I don't know much about engines...

[Maker]

But I took one apart anyway.

It's a 2.5HP Briggs and Stratton off a rotivator, it had been skipped (Probably for a good reason) so it cost me nothing, hence no great loss if I ruin it.

I got it all apart and cleaned it all easily but now I'm putting it back together I'm having trouble.

Firstly, I didn't mark the gears on the cam and crank shaft before I took them out so I don't know exactly where they meshed. There's a line scribed into one and a drill mark in the other which I assumed were the original timing marks so I put them back together with them aligned but I'm not sure that's right - The exhaust valve starts to open when the piston is about 1/8" from the bottom of it's stroke. Does that sound about right?

I was thinking that was wrong but it's just occurred to me as I type that the crankshaft can barely be a few degrees away from the bottom of the stroke so it's not like it would be wasting a significant amount of energy that would otherwise be used so it makes sense that it should be that way.
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The second problem is the intake valve doesn't fully close on the compression stroke, I can fit a 0.1mm feeler gauge under it. Would it be acceptable to grind a teenie bit off the top of the bit that connects the cam lobes to the valve stem (No idea what it's called, it looks like a 4mm pin with a 13mm circular head, all precision ground, hopefully you can tell what I mean from that).

Other than that it appear to be in very good condition. There's a bit of rust and it's caked in mud but nothing was seized or obviously worn.



I'll upload some pics tomorrow (Technically today now).

 

[graffian]

The exhaust will open sometime before bottom dead centre and the intake some time before top dead centre.
If you can see the cam at TDC the two lobes will be pointing away from it. The tappet will be on both base circles.
If those are the only timing marks and the lobes look right I would guess that's correct.
The bit your talking about is a cam follower/tappet, there should be adjutment for clearance.
Valve wants to be shut, look for tappet adjustment, shouldn't be any need to grind anything away, unless
your valves are sunk a lot.
so before you attack anything with a grinder check for an adjuster..

 

[carbon]

The way to adjust the clearance on the side valve engine is to remove the valve and grind a little of the valve stem rather than the cam follower/tappet as this youtube clip Side valve clearance

 

[Wendelspanswick]

The fact that the exhaust valves doesn't seat is most probably why it was scrapped as the engine would have no compression. It's perfectly acceptable to grind a small amount from the end of the valve if no other adjustment method is available, you should be able to Google the valve clearances.

 

[Ton-up]

What engine is it? Some of the Briggs dont close the valves fully so they are easy to start. Reduces the compression for electric starters.

 

[Pete.]

The way to adjust the clearance on the side valve engine is to remove the valve and grind a little of the valve stem rather than the cam follower/tappet as this youtube clip Side valve clearance

The vertical shaft mower engines are similar. I didn't bother stripping the engine down, I just removed the cover and use a thin flat file which I have ground a vee-point on the end to wedge in the gap until the valve opens against the spring and filed the clearance. Did my mower a few years ago and it's still running great.

 

[KemppiFrog]

What engine is it? Some of the Briggs dont close the valves fully so they are easy to start. Reduces the compression for electric starters.

Yes, quite common on Briggs & Scrapem. There is a gizmo on the camshaft that lifts the valve a bit, then as soon as it turns a bit faster (like firing) centrifugal force takes it out of the way, so the valve closes properly. Wether your 2.5 has one, I don't know.
KF

 

[Maker]

Yes, quite common on Briggs & Scrapem. There is a gizmo on the camshaft that lifts the valve a bit, then as soon as it turns a bit faster (like firing) centrifugal force takes it out of the way, so the valve closes properly. Wether your 2.5 has one, I don't know.
KF

The camshaft is solid, it's just a shaft with two lobes and a gear. I assume that means it does not have one and it needs some grinding.

 

[wristpin]

Stamped into the blower housing / cowling will be the words Model, Type, Code. Below each word will be some numbers which will identify the engine precisely; even to the year, month and day of manufacture. That information will assist in giving you precise information .
However all Briggs side valve clearances are checked with the piston quarter of an inch down the bore on the power stroke. Valve clearances on older BS side valve engines were 5-7 thou inlet and 7-11 thou exhaust Grinding the end of the valve stem is the way to achieve more clearance .
Do not grind the cam or cam follower/ tappet. Older, low horse power BS engines did not have any mechanical / centrifugal decompressor but achieved it by the cam profile.

 

[mechman]

Had the same problem with a Briggs 8bhp. Filed the exhaust valve stem to suit the makers setting and it started first go.