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

[warreng5995]

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...

 

[ILENGINE]

Some oil in the line to the fuel pump may be normal due to no way to stop oil from getting into the line.. the power issue and non restarting could be a partially sheared flywheel key.

 

[Bellcrank]

Did you ever run this engine before tear down ? Sounds like it's been rode hard and put away wet. Maybe it's worn out. Bore Diameter 3.4365 in. (87.29 mm) / Bore reject 3.4395 in. (87.36 mm) / Bore Out-Of-Round .0015 in. (.04 mm)

 

[Born2Mow]

Did you replace the fuel pump vacuum line with new "SAE J30 fuel hose" while you were re-assembling everything ? It's common that after 20 years this vacuum line has small leaks in it. Small leaks turn the vacuum hose into an impromptu "breather hose", and would allow crankcase oil into the hose. Small leaks in this hose will also keep the engine starved for fuel because the pump is not working with full pumping force. This would explain the engine's "low power" condition.

After 20 years on an air-cooled engine all your "rubber" parts are going to be shot. This list commonly includes hoses, o-rings and oil seals. First they harden. Then they crack. Then they leak.

 

[StarTech]

With a 2000 engine it should have been mic'ed. Most likely the cylinder is both tapered and out of round which means that it need to go to .020 over if it was worn pass this. Just using a flex hone is also a mistake as it only makes things worst. Plus did you make sure you ordered the correct rings as they changed them in April 2001?

Side note the service manual still has the old cylinder torque spec of 220 in-lbs and the current torque spec is now 250 in-lbs. You also pay special attention the web area between the cylinder and the push rod galley as this where these engines blow head gaskets commonly.

 

[warreng5995]

Hi all thanks for the replies. Didn't get any emails that anyone had replied.
Anyway, try to answer everyone:

Some oil in the line to the fuel pump may be normal due to no way to stop oil from getting into the line.. the power issue and non restarting could be a partially sheared flywheel key.

I'm not sure how oil is the line is normal, I thought that is what the crank case breather was supposed to stop? Also if there is enough oil to block the line wouldn't that stop, or at least hinder, the vacuum to run the fuel pump? In which case would either cause no fuel to get through, or possibly cause the engine to run lean?
I tried my very best to assembly the flywheel and key very carefully, and torqued it to spec. I don't think that is the issue, as when it is cold, it starts right up fine. But I will look at it if I take the engine covers back off.

Did you ever run this engine before tear down ? Sounds like it's been rode hard and put away wet. Maybe it's worn out. Bore Diameter 3.4365 in. (87.29 mm) / Bore reject 3.4395 in. (87.36 mm) / Bore Out-Of-Round .0015 in. (.04 mm)

Yeah, we ran it for a couple seasons. Did all maintenance when we got it, and changed oil and filters regularly. Never saw the sludge and other until I took it apart though. My Dads nephew (my cousin) bought it from an auction... and yes there were issues from the beginning, but most seemed small and I was able to keep it running. The one that I couldn't fix was a light "knocking" or pinging sound. Part of it ended up being the spot welds holding the baffle inside the muffler had broke, I cut it open rewelded it, and welded the muffler back together (that was about 2 years ago when we first got it). Thought that had taken care of the sound, but could still hear a light pinging coming from the crankcase. It doesn't seem to have this sound now though. The bore being out of spec could be possible. I didn't measure it, as I didn't really have any tool that could do so. A T-Bore hole gauge would have worked, but don't have one and didn't realize at the time that some cheapos could be found.

Did you replace the fuel pump vacuum line with new "SAE J30 fuel hose" while you were re-assembling everything ? It's common that after 20 years this vacuum line has small leaks in it. Small leaks turn the vacuum hose into an impromptu "breather hose", and would allow crankcase oil into the hose. Small leaks in this hose will also keep the engine starved for fuel because the pump is not working with full pumping force. This would explain the engine's "low power" condition.

After 20 years on an air-cooled engine all your "rubber" parts are going to be shot. This list commonly includes hoses, o-rings and oil seals. First they harden. Then they crack. Then they leak.

I did replace the vacuum line, as well as all other fuel lines. But not with SAE hose, I used transparent silicone fuel hose. Thats why I could see the oil in the line. With oil going into that line, I also thought that it blocking the vacuum to the fuel pump could be part of the power issues. I did replace all gaskets, all seals, and etc with all brand new. As you said, 20 years old all those type parts are going to be hard and cracking.

With a 2000 engine it should have been mic'ed. Most likely the cylinder is both tapered and out of round which means that it need to go to .020 over if it was worn pass this. Just using a flex hone is also a mistake as it only makes things worst. Plus did you make sure you ordered the correct rings as they changed them in April 2001?

Side note the service manual still has the old cylinder torque spec of 220 in-lbs and the current torque spec is now 250 in-lbs. You also pay special attention the web area between the cylinder and the push rod galley as this where these engines blow head gaskets commonly.

The new rings were the correct part number as per the engine date code according to B&S, and they are B&S brand rings too. I didn't even know they sold oversized rings for these... manual never mentioned it and I hadn't replaced rings on a small engine before. Yeah, I should have found a way to measure the cylinder bore. As I said up above, didn't have the tools, didn't know I could have gotten some cheap, and also there are no machine shops out here so had no where to get it measured either.
I didn't know about the torque spec change, I'll have to go look at the service manual I have and see the spec it gave, as that is the torque I set it too. And if I remember right, I *believe* it was 220. If that it what the manual I have states, I'll step it up to the 250 see what that does. I had thought about going higher recently, but didn't want to strip the threads out of the block. If they raised the torque spec, then compression leakage is most likely why they would have done so.
And yes that web area is the weakest point of these OHV gaskets. Just replaced one on another mower that I got for free as it would put out a literal cloud of smoke that you couldn't see through (due to the blown head gasket), and that is exactly where it blew out too. That mower doesn't have a mower deck, but since fixed it works great to pull my yard trailer I built

Additional Question: Is there a way to know if the muffler is partially blocked??? I read somewhere that this could cause similar issues. But it appears that the exhaust flow is normal. I may just pull the muffler off and see what happens.

Thanks for all the input and information everyone. I will go through some of these tomorrow if I have time to work on it. Once I go through the list, I'll report back if anything changed for better or worse.

 

[StarTech]

The only thing I had clogged mufflers on has been 2 cycles but anything can happen.

Yes the manual wasn't written with a novice in mind. If in the rear you will find that if cylinder has .004" of wear over the standard cylinder size you need to hone it to .020 over. As said this cant done with a flex but is instead done using a rigid hone with the correct stones. Ridge hones prevents the stones from just following the current taper and/or oval.

Aluminum cylinders 280 grit (nothing of coarser grit). Cast iron lined 180 grit (can use 80 grit for quick take to near .015 over then switch to 180 grit). You must create a crosshatch pattern of 45 degrees. Also while honing keep the rpm down under 300 rpm especially with aluminum to prevent galling and use honing oil. Smaller the diameter the slower.


If it does comes to oversizing then you will need both the OS piston and ring set.

 

[Born2Mow]

I did replace the vacuum line, as well as all other fuel lines. But not with SAE hose, I used transparent silicone fuel hose. That's why I could see the oil in the line. With oil going into that line, I also thought that it blocking the vacuum to the fuel pump could be part of the power issues. I did replace all gaskets, all seals, and etc with all brand new.

• No experience with that type hose, but even if it only lasted a month there should be no vacuum leaks and the "low fuel delivery due to loss of vacuum" reduced to a non-issue. Still could be a tiny hole in the pump's diaphragm, but the I agree the hose should be 100% fixed. Good call.
• Oil in the clear hose is not a sign of anything, other than that the hose is connected to the engine's sump.

That's all I got.

 

[warreng5995]

The only thing I had clogged mufflers on has been 2 cycles but anything can happen.

Yes the manual wasn't written with a novice in mind. If in the rear you will find that if cylinder has .004" of wear over the standard cylinder size you need to hone it to .020 over. As said this cant done with a flex but is instead done using a rigid hone with the correct stones. Ridge hones prevents the stones from just following the current taper and/or oval.

Aluminum cylinders 280 grit (nothing of coarser grit). Cast iron lined 180 grit (can use 80 grit for quick take to near .015 over then switch to 180 grit). You must create a crosshatch pattern of 45 degrees. Also while honing keep the rpm down under 300 rpm especially with aluminum to prevent galling and use honing oil. Smaller the diameter the slower.

View attachment 55788View attachment 55789
If it does comes to oversizing then you will need both the OS piston and ring set.

I've rebuilt car engines and such, so I understand the procedures. I also did a bit of research on the differences for a small engine as well. I just wasn't going to go have it bored out if it was off. But I should have measured it to see how far out of spec it was, as if it was too far then I should have just junked the mower. The only reason I even did the engine rebuild, is because of all the other work I had already put into the mower.

 

[warreng5995]

• No experience with that type hose, but even if it only lasted a month there should be no vacuum leaks and the "low fuel delivery due to loss of vacuum" reduced to a non-issue. Still could be a tiny hole in the pump's diaphragm, but the I agree the hose should be 100% fixed. Good call.
• Oil in the clear hose is not a sign of anything, other than that the hose is connected to the engine's sump.

That's all I got.

Its the type of line often used on trimmers, chainsaw, etc. They just use a much smaller size. In any case, I know there may be oil vapor/residue in the line. But I think I'm getting so much oil in the line that it is slowing the vacuum to the fuel pump. With the engine off, there is about 1" of oil (in length) in the lowest part of the line. In any case, if that's not the issue then hopefully its one of the other things that I can fix.