B&S 28Q777 crankcase vacuum line sucking oil up to fuel pump

[warreng5995]

You indicated that you checked the oil after doing a leak down. This may sound like a dumb question but did you clean the dipstick and then check it? Or just pull the stick and check it? Some air always gets by the piston during leak-down and pressurizing the crankcase will force oil up the stick.

Most on here are wiser than I am but if you have fuel in the oil and are losing air through the intake, you have two problems. The intake valve and leaking carb, I would think. Did the oil smell like fuel? 8 oz is enough to make a stink I would imagine.

yep, checked oil level when engine cold and it was at full mark. Checked again when it was hot, it was over full. But then checked it again later after engine cold, and it was back down to the full mark. And yes I always clean the dipstick off first
I looked at the oil and smelled of it, but no it didn't smell like gas which surprised me seeing it was showing over full at the time. But like I said, it went back down the full mark after the engine cooled, so I don't know. never seen this happen before. the only guess i have is because of the intake valve leaking, it could be causing the engine to overheat and make the oil 'expand'... or cause air to get trapped somewhere making it look like the oil level had risen??? idk

 

[Megalosdog]

Hey all, first time poster.
My Dad has a Dixon 4515B ZTR mower that he got from his nephew... yeah its about 20 years old, I believe it to be a 2000 model
It has a Vanguard 15.5hp OHV engine #28Q777-0691-E1 (photo attached)

It all started... thats how most projects begin right ... with repairing the mower deck where it was rusting out only in the front section, and I welded in new sheet metal and etc etc...

In any case, engine had an oil leak that had kept slowly getting worse, so wanted to get that fixed too. Appeared to be dipstick tube seal. Went to replace it, and when doing so I began cleaning all the old oil off the mower frame etc. Began to see oil going up the side of the block up under the engine cover, realized it must be the crankshaft seal under flywheel. Went to replace that, while doing so had the carb and air intake off. Happened to look into the intake side of the head and saw it was thickly coated in baked on oil . Long story short, ended up removing engine, complete tear down, found a thick layer of baked on oil (carbon buildup) all inside of head, top of piston, valves covered (not even sure if they were closing fully) etc. Oil in bottom of case was about a 1/2" of thick gel like sludge.The apparent problem was the bottom piston ring was stuck bad with a good amount of carbon build up, oil ring was stuck but came lose fairly easily when I began to mess with it.Top ring was moved ok, but there was build up in the groove. Seemed obvious that oil had been blowing by up into head.

After getting everything completely disassembled and several days worth of cleaning until all parts were spotless... all internal parts looked good. No scoring on cylinder sleeve nor piston, crank and cam had no scoring and no real wear, all teeth were sharp and square (not worn). Cam pressure release looked and operated just fine. Governor gearing was perfect, no wear, operated fine. etc etc .Got full engine gasket and seal kit, ring set, full carb rebuild kit including new float and float bowl (after cleaning found a tiny pin hole in old bowl). Rebuilt entire engine, including deglazing cylinder sleeve, lapping valves, as well as checking head and block for "flatness" using a slab of granite I keep in the shop. Used engine assembly lube on crank, cam, rod connector, pin, etc etc etc. Torqed everything to B&S specs as listed in their service manual, including the head in correct 3 rounds of increasing torque to final spec, and in correct order.

Reinstalled engine onto mower, and finished up installing carb, starter ect. Filled with conventional 10w30 oil and new B&S filter.
Took mower out for a short run, seemed to run good but not the power that it should have had. When engaging electric clutch for mower deck, engine bogged down significantly before coming back up to speed. When cutting any grass that was thick at all or "taller" than the rest, could hear the engine bog. At first thought maybe governor tab might needed adjusting (carb doesn't really have any adjustments but one) etc. Brought mower in and parked it as I didn't have the time that day.

Fast forward to two days ago, my Dad took mower out cut for about 20 min (just to test as grass isn't tall just beginning to grow), I could hear the mower bogging some as before etc. UPS truck shows up at our gate, my Dad drives down shuts mower off. UPS leaves, mower cranks but will not restart, doesn't even try to hit. I was in the shop, heard it, walked down to see what the problem was. Couldn't see any reason, thought maybe it either wasn't getting fuel or it was flooded. Tried some starter fluid in the air intake, nothing... must be flooded. Towed it back up to the shop. Started to pull plug when I noticed some fluid in the vacuum line going from crankcase breather to the fuel pump (I use the 1/4" silicone transparent fuel lines on anything I replace now days due to issues I've had with the old style lines, which is why I could see the fluid in the line). Took line off fuel pump, poured it out into my hand and it appears to be a mix of oil and gas. Ok... fuel pump membrane must have a hole in it. Checked oil, level was good and no indication of the presence of gas. Bought new fuel pump and air filter (even though the one on it was fairly new). Ran again... more fluid in vacuum line, but this time it was only oil.

Spoke again with Kevin who owns my local Stihl dealer, I buy most of my small engines parts, saws, etc from him as they are good people to work with and knowledgeable.The only other thing he (and myself) could think of is if the crank case breather spring was broke or something blocking it etc. Replaced crankcase breather with new. Ran again for a few min, line clear. Seemed like it fixed that issue, but engine still didn't have the power it should.

Today decided to recheck valve clearances, they were a bit off, and I will say they sure are touchy... finally was satisfied I had the clearances correct. Took mower out, power was much improved... but still bogged some. Wanted to run it longer, get engine up to full temp etc. Mowed about 20 min or so. Brought back into shop, oil was back in the vacuum line yet again, and engine would not restart.

I'm out of ideas... just doesn't make sense to me. If I hadn't just replaced the head gasket and etc, I would say a blown head gasket was possibly the issues. And that it was pushing a bit of pressure into crankcase. which in turn was pushing the oil through the breather. But I just did the headgasket with everything else with all brand new B&S parts.

Any input would be much appreciated

Edit: Just thought I would note that Italics button works, but "Bold" text doesn't appear to be working on here for some reason...

Make sure that air filter is halfway clean. If the engine can't pull in fresh air through the filter, it'll suck it up through the crankcase breather hose. I've seen this a few times. Just a suggestion.

 

[warreng5995]

Make sure that air filter is halfway clean. If the engine can't pull in fresh air through the filter, it'll suck it up through the crankcase breather hose. I've seen this a few times. Just a suggestion.

Yep, already got a new filter and pre filter foam screen

 

[Born2Mow]

EDIT: Just wanted to add, as I stated in previous posts, I lapped the valves during the rebuild and they appeared to have seated well all the way around. BUT could the valve be bent just slightly enough to cause this?? Or maybe I just thought I had them seated good. Been a while since I lapped valves on a car engine.

Some ideas...

• You can't lap the valves and get 100% contact on the valve and the seat if the valve is bent. You could have the adjuster on the intake valve too tight, or your valve timing can be off, thus forcing the valve to leak.
• You stated you ran this test at TDC. But you did not state which TDC. There are 720 deg of crankshaft rotation in one full cycle of a 4-stroke engine. Novices often forget that with 2 full turns, the piston comes to TDC twice in that 720 deg, but the valves can only be adjusted at every other TDC. At one TDC both rockers should be tight (both valves slightly open). At the next TDC both valves are fully closed (both rockers loose). It's only this last TDC when you can adjust the valve clearance and do pressure testing.

Hope this helps.

 

[warreng5995]

Some ideas...

• You can't lap the valves and get 100% contact on the valve and the seat if the valve is bent. You could have the adjuster on the intake valve too tight, or your valve timing can be off, thus forcing the valve to leak.
• You stated you ran this test at TDC. But you did not state which TDC. There are 720 deg of crankshaft rotation in one full cycle of a 4-stroke engine. Novices often forget that with 2 full turns, the piston comes to TDC twice in that 720 deg, but the valves can only be adjusted at every other TDC. At one TDC both rockers should be tight (both valves slightly open). At the next TDC both valves are fully closed (both rockers loose). It's only this last TDC when you can adjust the valve clearance and do pressure testing.

Hope this helps.

Good points. As far as the valve being adjusted to tight, I know I did have a time with getting them set, at least to my satisfaction. With that said, both valve rocker arms were loose before I began to adjusting them.
If the valve was bent, I certainly couldn't tell it after I inspected them or when lapping. But I was just trying to think of any reasons that the intake valve would be leaking. And I had my crank and cam timing marks lined up when I reassembled the engine.

 

[warreng5995]

Alright... Here's the "update"...

today I removed the valve cover, then removed the rocker arms and rods. This eliminates it being the valves being adjusted wrong (which they still might have been off a bit), then after doing this I performed another leak down test. 100psi in, once again about 80 to 85 psi held in cylinder. Which again means 15 to 20% loss. But this time, there wasn't any air coming out the intake ... but I could still hear it blowing out somewhere, and after reaching in I could feel the air with my fingers at the head gasket between the cylinder and valve passage. I did retorque all the head bolts, which is at the 250 in lbs that StarTech said it had been updated to in the newer manuals. And tested it again, but it Made Zero Difference.

Kept looking, tried to see if I could find air coming out somewhere else etc. As I just couldn't figure why the headgasket would be bad, as its brand new. Finally I gave up, removing everything to get down to the head, and pulled the head. I expected to find... Something... Anything that would explain the pressure loss.
But Instead all I found was a thin film of oil in the bottom of the cylinder. Everything else, including the head gasket, looked perfect. I even took the head itself and sit it in a vice and did a "liquid leak" test on the valves with some WD-40, but it never leaked a bit. Letting it sit overnight just for the heck of it. Still not sure why air was leaking the other day through the air intake, unless I still didn't have the valves set right...

In anycase, I used a machined straight edge (which is about 1/2" wide) that is rated to be flat to .001 (1 thousandth), and I laid it across the section of the head between the cylinder and push rod area. The thinnest feeler gauge I have is a .0015 and it wouldn't even try to slide under. I also used a bright light behind the straight edge while I looked from the other side, and couldn't see any light underneath of it. Any sort of deviance THAT small should certainly be taken up by the headgasket!


So I don't know guys, its leaking out from a brand new head gasket without any obvious reason...When I work on anything... even building/fabricating, repair work, cars, tractors, whatever... I always try to do everything "the right way"... but I'm about to the point I'm going to do it the "country way". I am just about ready to get some JB Weld and coat each side the gasket, and slap this stupid thing back together and let it setup for a day or two. And if that doesn't "fix" it... I'm going to sell it for parts or whatever I can get out of it. I've already wasted FAR to much time and $ this past winter on this dixon, and my patients is just about out, as the weather has already broken and I've got other work that I've got to get to. Just need to get a cow and let it eat the grass... save me the time of cutting it...

 

[SHB]

I have seen others write about getting bad head gaskets, which leak latterly. You might try a new gasket and check for leaks?

 

[warreng5995]

I have seen others write about getting bad head gaskets, which leak latterly. You might try a new gasket and check for leaks?

its looks perfect... but you're right it still may just be a bad gasket. I'll take your advice and try another gasket, one last time.

 

[warreng5995]

QUESTION: I know on a car, you should never be able to spin/turn the valves in the head by hand. But what about in a briggs engine? with the valves installed in the head, I can apply a little pressure with my fingers to the "face" of the valve and turn it. is this normal for a mower engine? Or does this mean the springs are weak??

 

[warreng5995]

ok... after disassembly i re-lapped the valves again... just to make sure. then cleaning everything down with brake and carb cleaner. I reinstalled valves. Using my thumb on face of valves, the exhaust valve I can turn it a bit. but I cant turn the intake valve. but nothing has any oil on it right now.