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Small Air Cooled Gasoline Engines

Briggs and Stratton ZZP really hard to turn over after rebuild


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  #21  
Old 08-24-2017, 09:50:33 AM
beezerbill beezerbill is offline
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

Please - let us know what they find. Could be that the piston now has a burr or raised edge somewhere from all the "activity" it just saw which is why it fits tight. Or the shop didn't get it right. Should be easy to check. Piston without rings should fall right in, should be able to slip a strip of notebook paper between the piston and cylinder wall without much trouble. Whatever the specs are for the clearance, a feeler gauge that thickness should fit between the piston skirt and wall, at 90 degrees to the wrist pin, at the bottom of the skirt.

Rings straight out of the box are usually gapped pretty close but often need some touch-up. The fact that there is NO gap, along with the tight piston fit, points to the bore being too small.

Sounds like you will be looking for a rod.
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Old 08-25-2017, 07:24:31 PM
mike758 mike758 is offline
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

Ok I think I officially found the issue and I'm glad I caught it before I went back to the machine shop: the bottom of the piston is out of round. I discovered this because the piston slides in about half way top down, and doesn't fit at all bottom down. I most likely did this when installing the piston. This mistake adds up to be a $200 mistake, but I guess it's better to learn now then on an even more expensive engine
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  #23  
Old 08-25-2017, 08:18:27 PM
Charley K Charley K is offline
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

Mike, Pistons are not always round and some pistons have skirts larger than the top. I haven't a clue if that is true in this case. I really don't see how you could get it out of round unless you dropped it or beat in it. If it were a defective piston the shop would have found it when they were fitting it. I would have the bore checked to see if it is the same from top to bottom. I have bored many blocks and have seen several that had a taper fresh out of the machine shop. You should be able to put a .015 to .003 long feeler gauge on one side of the piston across from the piston pin. It should be snug but slide freely in the bore. The feeler gauge thickness will be determined by the piston to wall clearance. I think you will probably find the bore is out of spec. I see Beezerbill said about the same, I posted before I read his reply. My apologies. Well I need to edit again .0015 not .015.

Last edited by Charley K; 08-25-2017 at 09:39:54 PM. Reason: wrong size
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Old 08-25-2017, 09:34:51 PM
mike758 mike758 is offline
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

Well the only reason why I think I might have cause it was because when I installed the piston, I installed it by putting the cylinder over it while it was connected to the rod. I beat on the cylinder with a hammer on a block of wood, and the side of the piston was up against the block
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  #25  
Old 08-25-2017, 09:43:09 PM
Charley K Charley K is offline
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

That makes me think the bore size was wrong from the start, It should slide without the need of a hammer and wood block.
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  #26  
Old 08-25-2017, 09:54:11 PM
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

So it's gets back to check every thing for size and clearance and if the bore is true all the way down. Air cooled engines will wear to a taper more so than a liquid cooled engine. You should never have to drastically force things back together if the fit is correct. Another thing to watch for are some of those after market rings. I had a little Cub tractor that the parts place supplied rings for. Even tho they were the right size they were so stiff to compress that they basically got so tight that the starter wouldn't turn it over. we had to get the original cast type rings and cured the problem.
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Old 08-25-2017, 10:14:15 PM
Ken Karrow Ken Karrow is offline
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

Mike in post #18 that the rings had no gap, that may be the reason that the original fit was to tight. Agree that beating on the cylinder was not a good idea. Some machine shops may have the equipment to cam turn the piston to original specs. Back in the day you could buy pistons in oversize -semi- primarily for engines that were not common enough to carry exact oversizes. Industrial, tractor, and some older trucks. Anyway you ordered semi an turned them to the bore size you needed. Cam turned because many (most?) pistons are not round below the wrist pin. If I recall right semi were a little over .125 oversize and some low speed engines even bigger and not finished. Hence semi-finished.
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  #28  
Old 08-26-2017, 09:21:32 AM
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

Mike 758:
You need to rethink your strategy on engine assembly. Trying to get the cylinder to go on over the piston while it is still attached to the rod, which is still on the crank, which is still in the case is not standard procedure. Beating it down with a block of wood and a hammer is a good way to end up with broken rings, a bent or broken rod and, of course, a beat up piston.
Find a way to accurately measure your cylinder bore. Did the shop in fact bore it .020" over standard size? Buy or borrow a 6" dial caliper tool and know what your bore is.
Then assemble the cylinder to the crankcase. Assemble the rod to the piston. There are usually marks on the piston and on the rod that need to point certain directions. The assembled piston and rod are then lowered through the top of the cylinder and using a ring compressor tool or some thin sheet metal and a couple of appropriate sized hose clamps to compress the rings so the piston will slip into the cylinder without breaking the rings or scoring the cylinder walls. Attach the rod to the crankshaft last watching the alignment of the rod cap on the rod. There will be marks to show which way it goes. It is pretty easy to do it right, but just as easy to do it wrong and end up with broken parts and things that do not fit right. If you are not sure, ask.
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  #29  
Old 08-26-2017, 10:10:45 AM
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

Yes, trying to slide the barrel down over the piston with the piston assembled to the rod, etc, is a good way to invite disaster. The piston will try to cock over and not enter the cylinder straight - all you can do is try to keep nudging it straight until the piston is in well beyond the rings. However, on a lot of motorcycle engines this is the only way the engine can be assembled.

Whatever order you assemble the engine, you should need to supply only enough force to slide the ring compressor over the rings and the rings into the cylinder - some light thumping with the palm of your hand should be enough. No hammer needed.

Be sure to keep posting questions and asking for advice as you work on this engine. If you get stuck, think you are about to get stuck, or run into a situation you are not sure how to handle, ask us before you proceed. There is a lot of accumulated knowledge and folks willing to help here. Also, there are books on small engine repair - might be worth your time to find one or more of these and read through them.
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Old 08-26-2017, 06:09:07 PM
mike758 mike758 is offline
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

Yea I was aware that method was not the best, but I thought it would work better then it did. I did end up breaking the rod taking the piston out so now I have no excuse to try that again. Next time I plan to keep the rod in the motor, but work the piston into the cylinder beforehand just far enough so I can install the piston pin. The thing that make this hard is the engine isn't easy to pull on this tractor. The flywheel doesn't fit out of the clutch housing, and the clutch housing is built into the tractor. I would need to get a puller on the flywheel, but the only way to do so would be by removing the transmission. Luckily I'm able to take the oil pan off, and install the rod from under the tractor

---------- Post added at 06:09:07 PM ---------- Previous post was at 06:06:42 PM ----------

Just to clarify, the piston fits in halfway putting it in top first, but doesn't fit at all bottom first. I've done a lot of business with this machine shop so remeasuring won't be an issue, but I just wanted to check myself first
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  #31  
Old 08-26-2017, 07:27:18 PM
Kirk Taylor Kirk Taylor is offline
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

Quote:
Originally Posted by mike758 View Post
Yea I was aware that method was not the best, but I thought it would work better then it did. I did end up breaking the rod taking the piston out so now I have no excuse to try that again. Next time I plan to keep the rod in the motor, but work the piston into the cylinder beforehand just far enough so I can install the piston pin. Luckily I'm able to take the oil pan off, and install the rod from under the tractor.
If you are able to hook up the rod from underneath, why are you still planning to attach the piston after the rod is installed? Why are you not assembling the piston to the rod, inserting the piston into the cylinder from the top, installing the cylinder assembly, then hooking up the rod? If you insist on installing the rod first, at least put the piston in from the top and push it to the bottom.
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  #32  
Old 08-27-2017, 12:47:49 PM
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

"....Yea I was aware that method was not the best, but I thought it would work better then it did. I did end up breaking the rod taking the piston out so now I have no excuse to try that again. Next time I plan to keep the rod in the motor, but work the piston into the cylinder beforehand just far enough so I can install the piston pin...."

"....Luckily I'm able to take the oil pan off, and install the rod from under the tractor...."

If you are able to install the rod correctly, why would you even consider trying to do what you propose when it ended so poorly the last time? You seem intent on making the job harder and more likely to end with more broken and/or damaged parts.
I think a fair question at this point is:
How much experience do you have with small engine repair? All indications so far say "Not Much". Please consider listening to the good advice presented here by various posters. Most of us have been doing this (correctly) for a long time.
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  #33  
Old 08-28-2017, 10:03:39 AM
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

Mike 758,

In light of all I have read about your engine repair fiasco, the money you spent and all you have to show for it, your seeming inability to comprehend or unwillingness to accept the sensible and tested advice you have received, I suggest you box up all of your parts, take them to the machine shop that bored your cylinder, and pay them to reassemble the engine properly. Had you done that at the outset you'd have a happily running engine now, instead of a bunch of greasy parts. Don't feel bad, this sort of thing is not for everyone. I'm sure you will be much happier knowing your engine was properly reassembled and good for years of service instead of wondering forever where that extra bolt or flat washer was supposed to go.
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Old 08-28-2017, 07:04:55 PM
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

I will do it the right way now. The reason I did it the way I did the first time was to save time and a headache. All that needed replaced was the bore, so why bother taking the rod out? But obviously I learned my lesson here and won't do it again. The only reason I was thinking install piston halfway in cylinder and attatching to rod the second time was due to difficulty in trying to work under it. But I looked at it again and I should be ok to do it properly. I've done a lot of engine work and I'm actually rebuild a Farmall Cub C60 as well which is going better. This is my first time replacing a piston though, besides the farmall cub, and I did indeed overestimated the job
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  #35  
Old 09-16-2017, 10:40:31 AM
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

Ok, so just an update, I just got another piston in today and that was indeed the issue. The new piston slides up and down easily. Right now I'm finishing up the engine on my farmall cub, but once I'm done that I'll redo this the right way and post an update when I'm done
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  #36  
Old 09-16-2017, 12:41:16 PM
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

Keep us posted as you go. Pictures would be nice if you can get them.
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  #37  
Old 10-05-2017, 09:15:40 PM
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

I attached a picture of the engine I’m working with for reference. I was able to turn the oil pan and give myself enough room to remove the rod. The oil ring on this new piston was super brittle and broke without barely stretching it, so I have another one coming in tomorrow. So I should be set mechanically soon, the magneto is going to be the next challenge.
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Old 10-09-2017, 09:44:59 PM
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

Ok I have a question and figured I’d ask this time. The rings need to be gapped, and I want to avoid buying the tool if possible just because this would probably be the only time I use it. I was wondering if using a Dremel or die grinder with a grinding wheel would suffice? I do have 6 compression rings so I do have some to spare
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Old 10-09-2017, 11:37:13 PM
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

The top ring should have an inside bevel, the middle ring has an outside scraper. I know you like your machine shop, but I don't remember you ever telling us that the cylinder was actually bored to B & S specs, or if they just used theirs. If bored to spec and using B & S rings, you shouldn't need to gap the rings. I still think you have an incorrect bore and having to gap the rings tells me so.
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Old 10-10-2017, 04:06:49 AM
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Default Re: Briggs and Stratton ZZP really hard to turn over after rebuild

If they are iron rings you can just use a really fine file. Go slow and keep the file square. If they are chrome rings - same idea but with a fine diamond file. Usually don't have to take much, if any, off.

What's your clearance between the bottom of the skirt and cylinder wall? Should be easy to measure with a feeler gauge.
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