. Problem is it's impossible to diagnose after the motor has exploded.

[pete376403]

If valve clearances tighten up the valves start hammering against the seats, bending things that shouldn't ever be bent. Tends to be the cause of most motors dropping a valve. Problem is it's impossible to diagnose after the motor has exploded.

I've always understood that hammering seats, dropping valves is more a result of floating the valves from over-revving, with poor quality valve springs not being able to keep the cam follower accurately following the cam profile.

Tight (ie insufficient) exhaust clearance will eventually result in burnt valves as the valve head cannot transfer heat to the seat. Once the valve head is burnt the seat will probably go as well as there is a flame path across. Tight inlet valves are not such an issue, apart from the resultant lack of compression.
Valve clearances usually close up over time as the valve head sinks (wears) into the seat, more the case with old motors and unleaded

[Brian d marge]

Im stopping the gasoline causing the problems type of argument right here ... Never heard gasoline blamed for so much stuff until I spent some time in NZ :gob::facepalm: ( yes there was one batch from Singapore that melted some escort drivers oring ,,,,,

anyway You don't have to be anal about checking , ,,I mean think about it , a brand new bike fresh from the factory , doesn't need a valve check for 24k , and to be honest I would be surprised if they were out ... ( the unscrupulous dealer in me coming out now )

but what are the service intervals . 6000km with the valves every second one ??? ( off top of head ) . if you just flicked the gauge under them once a year , you might notice the middle exhaust ( Im doing this from memory so please forgive ) tightening slightly

Your call on how anal you want to be


Oil

its amazing how many Kilometers this new stuff can do ...........

Stephen

[Brian d marge]

If I had a dollar for every engine I have rebuilt where the owner told me he thought the valves never needed checking,i would be a rich man:yes:

Can beat that

Hondas larges warranty claim , Honda 50 , for ,,,,no oil ( didn't think it needed it )

Oh they are out there all right , they may be your neighbor

or at the movies ,,,with your sister :gob::gob::gob:

Stephen

heard that a long time ago so with a pinch of salt ,

[jonbuoy]

Has anyone ever lunched their motor from not doing valve clearance checks?

I am starting to think it's a bunch of baloney with checking valve clearances so often. Maybe it's something the manufacturers state in order to make money at dealerships and cover their backs if anything goes wrong and try to claim warranty, for example, over revving the engine and running poor oil that can cause top end damage.

Every time I have checked valve clearances they have all been within tolerances. I have had some real ''high km'' bikes too.

Another thing that adds to all this is people with ticking cam chains thinking they have bad valve clearances... you generally can never hear the difference in valve clearances!!!

My argument is that everyone keeps saying you need to check/adjust them or you will burn valves/blow your engine etc, but I have not read about the first instance of this happening. You would think that with all the undisciplined riders out there that someone would have had a engine blow that could have been avoided with scheduled maintenance.

This has to be a joke? I guess you don´t need to change the oil either - never looks that bad when I drain it :facepalm: You might not hear a tight clearance but you´ll burn out the valve if it can´t close when the big bang happens - the valve seat and cylinder head acts as a heat sink transferring heat away from the valve itself. A loose clearance you will hear less dangerous to your engine unless its real sloppy and slappy.

[Mental Trousers]

I've always understood that hammering seats, dropping valves is more a result of floating the valves from over-revving, with poor quality valve springs not being able to keep the cam follower accurately following the cam profile.

As I understand it, that happens a fair bit but usually only on motors that are a bit tired already or have been fiddled with.

Most bikes have their rev limit set comfortably below what they can actually do. For instance, from the factory mine is set to start reducing petrol @ 13,500rpm (it doesn't cut the ignition and is a much better way of doing things if you ask me) and completely cut it at 13,900rpm. Whereas these engines are perfectly capable of going until 14,500rpm before totally cutting the petrol delivery.

On modern bikes dropping a valve due to over-revving isn't such an issue because they already do lots of revs.

I could be wrong of course.

[Max Preload]

Valve clearances tend to tighten, not loosen, due to creep in the valve stem and seat recession so it's important to check them for being too tight because they'll burn valves much more readily with that situation. Cam wear doesn't come into that because the valve should never be touching the non-lift section of the cam on a conventional spring return valve - that's what the clearance is designed to avoid.

[Max Preload]

For instance, from the factory mine is set to start reducing petrol @ 13,500rpm (it doesn't cut the ignition and is a much better way of doing things if you ask me) and completely cut it at 13,900rpm.I doubt that very much because a lean mixture at those sort of revs for nearly any duration is fatal. Cylinder temperature rises rapidly.

It's much better to cut the ignition too, for mechanical reasons.

[Mental Trousers]

I doubt that very much because a lean mixture at those sort of revs for nearly any duration is fatal. Cylinder temperature rises rapidly.

It's much better to cut the ignition too, for mechanical reasons.

It runs lean for a very short period of time (like 10th's of a second) and quickly ends up too lean to fire at all but is still squirting some petrol in there, which then takes some heat away.

Cutting fuel gradually means it approaches the cut off point slower, ie it's losing impetus by the time it hits cut off. Cutting the ignition means it's still going hard up to the cut off point so it's easier to over-rev, ie momentum takes it well over the cut off point.

[Max Preload]

It runs lean for a very short period of time (like 10th's of a second) and quickly ends up too lean to fire at all but is still squirting some petrol in there, which then takes some heat away.I'd say, if anything, it's immediately cut to well below the minimum explosive limit if not completely stopped.

Cutting fuel gradually means it approaches the cut off point slower, ie it's losing impetus by the time it hits cut off. Cutting the ignition means it's still going hard up to the cut off point so it's easier to over-rev, ie momentum takes it well over the cut off point.Momentum isn't going to result in over revving. As soon as the ignition is cut, acceleration stops and indeed reverses due to drag. Newton's first law.

[Mental Trousers]

I'd say, if anything, it's immediately cut to well below the minimum explosive limit if not completely stopped.

From what I've seen the sampling period for engine revs could be improved quite a bit and the air/fuel maps are quite coarse so it's likely to do exactly that.

[Flip]

Shit there are a lot of experts here.

Check your valves because the valve clearances do change for 2 reasons, 1, valve seat recession which closes the tappet gap and 2, wear in the cam-follower-rocker etc which increases the tappet gap.

If the tappet gap closes too much the valves are held open and the valve burns out. If the tappet gap is too large it reduces the motors efficiency, makes noise and causes extra wear to the cam-follower-rocker mechanism.

There is not a motor maker that would back the mixture off at full revs-power, why because exhaust valves run red hot, if the mixture leaned there would be free oxygen in the combustion gasses and these would reduce the valves to their component metal oxides very quickly. What the ECU does is retard the ignition, which reduces the power very effectively and backs the revs down very quickly.

Just imagine what the oxygen sensor would see and do if the exhaust gasses suddenly went lean, it would dump a whole pile more fuel into the system to keep the combustion within safe limits.

[Owl]

There is not a motor maker that would back the mixture off at full revs-power, why because exhaust valves run red hot, if the mixture leaned there would be free oxygen in the combustion gasses and these would reduce the valves to their component metal oxides very quickly. What the ECU does is retard the ignition, which reduces the power very effectively and backs the revs down very quickly.

Well I'm certainly no expert:no:, but just curious.

My S3 is supposed to start cutting fuel at 9450rpm and ignition at 9700rpm. Redline is 10,000rpm, so is this not normal? I've never found the limit, so I can't say what the fuck happens.

[Brian d marge]

Im no expert either ,,, just been doing it for donkeys years and have lots of brightly colored paper ,,,

if people actually sat down and looked at what they do , rather than what they think they do , the difference might be interesting

Brakes , oils , tyres you be surprised how good they actually are..., and how little of the potential we use

Some countries do not have the purchasing power or spares , and you would be shocked and amazed ( I was ) at what the ie engine can take try kero for two stroke fuel...

and think about this ,,, IF the bike was bought for say 1500 ....you can buy a second hand engine for 600 dollars and all things being equal it probably quicker to change the engine ... ( thinking cbr here as them is what I know )

is it even worth doing major maintenance ???


Me ... I bought an enfield both old and new ,, They have/had a different design philosophy cheap labour cheap parts , increased wear parts in the engine ( the oil pump worm drive is almost a change with every filter ,,,joking but you get the point)

Stephen

[Max Preload]

What the ECU does is retard the ignition, which reduces the power very effectively and backs the revs down very quickly.Good point. Just as it does with detonation when detected by a signal from a knock sensor.

Just imagine what the oxygen sensor would see and do if the exhaust gasses suddenly went lean, it would dump a whole pile more fuel into the system to keep the combustion within safe limits.Well, that's down to the ECU and the fuel map. The O2 is only a feedback so may be ignored in that part of the map in favour of a default duty cycle on the injectors. I've never heard of it being done though except for cold start enrichment when the O2 sensor is useless.

[Mental Trousers]

All of the Triumph maps I've looked at (mostly factory maps for Daytonas and Speed Fours using TuneBoy) all reduce fuel until it's cut completely. It's a separate section for inputting when to start cutting and when to completely kill the fuel.

232979

[pzkpfw]

...and think about this ,,, IF the bike was bought for say 1500 ....you can buy a second hand engine for 600 dollars and all things being equal it probably quicker to change the engine ... ( thinking cbr here as them is what I know )...

So basically you are hoping the previous owner of the second hand engine did the maintenance that was required?


(Having said that, my bike is getting lower and lower in value, so it's hardly worth selling to "upgrade". So I'm almost considering buying one like it as a "spare". The idea would be an engine out could easily have stuff like valve clearances done, in leasure, on a nice bench. Then an engine swap when ready.

Just dreaming, really. I'm far too cheap/lazy to do that...)

[Brian d marge]

So basically you are hoping the previous owner of the second hand engine did the maintenance that was required?

(Having said that, my bike is getting lower and lower in value, so it's hardly worth selling to "upgrade". So I'm almost considering buying one like it as a "spare". The idea would be an engine out could easily have stuff like valve clearances done, in leasure, on a nice bench. Then an engine swap when ready.

Just dreaming, really. I'm far too cheap/lazy to do that...)

well its that ole how long is a bit of string thing really , assume average use ...500 for cash

hoping it aint knicked

Stephen

its frames I need for my bike , have 3 engines ,,,one frame:sick:

[george formby]

Interestin.

It seems most of this thread is about fours. How important are regular checks on a 5 valve parallel twin & er, how difficult is it?

[pete376403]

About half as busy as a 5 valve inline four. I did the clearances on an FZR1000 with the cylinder head on the workbench. It was straightforward, but fiddly (the shims are tiny, about 6mm diameter) Pays to be methodical if you dont want to be taking the cams out more than once.
I don't think I'd like to do it with the motor in the frame.

OTOH old Suzuki fours are a piece of piss. With the right tools you don't even have to take the cams out.

[george formby]

About half as busy as a 5 valve inline four. I did the clearances on an FZR1000 with the cylinder head on the workbench. It was straightforward, but fiddly (the shims are tiny, about 6mm diameter) Pays to be methodical if you dont want to be taking the cams out more than once.
I don't think I'd like to do it with the motor in the frame.

OTOH old Suzuki fours are a piece of piss. With the right tools you don't even have to take the cams out.

Thank you. I will start saving up then.:yes: I'm a mechanical numpty & the last time I looked at a shim it belonged to a CB 750 integra, about the size of a $1.50 coin.

[gammaguy]

what a lot of people dont know is that valve clearances are also impoortant for cooling,mainly in the exhaust valves.

The length of time the valve spends on its seat(dictated by the clearance)also dictates how much heat will be dissipated from the head of the valve and therefore cooled.

Not enough time on the seat and its hello burned valves:eek:

[Pussy]

You can get slightly better low end and mid-range power when the valve lash is set at the looser side of spec, too