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Bolens Husky 750 oil leak


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#16 dtsh OFFLINE  

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Posted July 13, 2016 - 02:21 PM

I've got a valve spring compressor, the job would have been a real pain without it. The suggestion to use magnets to replace the valve keeper is wonderful, I hadn't thought of it but I am certainly going to try it as I can see replacing those is going to be very un-fun.

 

Lapping the valves was part of the plan before putting it all back together. I wish I knew how many hours were on it since it's last major service as that would really help determine if this is 49 years worth of gunk, a couple years, or a couple of hours. A bit more testing shows the cylinder does leak pressure, but I am unsure for how long a B&S 170401 should hold compression. If I seal up the head and turn it for compression, I can hear the air in the cylinder slowly escaping into the crankcase. The repair manual suggests that if it holds long enough to make compression (i.e it bounces when turned), it's good, but if this is an issue I'd rather resolve it now. I am wondering if there isn't some wear to the cylinder after all, any advice?


Edited by dtsh, July 13, 2016 - 02:29 PM.


#17 MailmAn OFFLINE  

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Posted July 13, 2016 - 03:00 PM

A bit more testing shows the cylinder does leak pressure, but I am unsure for how long a B&S 170401 should hold compression. If I seal up the head and turn it for compression, I can hear the air in the cylinder slowly escaping into the crankcase. The repair manual suggests that if it holds long enough to make compression (i.e it bounces when turned), it's good, but if this is an issue I'd rather resolve it now. I am wondering if there isn't some wear to the cylinder after all, any advice?


I am not 100% certain on these small B&S engines myself. I don't know if they leaked compression when they were brand new or if everything should be nice and tight and it should hold compression just like a modern car engine or something. My gut instinct says that if it is leaking compression into the crankcase though, that is not good and tells me that the compression ring is worn out on your engine. Crankcase pressure build-up is also not good for your engine and will cause it to push oil out of the seals and gaskets (which I think was part of your problem in the first place, right?). If it is bad enough, I have even seen engines push oil out of the dipstick tubes because of excessive crankcase pressure build up.

If you're this far into it anyways with the teardown, I would highly suggest getting new rings for it and honing out the cylinder at least. It's up to you if you'd want to try to bore it out at all and get oversized rings for it. (Depending on how far you overbore it though, I don't know if you will need a new piston for it that is designed for an over-bored engine or not. Do they even sell these for B&S engines?) I have never tried to bore out a small engine before myself, so... I know on like a Chevy 350 though, you need to get .030" over pistons and rings if you bore out your block .030". I'd imagine the same concept applies to a single cylinder small engine as well.

Edited by MailmAn, July 13, 2016 - 03:03 PM.


#18 Bruce Dorsi ONLINE  

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Posted July 13, 2016 - 05:47 PM

I've got a valve spring compressor, the job would have been a real pain without it. The suggestion to use magnets to replace the valve keeper is wonderful, I hadn't thought of it but I am certainly going to try it as I can see replacing those is going to be very un-fun.

 

Instead of using a magnet, I prefer using a flat-bladed screwdriver and some grease.  ....Apply a dab of grease to the inside of the split keeper, then use another dab of grease on the outside of the keeper to stick it to the blade of the screwdriver,  (The small end of the keeper goes UP.) ....With the spring and retainer compressed at the top of the valve chamber, insert one keeper and "stick" it to the valve in its proper location.  ....Now do the same with the other keeper. 

 

When you are sure that the keepers are in their proper position, slowly lower the retainer over the keepers and release the spring tension.

 

When installing the valves, make sure the valve lifter is in its lowest position.

 

While this may sound difficult, it took me longer to type this than it would take to install that valve !! 

 

Lapping the valves was part of the plan before putting it all back together. I wish I knew how many hours were on it since it's last major service as that would really help determine if this is 49 years worth of gunk, a couple years, or a couple of hours. A bit more testing shows the cylinder does leak pressure, but I am unsure for how long a B&S 170401 should hold compression. If I seal up the head and turn it for compression, I can hear the air in the cylinder slowly escaping into the crankcase. The repair manual suggests that if it holds long enough to make compression (i.e it bounces when turned), it's good, but if this is an issue I'd rather resolve it now. I am wondering if there isn't some wear to the cylinder after all, any advice?

If the cylinder bore is in as good condition as you described, it is probably not worn much, if any.  ...Piston rings may be worn, but if the engine wasn't smoking while running, they may not be worn much, either.


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#19 dtsh OFFLINE  

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Posted July 13, 2016 - 08:05 PM

I am not 100% certain on these small B&S engines myself. I don't know if they leaked compression when they were brand new or if everything should be nice and tight and it should hold compression just like a modern car engine or something. My gut instinct says that if it is leaking compression into the crankcase though, that is not good and tells me that the compression ring is worn out on your engine. Crankcase pressure build-up is also not good for your engine and will cause it to push oil out of the seals and gaskets (which I think was part of your problem in the first place, right?). If it is bad enough, I have even seen engines push oil out of the dipstick tubes because of excessive crankcase pressure build up.

If you're this far into it anyways with the teardown, I would highly suggest getting new rings for it and honing out the cylinder at least. It's up to you if you'd want to try to bore it out at all and get oversized rings for it. (Depending on how far you overbore it though, I don't know if you will need a new piston for it that is designed for an over-bored engine or not. Do they even sell these for B&S engines?) I have never tried to bore out a small engine before myself, so... I know on like a Chevy 350 though, you need to get .030" over pistons and rings if you bore out your block .030". I'd imagine the same concept applies to a single cylinder small engine as well.

 

Perhaps I should get new rings and hone it, at least, while I've still got it torn down.

 

 

If the cylinder bore is in as good condition as you described, it is probably not worn much, if any.  ...Piston rings may be worn, but if the engine wasn't smoking while running, they may not be worn much, either.

 

No smoke when running, in fact it started and ran very well.



#20 Bruce Dorsi ONLINE  

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Posted July 14, 2016 - 08:28 AM

Perhaps I should get new rings and hone it, at least, while I've still got it torn down.

 

 

 

No smoke when running, in fact it started and ran very well.

 

I'm not a fan of honing an aluminum bore, unless absolutely necessary to remove scratches. ...B&S does not recommend it, either.

 

If you carefully remove the piston rings from the piston, put them into the cylinder (one at a time) and push them half-way down the bore, you can check the end gaps using a feeler gauge.

 

If the end gap for the compression rings is greater than .035" and the end gap for the oil ring is greater than .045", the rings should be replaced.

 

If your end gaps are less than specified, I would carefully re-install them, and put the engine together.  .....You will need a ring compressor to re-install the rings in the block.  ...A hose clamp will work if care is exercised.


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#21 secondtry OFFLINE  

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Posted July 14, 2016 - 09:40 AM

   Bruce is correct, checking the end gap is important. This can give you an indication of the amount of wear on the rings. Also checking it in 3 different locations  Top Center and Bottom of the cylinder will give an indication of cylinder wear. A perfect cylinder  Will have the same ring end gap through the entire stroke. Also check for a ridge at the top of the Cylinder. If the rings have worn the cylinder there will be a space at the top of the cylinder where the rings don't reach, this should be essentially original size. If you can feel a ridge with your finger nail and it is not just carbon it is likely a problem. If there is no ridge and the end gap is even the cylinder is perfect and it can only get worse with work.  Don   


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#22 secondtry OFFLINE  

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Posted July 14, 2016 - 09:44 AM

  Forgot to mention when installing the rings on the piston it is recommended that you make sure the gaps at the ends of the rings don't line up> Don 



#23 dtsh OFFLINE  

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Posted July 14, 2016 - 04:06 PM

I found a copy of a more recent repair manual, "CE8069 - Service Manual for Out of Production Engines 1919 - 1981" and am using it now as well as "270962 - Single Cylinder L-Head", which I believe should be the most specific manual for the 170401.

 

I pulled the piston out and removed the rings to check them for end gap. The top and middle ring both read 0.032, at the top middle and bottom of the cylinder, which according to the manual is within tolerances (0.035 reject). The oil ring gaps to 0.062 which the manual says to reject at 0.045, so it looks like I'll be needing new rings.

 

I presume an oversize piston would have a mark on it to indicate such, but I don't see any obvious indication and can't see in either manual a way to check. I don't suspect this has been rebored, but it's had nearly 50 years of (ab)use before me. Anyone have a hint?


Edited by dtsh, July 14, 2016 - 04:10 PM.

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#24 Bolens 1000 ONLINE  

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Posted July 14, 2016 - 04:19 PM

I found a copy of a more recent repair manual, "CE8069 - Service Manual for Out of Production Engines 1919 - 1981" and am using it now as well as "270962 - Single Cylinder L-Head", which I believe should be the most specific manual for the 170401.

 

I pulled the piston out and removed the rings to check them for end gap. The top and middle ring both read 0.032, at the top middle and bottom of the cylinder, which according to the manual is within tolerances (0.035 reject). The oil ring gaps to 0.062 which the manual says to reject at 0.045, so it looks like I'll be needing new rings.

 

I presume an oversize piston would have a mark on it to indicate such, but I don't see any obvious indication and can't see in either manual a way to check. I don't suspect this has been rebored, but it's had nearly 50 years of (ab)use before me. Anyone have a hint?

 

 

Any oversize piston is always marked, standard is usually a "o"  "STD" or completely blank

Just clean the top part real good sometimes they are stamped light


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#25 dtsh OFFLINE  

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Posted July 14, 2016 - 04:23 PM

Any oversize piston is always marked, standard is usually a "o"  "STD" or completely blank

Just clean the top part real good sometimes they are stamped light

 

The top, as in the top face, or the top portion of the cylinder of the piston? I looked pretty carefully and saw no marks at either location, but I'll recheck (and re-re-re-check if necessary).

 

Thanks everyone.



#26 Bolens 1000 ONLINE  

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Posted July 14, 2016 - 04:30 PM

Here's an example of a .030+

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#27 dtsh OFFLINE  

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Posted July 14, 2016 - 04:33 PM

Thanks, that makes it clear. There's no marking anything like that on this one and the original machining marks are still quite visible.

 

 

Any recommendations of what to use to remove the carbon on the various parts?


Edited by dtsh, July 14, 2016 - 04:34 PM.


#28 MailmAn OFFLINE  

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Posted July 15, 2016 - 10:15 AM

Any recommendations of what to use to remove the carbon on the various parts?


I would say carb cleaner (either spray or dip) or if you have a parts washer available, you could try to soak it in that. Just let them completely air dry out before you reassemble it. I don't think either of those two methods should hurt the piston or valves at all. Thoughts?

You could also lightly sand the top and sides of the piston with very fine grit sandpaper (like 400-500 grit, then again with 800-1,000 grit to make it nice and smooth). Just be sure you're only cleaning off the carbon deposits and not taking off a lot of material from the actual piston.

Edited by MailmAn, July 15, 2016 - 10:16 AM.


#29 29 Chev ONLINE  

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Posted July 15, 2016 - 10:46 AM

I would not recommend using sandpaper as particles of sand from the paper may embed themselves into the parts (such as the top or sides of the piston) as you are sanding and be released at a later date when the engine is running causing abrasive sand to be released in the combustion area - just my opinion.  I would suggest a hand wire brush on the carbon deposits or a wire brush in a drill but as stated be gentle - I would not recommend wire brushing the sides of the piston - scrape the ring groves gently with a small flat screwdriver or take an old toothbrush and square off the end of the handle to fit in the ring groove.  You could also sharpen the handle of another old plastic toothbrush with a file or grinder and then use it as a plastic scraper for the top of the piston and other areas.  After you clean the deposits off the parts make sure you scrub the parts with very soapy water a few times - the soap will suspend any dirt particles off of the material they were attached to, rinse off with water, wipe off with a clean cloth and then blow dry each time.  Once you are done cleaning coat the parts with clean engine oil to prevent any rust.  One of the biggest mistakes people make is failing to flush out the minute dirt particles that get created when residue in an engine is disturbed either from cleaning or machining operations such as cylinder honing - again just my opinion.    


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#30 crittersf1 OFFLINE  

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Posted July 15, 2016 - 11:03 AM

When checking the ring end gap make sure the rings are square in the bore






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