Question about 1987 Honda XR 250 R

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Setting valves when you set valves what stroke should it be on and where should the piston be

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TDC on intake stroke

Posted on Jul 01, 2009

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Valve timing on a 1908 single cylinder petrol car engine with maximum 1200 rpm 6 inch stroke and 4 7/8 bore. what would be the best settings for maximum torque.


way that then was when valve timing principles were being developed that are the same as today
with the piston on tdc exhaust stroke
the cam lobes will be in a position so that a bit of crank movement anticlockwise moves the exhaust a bit and a bit clockwise moves the inlet a bit
as you bring the piston up on exhaust stroke you will see the exhaust valve starting to close and when you see the inlet valve start to open ( at or very close to TDC) that is called valve rock and that is exact valve timing even today
if you have the cam shaft out and want to install it initially bring the piston to tdc and place the cam lobes so one of each would be resting on a valve end , the adjust the teeth mesh to achieve the rock setting as above
as for ignition timing it was set by the levers on the steering column ( or for stationary engine , a lever at the distributor )but ran best about 6-10 degrees btdc Compression ratio then would have been around 7 to 1 and leaded fuel with and a octane rating of 85
it was retarded for easy cranking and starting and when running was advanced to the recommended setting

Jul 24, 2016 | Motorcycles

3 Answers

I have a 21 hp Briggs and Stratton model #331877, what are the valve settings?


Intake 003 - .005
Exhaust .005 - .007

Adjusted with the piston 1/4" past TDC of compression stroke for each cylinder.

Apr 10, 2015 | Craftsman Garden

1 Answer

How to adjust travel


1 intake down
2 compress up
3 power stroke down
4 exhaust up




if you start with you start with the piston just a couple of degrees past TDC (top dead center) so that it has started its return down


now set the valves so they are closed:
if you have an adjustable valve clearance's then your clearances should be noticeable like 10 thousands ( you should be able to move the lifter ( rocker arm ) and it will be loose up and down


with the spark plug still out; so you can see the piston coming to TDC and passing it to come down


turn the flywheel and watch the strokes and the condition of the valves


1 just past tdc, the intake valve opens and the piston goes down for the intake stroke


2. jst as the piston comes around BDC the intake valve should close and return to tdc with all valves closed ( the compression stroke )


3 just past TDC the ignition will fire and the piston will return down with both valves closed( the power stroke)


4 just past BDC the exhaust valve opend , the piston travels up and completes the exgaust stroke.




and after completing the exhause stroke and arriving at tdc the intake valve opens and you start over again 1,2,3,4

Sep 12, 2012 | Cars & Trucks

1 Answer

1971 ducati 350 scrambler how do u set the timeing


Set the piston to TDC (top dead center) this is the higest point the piston will rise before moving on to the down stroke, either by lining up the marks on the crank rotor or a long screw driver (large handle so it wont fall in) down the plug hole and watch for the highest point lock or hold at this point. The cams should be fitted next on the 'compression' stroke meaing the all valves should be closed when the cams are seated (no valves being pressed by cams) generally at this point the cam lobs face away from the valves, next stroke down (ignition of fuel) valves should be closed with the exhaust cam moving round ready to rock on to the exhaust valve as the piston rises to the top again (4th stroke exhaust) as the exhaust valve lobe rocks off the intake cam lobe should be starting to rock on opening the intake valve on the down stroke of the pistion.
Trun the engine over by hand to make sure no valves are knocking the piston.
Should be as follows
1. all valve clearance free/rocking at ' TDC 1st 'down' stroke (ignition of fuel) valves closed exhaust moving round but not pressing valve ,
2. 2nd stroke 'up' exhaust valve rocking open and closing as piston tops with the intake ready to rock on as the exhaust closes and piston tops (exhaust),
3.3rd stroke 'down' (intake of fuel) as the piston moves down the intake valve should be opening.
4. 4th stroke 'up' compression of fuel all valves rocking closed as the piston rises for the compression stroke back to TDC all valves closed/rocking free.

Intake, compression , ignition and exhaust. (**** squeeze bang blow)

Feb 23, 2012 | 1972 Ducati 350 Scrambler

1 Answer

How do i set the timing on a yz450


Set the piston to TDC (top dead center) this is the higest point the piston will rise before moving on to the down stroke, either by lining up the marks on the crank rotor or a long screw driver (large handle so it wont fall in) down the plug hole and watch for the highest point lock or hold at this point. If cam sprocket has marks line them with the cylinder head surface (sometimes the sprocket bolts) parallel.
The cams should be fitted next on the 'compression' stroke meaing the all valves should be closed when the cams are seated (no valves being pressed by cams) generally at this point the cam lobs face away from the valves , next stroke down (ignition of fuel) valves should be closed with the exhaust cam moving round ready to rock on to the exhaust valve as the piston rises to the top again (4th stroke exhaust) as the exhaust valve lobe rocks off the intake cam lobe should be starting to rock on opening the intake valve on the down stroke of the pistion.
Trun the engine over by hand to make sure no valves are knocking the piston.
Should be as follows
1. all valve clearance free/rocking at ' TDC 1st 'down' stroke (ignition of fuel) valves closed exhaust moving round but not pressing valve ,
2. 2nd stroke 'up' exhaust valve rocking open and closing as piston tops with the intake ready to rock on as the exhaust closes and piston tops (exhaust),
3.3rd stroke 'down' (intake of fuel) as the piston moves down the intake valve should be opening.
4. 4th stroke 'up' compression of fuel all valves rocking closed as the piston rises for the compression stroke back to TDC all valves closed/rocking free.

Intake, compression , ignition and exhaust. (**** squeeze bang blow)

Feb 22, 2012 | Yamaha Motorcycles

1 Answer

I need to know the over head vave setting for the intake and exhaust on a 17.5hp Briggs & Stratton vertical shaft, single stroke lawn mower.


hi pauly46 here

set piston to tdc compression stroke then run it down the bore a 1/4 inch

set the tappetts to inlet the bottom valve ( alloy push rod ) to a tightish 0.004" and set the
ex valve the top one ( steel push rod ) to 0.005"

setting at 1/4 pst tdc eliminates decompressor from upsetting valve clearance seting


cheers pauly46

Mar 26, 2011 | Briggs & Stratton Garden

2 Answers

Belt snapped an i have changed the valves i need


Fit them to the crank shaft, that gives you the rough positions. Given you have changed the valves in order and properly sprung you can set the bottom pully to the top(12 0'clock) position, noting which piston is at the top of its stroke, or vary it slightly so its at stroke, Check your head against the block and turn the cam so the inlet valve for that chamber is open. do the same with the next piston in your firing sequence, turning the camshaft accordingly, to ensure the inlet valve opens fully. Fit the gasket and tighten the nuts down lightly, set up the timingmarks by eye,fit the belt and by turning the bottom pully you should find there is no resistance between the piston heads and the valve seats, thats why you don't tighten the head down as not to damage the valves if not firing in line. You should be ok though, tighten the head down slowly checking the pistons and valve contact is not an issue, turning the engine with the socket a full revolution with every turn of the bolts. Once fully tightned, before torquing, turn the engine FULLY to ensure there is NO piston/valve contact, then fit all ancillaries, set timing using a standard strobe and the distributer. Hope this helps, it should do, Regards Dave

Jul 17, 2009 | 2002 Renault Sportwagon

1 Answer

17 hp briggs hard to start and blows back through the breather


Hello rfrazierL

>>From your Description it Sounds like the Valves Require Adjusting.
>>The Following is a Basic File I made for Setting the Valve Clearances. Any Input is Appreciated.
>>**I Do Not Use the Setting Called for by the OEMs. I have Found that the Following Works Best.
>>Remove the Valve Cover (on the Dead Cylinder for Twin Cylinder Engines).
>>Check the Push Tubes and make Sure they are Not Bent.
>>Set the Cylinder you are Setting the Valves on to Top Dead Center on the Compression Stroke When Setting the Valve Clearance. Now Loosen the Valve Adjuster Lock and Using a Blade Style Feeler Gauge, Set the Intake Valve Clearance to .004in -.006in and the Exhaust to .006in - .008in. Loosen and Tighten the Rocker Arm and the Feeler Gauge is Placed Between the Rocker Arm and the Valve Top where the Rocker Arm Pushes on the Valve.
>>***BE SURE TO TIGHTEN THE ADJUSTER LOCK AFTER YOU HAVE THE PROPER VALVE CLEARANCE***
>>I have had Better Performance Out of the Mowers and Less Burnt Valves Using these Settings. Be Sure the Piston is at TDC on the Compression Stroke.**
>>If you Remove the Valve Cover and then Turn the Engine by Hand, you can Watch the Intake Valve Movement. When the Intake Valve Closes, the Piston will Just Starting the Compression/Power Stroke.
>>On Some Engines you can Us a Straightened Coat Hanger and Feel the Piston.
>>Be Careful and Don't Jam the Wire in the Cylinder. Usually the Piston will Push the Wire Out of the Spark Plug Hole with No Problems.

Respectfully

John

Apr 20, 2009 | Craftsman 42 in. Deck 19.5hp Lawn Tractor

1 Answer

Need to know how to time honda harmony tiller


well
heres your 4 strokes

1 intake down
2 compress up
3 power stroke down
4 exhaust up


if you start with you start with the piston just a couple of degrees past TDC (top dead center) so that it has started its return down

now set the valves so they are closed:
if you have an adjustable valve clearance's then your clearances should be noticeable like 10 thousands ( you should be able to move the lifter ( rocker arm ) and it will be loose up and down

with the spark plug still out; so you can see the piston coming to TDC and passing it to come down

turn the flywheel and watch the strokes and the condition of the valves

1 just past tdc, the intake valve opens and the piston goes down for the intake stroke

2. jst as the piston comes around BDC the intake valve should close and return to tdc with all valves closed ( the compression stroke )

3 just past TDC the ignition will fire and the piston will return down with both valves closed( the power stroke)

4 just past BDC the exhaust valve opend , the piston travels up and completes the exgaust stroke.


and after completing the exhause stroke and arriving at tdc the intake valve opens and you start over again 1,2,3,4

Apr 14, 2009 | Honda Garden

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