Jump to content

Valve Grinding & Lapping


Recommended Posts

Unless you are in "the trade", Doing a decoke & valve grind is not something, you do every week.  I can go several years between such exercises. However, at the weekend, I had need to carry out same. Not on a Corolla; but on my trusty Greenfield ride on mower, fitted with with a B&S V twin 22Hp air cooled engine. It did cross my my mind, however, that this engine, which I can lift with two hands, puts out over 50% of the HP, that my olde 4K engine does; an engine you need a chain block to lift. 

I have all the gear to do a valve grind, but as with anything, not used often; things like the rubber suction caps on the end of the lapping tools have gone a bit hard, & not as flexible as they used to be.  In addition to that, the end of the valve, where you "stick" the suction cap, can be a bit pitted, & the vacuum technique used to keep the valve & tool as one, doesn't work anymore.

So I could've headed for SCA to grab a new one, but came up with an idea, that worked brilliantly.

I always carry a couple of rolls of double side adhesive tape. There is one I have which comes from Bunnings, which is about 23mm in width, & very thick at about 2mm.

image.png.16cc663ff4481f7277f9ec68cc2e98f1.png

I cut a bit off, & suck it to the end of the valve. Trimmed it so that it didn't exceed the diameter of the valve; & then with the valve, in the head, pressed the lapping tool rubber cup, hard down on the exposed double sided tape.  Worked absolutely perfectly.

Only one problem, When I opened my little olde cylinder of valve grinding pastes (coarse & fine) I found they were both very dry & in lumps. Could've needed a trip to SCA, but I tried to revive the hardened lumps, & it worked perfectly.

Put a few lumps in an upturned lid of an jam jar, or similar.  Add a little bit of sewing machine "light" oil, (also referred to 3 In 1 oil),  to the hardened lumps, & at the same time, break up the lumps with a small screwdriver, or sharp object. 

image.png.5f0807b7a513fa066fcd6268d4987d71.png

Didn't quite get the job finished, as a big thunderstorm came, with threatening hail, & it was time to get the vehicles under cover.

image.png.ee849d0c4fb790a1eebcc472595bcc49.png

Oh well, there's always next weekend !

image.png.7883d93b12dee90c16a3a5c617064dfd.png

Cheers Banjo

 

 

Edited by Banjo
adding copy
Link to comment
Share on other sites

Members dont see this ad

Nice!

I hope you had a drill in the vice and put the valve stem in the chuck then spun the carbon off the back with some #80grit dry paper & followed up with #180 wet 'n dry and some WD40...   All that extra flow adds to the power you know!

I thought you'd be converting it to an outboard engine!

Link to comment
Share on other sites

The old man's old Briggs and Stratton would loose compression every so often.

Would pull the gear and smack the exhaust valve a few times to knock the carbon off it.

Worked everything.

Link to comment
Share on other sites

Posted (edited)
Quote

I hope you had a drill in the vice and put the valve stem in the chuck then spun the carbon off the back with some #80grit dry paper & followed up with #180 wet 'n dry and some WD40...   All that extra flow adds to the power you know!

Nope Keith !  But just as good.  I have two pieces of soft wood that I sandwich the valve stem in the bench vice, with the valve sticking out of the vice horizontally.  Then with the hand drill, & a brass drill circular wire brush, I clean both sides of the valve poppet head, cleaning all soot & carbon, without scratching the valve seat.  Works for me. 

 

Quote

The old man's old Briggs and Stratton would loose compression every so often.

 Col, you wouldn't believe what was the matter with this B & S engine. This is the very first time, I've ever done anything at all to the engine, besides oil & filter changes.

The previous run of the mower was about a 4 hour stint; as with all the rain in S.E. Qld., you can actually watch the grass grow.  I started the engine up a week later, & it was backfiring & lacked power. Felt like it was running on one cylinder.  Checked the plugs & they were very "sooty".  Cleaned them, but problem persisted. Suspected carby, with stuck needle & seat; but no; all good. Checked compression. Very low on one cylinder.   Removed rocker covers.  One cylinder has a bent pushrod, & the other pushrod had fallen out altogether, & was lying there; also bent. Serious, me thinks. What I couldn't get over intially; was that one push rod was steel, & one was aluminium.  Something strange, so off to Dr Google.  What I read in the next 30 mins, blew me away. When these air cooled engines get really hot, the aluminium head metal expands quicker than the steel valve guide. This results in the valve guide moving upwards, to the point where the spring cannot be fully compressed, & bends the push rod. B & S knew about this "design fault" & made one of the push rods (intake) aluminium, so it would be sacrifical, & prevent the whole engine destroying itself.   Still can't believe it.  All it needed to stop this from happening, was to put a very small shoulder on the outer, at the bottom of the valve guide; & machine a location for that shoulder/step, in the head.

image.png.cf02d8e84bbe16da58e4f56aaf02240e.png

Quote

I thought you'd be converting it to an outboard engine!

What ?  Like this one . . . .

https://www.youtube.com/watch?v=ZKEUBW7M3F8

Still shaking my head !

Cheers Banjo

  

Edited by Banjo
add picture
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
×
  • Create New...