16HP Vanguard valve adjustment

[Gumby83]

I’ve been fighting a B&S vanguard engine (303447-1188-E1) for far too long. It’s installed in a ball field drag, if that matters - all it does is operate 2 hydraulic pumps via belts - the pumps operate all the attachments and drive system on the ball drag.

What started as an oil change and spark plug replacement has turned into a daily migraine. Plugs were replaced because #2 cylinder was dead and both plugs were severely worn. Cylinder was still dead with the new plug. I checked for spark on both coils and there was no spark at all from #2 - tried adjusting air gap to .008” - still nothing. So I put new coils on it (I’d have to look back at the paperwork - I know they weren’t genuine Briggs coils but I don’t know where my boss found them), air gap set to .010” and then was getting spark from both coils.

Since then, it’s been very picky about starting, and when I finally tried cranking with the air filter off to observe the fuel spray into the Venturi, it was backfiring through the carburetor.

I pulled the covers and inspected the pushrods - they weren’t bent. I adjusted the valves - engine cold (sat overnight) I set the pistons to 1/4” past TDC compression stroke using a dial indicator - adjusted rockers to .005” clearance - and that’s where the frustration really starts. Despite my best efforts, I can’t get the rockers to hold the adjustment while tightening the adjustment nut. Every time I set it, it will inevitably tighten down to less than .005” even though I’m holding the adjuster screw.

Are there any tricks/suggestions for maintaining the clearance adjustment while tightening the nut?

 

[tom3]

Not too uncommon for this. The lock nut takes up the slack in the threads on the adjuster, a real small amount will show up at the valve tip. Just adjust a couple thousands loose to get the right clearance when all secured. Might rotate the flywheel back and forth while checking the clearance to make sure the cam was on base.

 

[Rivets]

I set the clearance slightly larger so when I do the final tightening they end up where I want them. + or - .001” will work fine.

 

[Hammermechanicman]

If you still have it put the working original coil back on and disconnect plug wire from the other cylinder with new coil and see if it backfires in the carb and is still hard to start.

 

[Gumby83]

Thanks Tom3 and Rivets. I’d been considering applying a couple drops of yellow thread lock to the adjustment screws and then giving it time to cure before reinserting them into the rockers. I figured that would create enough drag to hold the screw if nothing else. First I’ll try adjusting to .006” and see what I get.

If you still have it put the working original coil back on and disconnect plug wire from the other cylinder with new coil and see if it backfires in the carb and is still hard to start.

Thanks for the suggestion but The original coils are long gone. This ball drag has been in the shop for more than a year now because I’m only working on it as I have time (1-2 hours per month). Since I was getting adequate spark with the new coils I didn’t see the point in keeping the originals. I must admit, however, that I’m not sure what it would suggest from a diagnosis standpoint if I did as you’re describing.

Also can anyone explain why the piston has to be 1/4” past TDC? I haven’t actually measured the valve lift, but visually watching it and holding my hand against the rocker, there doesn’t seem to be any difference in valve lift between TDC and 1/4” past TDC.

 

[Rivets]

1/4” past TDC makes sure your settings are not affected by the compression release.

 

[Hammermechanicman]

Thanks Tom3 and Rivets. I’d been considering applying a couple drops of yellow thread lock to the adjustment screws and then giving it time to cure before reinserting them into the rockers. I figured that would create enough drag to hold the screw if nothing else. First I’ll try adjusting to .006” and see what I get.



Thanks for the suggestion but The original coils are long gone. This ball drag has been in the shop for more than a year now because I’m only working on it as I have time (1-2 hours per month). Since I was getting adequate spark with the new coils I didn’t see the point in keeping the originals. I must admit, however, that I’m not sure what it would suggest from a diagnosis standpoint if I did as you’re describing.

Also can anyone explain why the piston has to be 1/4” past TDC? I haven’t actually measured the valve lift, but visually watching it and holding my hand against the rocker, there doesn’t seem to be any difference in valve lift between TDC and 1/4” past TDC.

The reason i suggested putting in the original coil was because you said you got the non OEM coils form another person. Are you sure they are the correct coils? Did the engine run decent on one cylinder before you put the new coils on? From your first post it sounded like the problem started when you changed plugs and coils.

 

[Gumby83]

Thanks again Rivets - my experience with valve adjustment is primarily automotive so I’m used to adjusting them at TDC - I didn’t consider the compression release, so that makes sense. It was easy to find the adjustment procedure online but I didn’t find an explanation as to why.

The reason i suggested putting in the original coil was because you said you got the non OEM coils form another person. Are you sure they are the correct coils? Did the engine run decent on one cylinder before you put the new coils on? From your first post it sounded like the problem started when you changed plugs and coils.

Thanks again - this is why I appreciate forums like this one, because they help provide outside perspective on these things. It was so easy for me to ignore the coils as being responsible because they’re both providing good spark, but that doesn’t necessarily mean they are correct. I remember finding the part number on Brigg’s website, so I’ll make my boss find the receipt and verify if they’re supposed to be the right ones.

It occurred to me also that I could still kind of follow your advice with the new coils. Since the #2 cylinder was originally the dead one, I could just hook the coil to my spark tester so it’s grounded and see if the engine will run on #1 - then vice versa depending on the results.

Also, if anyone was curious, I have checked the compression on a couple different occasions and both cylinders had about 125 PSI (engine cold) so other than adjusting the valve clearance, I don’t suspect (at this point) this is a base mechanical issue, but we’ll see what the valve adjustment and coil tests show first.

 

[bertsmobile1]

Check that the fuel shut off solenoid is working then remove the kill wires from both coils and do a test mow.
The Hall Effect trigger modules can interfear with each other causing bad timing ,
Originally there was a diode in the loom to prevent this then they changed the chip in coils for twins to prevent this happening.
The mounting centres for twins is the same as that for the singles that do not need the modified chip and mowers have come in with 2 brand new cheap single cylinder coils that ran like a hairy goat much as you are describing

 

[Gumby83]

Ok, so it turns out that I was wrong about the coils - the ones we installed are the right ones according to the part number I found (591459).

We’re located in what’s becoming a suburb of Des Moines thanks to all the housing that’s being built lately, but most mower and small engine parts aren’t available for direct delivery to us, so when we need model specific parts, we either have to order them online or drive to Des Moines to get them. My boss found his receipt from the supplier and it showed they were Briggs coils matching the part number.

That said, I did get the valve clearances adjusted correctly by starting with .006” so thanks for that. I also attempted grounding one coil through my spark tester and trying to start with 1 active coil - it didn’t start with either cylinder.

Now, who knows their spark plugs? The plugs I originally installed - Champion RN14YC - were supplied by the customer, so I didn’t give them a second thought until today after I verified the coils were right. After crossing the Briggs part number to our [auto parts] supplier, it came back as RC14YC. I didn’t see any obvious differences between them except the size of the hex - 13/16 vs 5/8. Otherwise the heat range and electrode material were the same - but the actual resistance of the plug wasn’t stated. So, I ordered them just to compare the resistance, and if there’s a significant difference, I’ll install them and see what happens.

Check that the fuel shut off solenoid is working then remove the kill wires from both coils and do a test mow.
The Hall Effect trigger modules can interfear with each other causing bad timing ,
Originally there was a diode in the loom to prevent this then they changed the chip in coils for twins to prevent this happening.
The mounting centres for twins is the same as that for the singles that do not need the modified chip and mowers have come in with 2 brand new cheap single cylinder coils that ran like a hairy goat much as you are describing

Thanks for the input. I’ve already verified the fuel shutoff solenoid is functional, and the kill wire for the coils has been unhooked since I started on this thing. I had to chase a few wires when I first started messing with this thing because I’d never heard of the vanguard engines before. I’d have to look again but I don’t think this has a control module - only a regulator/rectifier for the charging voltage.

There is a single kill wire connecting the coils together under the cover, but the connection from the cover to the kill circuit is disconnected (grounds through the ignition switch, maybe? It’s been quite a while since I’ve looked at the diagram or physically traced the wire). Should I remove the wire connecting the coils?