Briggs Twin Thumping

[lefty]

407777-3195-G5 Code: 130413YG

This came to me for service. The owner mentioned the smell of burning oil when warm. I could tell that both valve covers were leaking. The bolts were looser than they should have been. So I replaced those and torqued to spec. When I was in there, I noticed that the valve lash on the number 2 exhaust was too tight. Just a couple of thou. So I checked, set the vavles to .005, which I found in the service manual.

Also, while I was in there, I did a leak down just to make sure there wasn't a blown head gasket contributing to the oil escaping. With 100psi in, I was holding 94-95 on both cylinders. But the number 2 had a tiny bit of air escaping from the intake. I have not addressed that yet.

When running, after it gets warm, I'm hearing some random popping from what seems to me to be the exhaust. I called it thumping because it's not really a loud popping. It's a lower tone. Kind of like what you would hear from an old tecumseh snow blower engine. I thought maybe the leaking intake may be the culprit but what's throwing me is the fact that it's only happening after warming up. Which makes me think it's valve lash. I also thought maybe worn cam lobes but again, I thought that would effect it immediately.

I guess my question would be, should I go a little prouder on the valve lash? I seem to remember someone suggesting a little wider on the exhaust but I can't remember who it was or for which engine. Also, how does compression release work on this? I see a good bump on the number 1 intake valve. I see a less defined bump on the number 2. But I would imagine that would only affect starting.

Thank you.

[lefty]

Well, I sorted this one out.

I spoke to the owner to see if he noticed any popping before he dropped it off. He told me he mows with headphones, listens to music, and doesn't hear anything. I took the valve covers off again thinking that maybe the number 2 exhaust valve fell out of spec again. I knew all the other valves were in spec when I checked them. I found that now the number 1 exhaust valve jam nut and adjustment screw assembly were sitting at the bottom of the galley. The rocker and rod were just flopping around. Fortunately, there was no damage to the rod. So I went ahead and reinstalled it. I decided to go 5 in. lbs proud on all the valve jam nut torques to make sure they hold. This is the one where the center 40 torx is the adjustment and the 13mm nut is the jam.

Is this common on the v twin? I know valves falling out of spec is common on the other style of adjustment jam nut setups. Does anyone go with any Loctite on these? I've used Loctite on rocker studs in the past but never on the adjustment setup.

Thanks.

[38racing]

Well, I sorted this one out.

I spoke to the owner to see if he noticed any popping before he dropped it off. He told me he mows with headphones, listens to music, and doesn't hear anything. I took the valve covers off again thinking that maybe the number 2 exhaust valve fell out of spec again. I knew all the other valves were in spec when I checked them. I found that now the number 1 exhaust valve jam nut and adjustment screw assembly were sitting at the bottom of the galley. The rocker and rod were just flopping around. Fortunately, there was no damage to the rod. So I went ahead and reinstalled it. I decided to go 5 in. lbs proud on all the valve jam nut torques to make sure they hold. This is the one where the center 40 torx is the adjustment and the 13mm nut is the jam.

Is this common on the v twin? I know valves falling out of spec is common on the other style of adjustment jam nut setups. Does anyone go with any Loctite on these? I've used Loctite on rocker studs in the past but never on the adjustment setup.

Thanks.

5 inch pounds? It's 45 I think on the single cylinder briggs 28 and 31 series

[lefty]

I found 60 in the twin manual I have.

[bgsengine]

5 inch pounds? It's 45 I think on the single cylinder briggs 28 and 31 series

Umm yeah .,. have to re-read his post - he did say "5 inch pounds PROUD" meaning if spec was 45 in-lb, he'd be going to 50 in-lb, etc...

[38racing]

5 inch pounds? It's 45 I think on the single cylinder briggs 28 and 31 series

Umm yeah .,. have to re-read his post - he did say "5 inch pounds PROUD" meaning if spec was 45 in-lb, he'd be going to 50 in-lb, etc...

I just realized his setup on twin is different than single. Single had the 20 torx in centre of adjusting nut.
I was working on a rato engine. Flywheel nut torque spec was 52 NM or 38 ft lbs. I was watching a YouTube and fellow was do flywheel on a gcv160 and said torque was 50 ft lbs. Luckily he didn't put rope in cylinder to hold it and when he couldn't hold it he dropped the torque wrench and just bumped a bit with impact. I once mistakenly thought it was 50 ft lbs for a tecumseh 5 hp snowblower engine. I broke off the endof the crankshaft

[Arkie]

I've considered trying blue or green locktite but would have to completely remove and clean all really good for the locktite to do any locking due to the oil soaked pieces.

Another reason I considered locktite is to help get maybe a more user friendly adjustment due to the setting changing as the jam nut was torqued. (some are lots of trial and error for me when getting the intake lash at minimum specs)
But I've never had them come loose as you described but I made sure they are jammed tight.

I suspect the compression release is on the grind of the cam on the intake valve lift on the Briggs OHV twin Inteks, because when I see them hard to crank due to compression I take the Intake lash to minimum and get a good crank usually.
Maybe someone will chime in about the Twin Intek compression release to answer (our) your question???????????????

[jerkputter123]

I looked up the camshaft for this model engine. I didn't see a ACR on the camshaft.
Part number for the cam is 797242 according the numbers that were posted.
You can view it here and judge for yourself.
https://www.ebay.com/itm/166342404450?_ ... 1506.m1851

[bgsengine]

I looked up the camshaft for this model engine. I didn't see a ACR on the camshaft.
Part number for the cam is 797242 according the numbers that were posted.
You can view it here and judge for yourself.

Briggs cam ACRs, many of them are machined into the cam lobes, so you won't see a mechanical release... means they will have an ACR bump that will be there at all RPMs...