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MG · 05-07-2012, 11:11 AM

Topic Approved

**princesirohi** · 05-07-2012, 03:43 PM

if both the valves are shut, petrol will not enter the combustion chamber, so it will not start, but if there is some left over petrol vapours in it, it will ignite and probably there will be some damage to piston rings or valves.

**ashwinprakas** · 05-09-2012, 09:50 AM

Originally posted by princesirohi View Post

if both the valves are shut, petrol will not enter the combustion chamber, so it will not start, but if there is some left over petrol vapours in it, it will ignite and probably there will be some damage to piston rings or valves.

I doubt anything will happen to the rings, I query is that th valves are shut but the engine is turned by the starter motor and hence I suspect either a misalignment of the timing chain with respect to its stock position on the timing wheel, causing the decompressor on cam to not work properly, OR since the valves are strained shut, either damaging the valves as youve described or wearing out the camshaft.

The problem here is technically all the above could happen, but as we all know experience matters as well, hence looking for advice from someone who has made the same mistake/experiment as myself.

**jd666** · 05-09-2012, 10:44 AM

I believe bikes above a certain capacity have an auto decompress, so this wont really happen.

Tappet adjusters are in push rod engines, on a over head cam there is a timing chain to run the cam. The adjustment is done thru shims between the valves and the cam actuator.

And if the auto decompress does not happen/is not present, the piston will ideally back down the same way, not going the full cycle.

**ROCKRZ** · 05-09-2012, 11:22 AM

Originally posted by ashwinprakas View Post

Guys I want you're expert advice regarded to the behavior of valves in 4T's.

I want to know what the possible outcome of the below given scenereo is.

Bike cranked with started button when both the valves are forced shut by the tappet adjuster nut.

Bike in question : Hero Honda Karizma (ZMA)

afaik, the valves are only forced open by tappet adjustment screw. the nut merely holds the screw in position.

Maybe i am misunderstanding your question. I will upload a pic in evening to clarify which nut i am talking about

**princesirohi** · 05-09-2012, 11:25 AM

one more thing, i don't think you can force shut the valves by tightening the tappets, as tappet adjusters are just to maintain proper clearance, even if you over tighten it it won't shut both the valves as rocker arms control the valves and if you push the starter button overhead camshaft will move causing the rocker arms to move which will open valves.
to try your experiment you have to disconnect valves from cam-shaft by removing rocker arms , then only you can permanently close the valves.

but why do you wanna try this?

**jd666** · 05-09-2012, 11:26 AM

^^ you are right. you will have to remove the cam to force the valves shut

:facepalm:

**psr** · 05-09-2012, 12:50 PM

Force opening with wrong valve clearance setting is possible, not force closing.....
Both valves will remain closed during compression, and explosion cycle,so there is no issue in the valves remaining closed and engine cranked.Please understand the four stroke cycle .....

engine animation - 4-stroke start & run

http://www.youtube.com/watch?v=2Yx32F1cncg

line drawing animation of a four stroke engine starting an running. My first attempt. Little surprise at the end

**ashwinprakas** · 05-09-2012, 06:04 PM

Thanks everyone ive learnt alot from your posts and so that means that the valves can not be forced shut, so what's will happen if the adjuster screws a tightened at their maximum tightest position and lockd in place whith the lock nut and engine is cranked using the starter.

From a laymans point of view here are the things that happened,
1. When done by myself the engine just cranked but didn't fire up.

2. When done by Arun bro, the engine cranked when the starter was passed, but bike didn't start and there was a white smoke which had the smell of petrol coming from the air filter (I may have failed to notices the same cause I'm having a stock intake where as Arun bro is having a free flow intake.)

Can you please explain the reason for the above outcomes, and the possibility of any damage that might have happened to the engine,while the same was done.

**psr** · 05-09-2012, 08:53 PM

Originally posted by ashwinprakas View Post

2. When done by Arun bro, the engine cranked when the starter was passed, but bike didn't start and there was a white smoke which had the smell of petrol coming from the air filter (I may have failed to notices the same cause I'm having a stock intake where as Arun bro is having a free flow intake.)

Can you please explain the reason for the above outcomes, and the possibility of any damage that might have happened to the engine,while the same was done.

When the adjuster is tightened beyond the settings recommended then there is a chance of valves remaining open , even at TDC leading to gas escape through exhaust and ignition gas expansion through inlet called back firing through inlet....again see the animation and learn..

**jd666** · 05-09-2012, 09:02 PM

To be honest this was a very " First let me find out what everyone else knows and then Ill answer my findings " type of question.

Possibly the engine was at different points in the combustion cycle, thats when you cranked and someone else cranked it.

**ashwinprakas** · 05-09-2012, 10:58 PM

Originally posted by psr View Post

When the adjuster is tightened beyond the settings recommended then there is a chance of valves remaining open , even at TDC leading to gas escape through exhaust and ignition gas expansion through inlet called back firing through inlet....again see the animation and learn..

Thanks sir, now all my queries are settled, in short theres no permanent damage caused by doing the same other than loss of AFR as you explained. I just wanted to be 100% certain whether we could rule out this possibility which in turn we were suspecting is causing the kicker to behave wired in our bikes.

Originally posted by jd666 View Post

To be honest this was a very " First let me find out what everyone else knows and then Ill answer my findings " type of question.

Possibly the engine was at different points in the combustion cycle, thats when you cranked and someone else cranked it.

Sorry for the awkward question just wanted to clear things out, cause me and another xbhpian have been facing kicker issues with our bikes, so was ruling out by making a list of all the stupid things we did with the bike which were common in both our cases. Since this is ruled out, the next query is whether cranking the starter when the kicker is in engaged position will cause it to behave strangely.

For those wondering what's wrong with my kicker heres a video.

2011 ZMA Kickstart - YouTube

**srpsinu** · 05-10-2012, 12:33 AM

I couldnt get you....perhaps you are trying to say that you have increased valve clearance to the point that the valves no longer open even when the rockers are at the top of cam lobe...in that case the engine wont start because fresh charge is not being admitted into engine(intake valve always closed). Pl make your query clearer.

**princesirohi** · 05-10-2012, 01:41 AM

Originally posted by psr View Post

Force opening with wrong valve clearance setting is possible, not force closing.....
Both valves will remain closed during compression, and explosion cycle,so there is no issue in the valves remaining closed and engine cranked.Please understand the four stroke cycle .....

ofcourse both the valves will remain closed during two cycles compression and combustion, what he meant was if valves are permenantly closed for all cycles.

Originally posted by jd666 View Post

To be honest this was a very " First let me find out what everyone else knows and then Ill answer my findings " type of question.
.

yes, absolutely. 100%

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Expert advice needed related to valves.

Expert advice needed related to valves.

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