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Valve Adjustment..

#1

Michael72

Michael72

Hi Folks

Just to ask your thoughts on briggs valve adjustment....I see so many vids today where OHV'S and flat heads are adjusted at TDC and not turned over so the piston is down 1/4" as specified by Briggs....

To add... on a 3.5 classic im working on at the moment the piston will travel slightly above cylinder block so to measure from top of block will give you more than 1/4"... either way the feeler gauge is giving the same reading from valve stem to rod weather I turn down 1/4 or not!... i dunno :)


#2

Carscw

Carscw

Best way to adjust valves.

Turn the flywheel counterclockwise 2 times.
Stop when one valve is open adjust the closed valve. Repeat for the other valve.

Sent from my iPhone using LMF


#3

Michael72

Michael72

Hi

Thanks.... makes sense to do it that way...proper reading etc :thumbsup:


#4

pugaltitude

pugaltitude

Michael72 said:
Hi Folks

Just to ask your thoughts on briggs valve adjustment....I see so many vids today where OHV'S and flat heads are adjusted at TDC and not turned over so the piston is down 1/4" as specified by Briggs....

To add... on a 3.5 classic im working on at the moment the piston will travel slightly above cylinder block so to measure from top of block will give you more than 1/4"... either way the feeler gauge is giving the same reading from valve stem to rod weather I turn down 1/4 or not!... i dunno :)
Click to expand...

I think you are being a bit to precise when checking valves on this engine.

Usually a screw driver down the plug hole and turn past TDC on the power stroke and measure approx. 1/4" or 10mmish.

The reason for doing this is because if it is before TDC then the decomp on the cam shaft is in the wrong position and may open the valve slightly which would give you a wrong reading.

Also I cant remember the last time I set valves on a classic due to them being so reliable.


#5

Michael72

Michael72

Hi

Thanks for the reply...I had the head off anyway as compression was down so I suspected valve seating issues...yes being to fussy :) good advise ...thank you


#6

M

motoman

CAUTION , DO NOT READ IF ALLERGIC TO TRIVIA :laughing::cool:

Mike, Some blather which might explain what you observe measuring the same in different (small) rotations of the engine aroung TDC. A "mild" cam lobe grind has a very "pointed" lift shape so the bottom portion of the cam lobe is a symmetrical circle. When you note an unchanged clearance with a feeler gauge you are reading this unchanged contour. If you ever see a "radical" cam grind pictured it has "ramps" that start much sooner to slam open the valve instead of gently lift it. On such a cam you would see the clearance area around that same area greatly reduced.. If you are interested in "messing" around while you still have the head off you can determine a precise TDC mark by using something bolted to head wich stops the piston from reaching TDC. Rotate the piston one way until the piston is stopped and mark; remove the stop and go past, rebolt and rotate the other way and mark. Remove. Half way between the two marks is TDC. I put a small center punch mark with red ink on my Intek. This is overkill for such slow running engines. I do not know why the factory did not put on such a mark, but perhaps it is with the same marketing philosopy which publishes the Intek owners manual without a required valve adjustment , but then includes unadjusted valves as a problem in the troubleshooting secion.


#7

S

SeniorCitizen

Michael72 said:
Hi

Thanks for the reply...I had the head off anyway as compression was down so I suspected valve seating issues...yes being to fussy :) good advise ...thank you
Click to expand...
Have the valves ever been lapped?


#8

Michael72

Michael72

Thanks all for the info...much appreciated... not my first rodeo with this but always good to have other opinions and advise....learn something new everyday until I forget it all the day after :smile:...the valves needed attention (some lapping) so compression issues solved....slight pitting but mainly some carbon build up...thanks again..:thumbsup:


#9

Michael72

Michael72

motoman said:
CAUTION , DO NOT READ IF ALLERGIC TO TRIVIA :laughing::cool:

Mike, Some blather which might explain what you observe measuring the same in different (small) rotations of the engine aroung TDC. A "mild" cam lobe grind has a very "pointed" lift shape so the bottom portion of the cam lobe is a symmetrical circle. When you note an unchanged clearance with a feeler gauge you are reading this unchanged contour. If you ever see a "radical" cam grind pictured it has "ramps" that start much sooner to slam open the valve instead of gently lift it. On such a cam you would see the clearance area around that same area greatly reduced.. If you are interested in "messing" around while you still have the head off you can determine a precise TDC mark by using something bolted to head wich stops the piston from reaching TDC. Rotate the piston one way until the piston is stopped and mark; remove the stop and go past, rebolt and rotate the other way and mark. Remove. Half way between the two marks is TDC. I put a small center punch mark with red ink on my Intek. This is overkill for such slow running engines. I do not know why the factory did not put on such a mark, but perhaps it is with the same marketing philosopy which publishes the Intek owners manual without a required valve adjustment , but then includes unadjusted valves as a problem in the troubleshooting secion.
Click to expand...

I can do trivia lol....good read and thanks


#10

R

Rivets

Why don't owners manual include valve clearance? CYA by the manufacturers, because 95% of owners would cause more damage or injuries if they attempted to adjusted the valves. I would say that 90% of the techs out there, under the age of 30, don't know how the adjust or lap valves on an L-head engine.


#11

Michael72

Michael72

true... I do enjoy getting these old solid blocks in to work on....getting few and far between nowadays unfortunately....


#12

M

motoman

My point on the absence of owner manual callout for valve attention on (my) Intek is that it is short sighted , not that any owner should attempt such maintenance himself. So Craftsman is doing an upside down favor to the owner. Read the troublshooting guide first to understand that valves may need attention. At sale point in Sears in 2004 there was verbal counseling to find a service tech. Is this just another "I've got a secret" example buried in marketing taboo? And, of course, my familiar rant about overheating...blah, blah,blah. :thumbsup:


#13

B

bertsmobile1

Michael72 said:
I can do trivia lol....good read and thanks
Click to expand...

Go see Professor Google using piston drop vs crank rotation calculator as your question.
When you find a calculator plug in some numbers and you will see when you get close to TDC ( or BDC ) you get a massive amount of rotation for a very tiny amount of piston drop.
That is why the piston stop method mentioned earlier is the only method worth using for Joe Public.
I have used the valve fully open while adjusting the other for all my life as I was brought up with BSA motorcycles that use substantial opening & closing ramps.

Also take in the comment that you are working on a lawnmower in a very soft ( thus forgiving ) state of tune and not a NASCAR top fueler.

I get mowers in all the time with either no valve clearence at all ( no I never let it run out of all what makes ou ask that ) or clearances that are 2 to 3 times bigger than std.
Most of them are running when they come in they are just had to start ( takes 1/2 can of starter fluid ) or arn't quite running right ( doing 4000 rpm or unable to exeed 2000 ).

Sprit series are really low tech, low tune & thus very tollerant to low / no maintenance


#14

Michael72

Michael72

bertsmobile1 said:
Go see Professor Google using piston drop vs crank rotation calculator as your question.
When you find a calculator plug in some numbers and you will see when you get close to TDC ( or BDC ) you get a massive amount of rotation for a very tiny amount of piston drop.
That is why the piston stop method mentioned earlier is the only method worth using for Joe Public.
I have used the valve fully open while adjusting the other for all my life as I was brought up with BSA motorcycles that use substantial opening & closing ramps.

Also take in the comment that you are working on a lawnmower in a very soft ( thus forgiving ) state of tune and not a NASCAR top fueler.

I get mowers in all the time with either no valve clearence at all ( no I never let it run out of all what makes ou ask that ) or clearances that are 2 to 3 times bigger than std.
Most of them are running when they come in they are just had to start ( takes 1/2 can of starter fluid ) or arn't quite running right ( doing 4000 rpm or unable to exeed 2000 ).

Sprit series are really low tech, low tune & thus very tollerant to low / no maintenance
Click to expand...



Bingo thank you :)...Ok... its just a 35 classic, piece of cake...The aim of the thread was to pull some info from the big boys at the other side of the pond :) ...having had bikes myself for years and some work on an Yamaha XT 500 of late that is the method I used and use to correct valves ( one open,...) IMO it is the only way to find the true relation of valve stem to rod, when the valves are actually working so to speak (Not possible for every motor I know)....Not to many of us small engine folk round these parts so its good to hear other opinions/experience etc... :thumbsup:


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