Small engine repair

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This question may not exactly fit this forum but there seems to be some pretty good answers on most subjects so here goes. I have a old Bolens garden tractor with a 16hp Briggs and Stratton engine.The motor is a twin cylinder horizontal shaft. Last year it started smoking and using lots of oil.I need to rebuild it before time to cut grass again.I have rebuilt a couple of car engines so I know the basics,but this will be my first experience on a 4 stroke.Can I just replace rings and gaskets as there are no rod bearings. If any one has any advice,dos and don'ts,or any other sugestions they would be appreciated!

-- BamaJohn (jjjn@bellsouth.net), February 03, 2002

Answers

I got a Briggs manual from our local library when I rebuilt my 12 hp garden tractor engine. I would suggest you play it safe and check out a manual.

-- Jay Blair in N. AL (jayblair678@yahoo.com), February 03, 2002.

This link has a lot, 101K, of information on small engine repair. It does not give specs, just general dos and don’ts information, General Repair Information, http://www.repairfaq.org/REPAIR/F_lmfaq.html#lmengdis

-- BC (desertdweller44@yahoo.com), February 03, 2002.

John if you have rebuilt a car engine, this is NOT your first attempt at a 4 stroke engine. 99.9% of all automobiles built within the last 3 decades have all had 4 stroke engines. Most of them are not air-cooled any longer though (long live the Beetle).

I am sure I am gonna be "poo-pooed by some but IMHO you need to replace the engine if the machine warrants the price of a new engine. So often a replacement can be found on eBay at a good savings and can be adapted to your application with very little effort (much less than what you will spend on what I am about to tell you to do). If you choose to rebuild overhaul yours, there are a couple of things you can do to yours to maybe get another season or two from it.

If it is smoking and burning oil, most likely it is absolutely worn out. When you pull one of the cylinder heads off I feel certain you will see a major ring at the top where the piston rings do not travel all the way to the top. If your fingernail catches the lip, then you will need to remove the ridge with a ridge reamer before the piston can come out.

Now this is where you are gong to find your problem. If the piston is worn too, then you really need to bore then engine case (both cylinders) for oversized piston however most engines today are concidered "throw-aways" by the mfg. and they do not offer any oversized replacement pistons. Just re-ringing it will cause piston slap and piston galling which will cause the engine to not make optimum horsepower. Also with the piston rocking in the cylinder you will find the rings do not wear correctly and you have a tough time making them seal (more hp loss and hard to start due to lack of compression) so you very quickly find yourself with the same problem. If you can find someone who has a machine shop that can knurl your piston skirt area to help "take up the slack" this will help some. The other choice you have is to get the block bored and new sleeves installed to bring the cylinder bore back to standard diameter. Then you just buy 2 new pistons and rings.

As for the bottom end. The aluminum rods can be repaired but again this is a "shadetree way" of doing this. You can buy "PlastiGage" at NAPA or at your FLAPS (Friendly Local Auto Parts Store) and use this to check the clearances between the crankshaft journal and the rod itself. Basically this is a piece of plastic thread that is crushed by re-installing the rod onto the crank. When the cap is removed you check the threads "flatness" to see how much if was crushed. The flatter it is the tighter the oil clearances.

Since you are dealing with aluminum, you might be able to "tighten" the rod up a bit by placing a piece of 320 grit sandpaper face-up on a glass table and "lap" the rod cap mating surface just a bit to take up the slack. Remember that you are dealing in .001 thousandths here so just one figure 8 swirl should take off enough. This will make the con rod large end not perfectly round but the roundness needs to be true on the thrust side (the rod side - not the cap side) and I assure you the rod cap will become friendly with the crank in due time.

I hope this helps you some in your endevor but realize that you are truly "McGuyvering It" when you try to band-aid it this way!!

-- BRENT in 10-uh-C (bt@nospam.com), February 03, 2002.


Alot of good advice from the other respondents but my guess is that if this an old Bolens it likely has at least a cast iron sleeve if not an entirely cast engine, thus making it less "disposable" and more rebuildable. Being the cheap guy I am I'd try to rebuild it before trying to buy a replacement.

What I've foud regarding auto parts stores is for the common stuff they're OK but if I have a technical problem I take it to a place that specializes in engine rebuilding. They can get all kinds of odd sized pistons and can mix and match to suit your requirements.

-- john (natlivent@pcpros.net), February 03, 2002.


Do the valve faces also, knurle the guides if you have a knurleing tool, grind the valve clearance to .006 intake, .008 for exhaust. Place the rings into the cylinder, square them with the piston, .002 ring end gap per inch diameter; deglaze the cylinder with a ball hone; attached to a slow drill with fluid. Use an alternate tighten pattern for the head bolts, do the three stage tightening pattern - 50 - 55 - 60 lbs, happy moweing.

-- mitch hearn (moopups@citlink.net), February 03, 2002.


In response to some answers , I believe the entire block is cast.Also I can just barrrrrrrly catch the ring groove at the top of the cylinder with my fingernail.If there was no knocking can I just bolt the rod caps back on.My parts book list std,10,20,and 30 os pistons and rings.Do I replace with standard or something oversize to compensate for the wear.Thanks for all comments.

-- BamaJohn (jjjn@bellsouth.net), February 03, 2002.

My husband has used this web site - maybe it will help you too - hope so!

http://repairfaq.org/REPAIR/F_lmfaq.html

-- hmm (h.m.metheny@att.net), February 03, 2002.


After you run the ball cylinder hone, do you still have the ridge? If no, run the .010 rings with the ring clerance gap as above on you standard pistons that you have. If the ridge ring is still there, bore the cylinder to accept the .010 over pistons.

-- mitch hearn (moopups@citlink.net), February 03, 2002.

Briggs and stratton has a web site where you can ask questions and they answer them pretty quick it's briggsandstratton.com go to faqs( frequently asked questions). its very helpful

-- Keith (peepee125@hotmail.com), February 04, 2002.

You said the motor started smoking and using oil last year. Did it start suddenly? If it did your only problem could be a stuck oil ring. If you still have the engine together try checking the compression. If it is around 130 psi or better your compression rings are ok. I have put penetrating oil in the top of the cylinder and let it set then roll the engine a few times to get the penetrant out, THEN CHANGE THE CRANKCASE OIL, and try it. This may unstick the oil rings. If not then you must go into it. Still could be just a stuck oil ring.

-- Dave (drcomer@rr1.net), February 06, 2002.


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