leakdown analysis on a briggs.

[38racing]

I know I did things a bit out of order here. Friend feels that his briggs 28 series OHV is consuming oil. It's 94 and well used but my daughter's had same symptom a couple summers ago and after checking a couple things I pulled the head. I found early stage head gasket failure. I replaced it and the oil consumption ended. Given age of friend's I figure I might as well start with the head gasket. It appeared to be fine. I then measured bore and it wasn't even close to the reject . No scratches on the cylinder. Not a lot of carbon buildup either. So I removed the valves and cleaned the head. Valves and seats looked ok. I lapped valves and reassembled. Decide to do leakdown at this point but had an issue with my tester. I updated the thread in the tool section about that. Friend dropped by before the leakdown and I discussed what I found. Adding oil isn't a big deal for him but he was concerned of an engine problem . Turns out he is using synthetic oil but in 5w30. That maybe could account for some consumption in an older engine. So the plan is to use only straight 30 from now on. So after discussion I get back to leakdown. I have piston at 1/4 past TDC compression. Both valves at spec. Intake at .004. I haven't set up yet for a good hold of the flywheel but at 30 psi I get 42 % leakage and it's clearly coming out carb intake. I guess that I am re-pulling the head to check the intake valve.

[bgsengine]

I know I did things a bit out of order here. Friend feels that his briggs 28 series OHV is consuming oil. It's 94 and well used but my daughter's had same symptom a couple summers ago and after checking a couple things I pulled the head. I found early stage head gasket failure. I replaced it and the oil consumption ended. Given age of friend's I figure I might as well start with the head gasket. It appeared to be fine. I then measured bore and it wasn't even close to the reject . No scratches on the cylinder. Not a lot of carbon buildup either. So I removed the valves and cleaned the head. Valves and seats looked ok. I lapped valves and reassembled. Decide to do leakdown at this point but had an issue with my tester. I updated the thread in the tool section about that. Friend dropped by before the leakdown and I discussed what I found. Adding oil isn't a big deal for him but he was concerned of an engine problem . Turns out he is using synthetic oil but in 5w30. That maybe could account for some consumption in an older engine. So the plan is to use only straight 30 from now on. So after discussion I get back to leakdown. I have piston at 1/4 past TDC compression. Both valves at spec. Intake at .004. I haven't set up yet for a good hold of the flywheel but at 30 psi I get 42 % leakage and it's clearly coming out carb intake. I guess that I am re-pulling the head to check the intake valve.

make sure you run that test with the breather hose disconnected from carburetor so you don't get fooled by air coming from crankcase via breather. - If it is coming from breather tube, then it's obviously coming from crankcase, not carb..

[KE4AVB]

I agree you can get fooled by the breather leakage into the intake at the carburetor.

Also when using the low pressure leak down where you able cycle the cylinder remove the push rods that way can mid and lower cylinder for ovaling and tapering leakage.

As for the oil I have switch over to the Kawasaki 15W50 full synthetic for all engines using pressurize oil systems. It contains zinc to plate the worn areas; although, I prefer to use an oil with Moly additive for this purpose. When I switched my 300 mile pu engine over to the oil with moly I gained 20-30 of oil pressure as the Moly did it job.

[38racing]

Carb was off when I tested so i was feeling air out the head opening. I pulled head and tested leakage on the intake valve with brake cleaner and it seeped past. I lapped the valve again and it passed the brake cleaner test. I reinstalled the head. I had not read the comments here or I would have tested with rockers off but anyway I set the valves first and again had piston 1/4 past tdc . I had valve cover off so I knew valves were fully closed. I held the crank with a breaker bar on the engine pulley nut. I slowly increased psi on the tester and again I hear hissing but I look at the gauge and see it's much higher. Turns out to be only 10 leak. That's when I realized the hissing now is from the push rod galley and not the intake port this time. I'm thinking 10% at the rings is about as good as I'll ever see on any engine.

[KE4AVB]

38, the trick on leak down is when you are listening to the leakage is have the dipstick out too. Then if you hear leakage at the push rod galley, is it loud at the galley or the dipstick? Louder at the dipstick is leakage pass the rings but if louder at the galley then usually it is the head gasket or warped head.

And yes 10% is very good as there will always be leakage pass the ring gaps. Most Briggs service manual have that if under 40% you are good but of course 20% is a lot better and I shoot for that. Beside a little help keep the rings lubed. To me 40% is way too much and I usually find the ring end gaps pass spec indicating heavy wear of both the rings and the cylinder.

[38racing]

I'll try and remember dipstick for future reference. In my case it was a new head gasket.

[38racing]

Murphy was by today. Had the machine ready to go with new blades and started for testing. It previously had slight surge until warm. Now it had major surge but would come and go. I held governor lever steady and it ran fine. Let go and runs fine for awhile, then surge again. I did a governor static adjustment but shaft was already fully turned in the correct direction. I noticed that the fuel filter (white with pump) had a clamp type that I never use so I expect it's old filter. I pulled it and found crap in it. Replaced and running fine again.

[KE4AVB]

That like me not going with instincts about an axle on a Tuff Torq hydro. Got and the JD service manual for the Z920M. It said to change the axle seal use an appropriate hub puller so I order a four point hub puller. Guess what the SM is wrong. And I verified that I had to remove the transaxle and remove the axle assembly to replace the seal by contacting Tuff Torq.

Boy was I hoping the JD manual was right but my previous experience with another Tuff Torq was pointing to the 4 plus hour job. I was hoping the manual was right, it would had a 30 minute job. Oh well $200 (US) wasted on the tool and the time waiting for it. Basically the hub is cold welded to the axle by the 300 fl/lb axle nut torque.

When will I learn to follow my instincts? But I willing try new ideas that might save myself a lot of work. Two of the mounting bolts are a real pain to get out as they are only accessible by wrench and only turn a max 1/6 turn at a time. It is that or drop the whole rear assembly and the last one I did that took over 8 hours but those bolts were completely inaccessible on the Z925A and I had to install a new transaxle on that one.