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B&S Intek 18.5hp ohv valve adjustment questions

9 years ago

31P777 SINGLE cylinder motor.
A few questions as I have seen many different "ways" to adjust my valves.
One way is to rotate crank until upper exhaust? valve is fully decompressed and adjust intake valve. Then compress lower intake? valve completely and adjust the exhaust valve.

THEN, I read to turn crank 1/4" past tdc on compression stroke (where neither valve is moving and both are fully closed) and adjust both intake (.004) and exhaust (.006) at the same time without turning the crank any more. This is because my motor has a compression relief valve on the cam.

Now for my questions:
Which is the INTAKE valve on my motor? (I am pretty sure it's the bottom but internet info has also said the top??)
Also read where the intake valve's pushrod is aluminum and exhaust is steel but mine is opposite??) what should each be?
Thank you!!

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Comments (9)

tomplum
9 years ago
The intake valve is the lower of the two, should have the aluminum push rod- set to .003". The exhaust to .005". Before making the adjustment, check the rocker studs at the head (bottom) w/ a 10 mm wrench and make sure they are tight. The adjustment is done cold, 1/4" either past TDC or 1/4" back before once TDC is reached. TDC is where the piston reaches the top once the intake valve closes.
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johnpalmer6940
Original Author
9 years ago
So the intake pushrod is aluminum? Weird. My intake pushrod is steel. Why did they make the 2 different metals?
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rcmoser
9 years ago
Need to follow the exhaust port path to know which Is intake and exhaust. If in fact the al. is on the exhaust side then somebody has tampered with it and put it together wrong. IMO same reason the make compression release, so they can make component parts cheaper. With compression release don't take no heavy duty starter system to crank if over. Light weight equate to Cheaper manufacturing costs and design IMO Intake don't get as hot or stress at exhaust so parts can be made cheaper IMO of course.
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walt2002
9 years ago
" 1/4" either past TDC or 1/4" back before once TDC is reached."

???

Note that when properly installed, ALL B&S Engine use an aluminum push rod on the valve which is utilized for Compression release. In the case of B&S V twin Vanguard engines, the aluminum push rod is on the EXHAUST valve.

18.5 Intek would be on the Intake.

I can send you a Service Manual for your engine IF you like, address below, put in propber format and remind me, engine model number and what you want. I am having commuter trouble so don't be surprised at delayed reply.

Walt Conner
wconner5 at frontier dot com
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johnpalmer6940
Original Author
9 years ago
I think I read somewhere that you should rotate the pushrods around each valve adjustment to avoid uneven wear-is this correct?
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walt2002
9 years ago
Switching the aluminum push rod end for end will prolong its' life IF the engine is one of the older ones which has a fibre guide that the push rod rides on. Newer design does not have this guide so no need there.

Walt Conner
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HU-751787887
4 years ago
I have a 18.5 briggs that is hard starting and back fires out the exhaust when trying to start. I took the valve cover off and the exhaust valve had a tone of lash in it but there was no cap like the intake valve is one needed on the exhaust side ? Any other suggestions on the hard starting and back firing would be greatly appreciated
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tomplum
4 years ago
last modified: 4 years ago
Yes. It has the same cap. Look for it. It is magnetic should you have a small magnet on a stick. Was the rocker loose on that side? Look closely at how far the valve guide protrudes from the head. Without the seal on the intake valve, they would protrude about the same. The valves too should be sticking out both the same, either with the rockers removed or where you set the valve lash at- 1/4" past TDC after the intake closes. If the head checks out and you get the valve train reassembled / lash set you should be good to go.
0
HU-751787887
4 years ago
Got further in it and it ended up being the exhaust valve seat was out and wasnt letting the valve close completely .. thanks for the help
0

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