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Briggs and Stratton ZZP really hard to turn over after rebuild

mike758

Registered
I have a 1949 Briggs and Stratton ZZP out of a Shaw Duall. The previous owner had the engine apart and said it had no compression, so I took the cylinder to a reputable machine shop to get measured. They ended up going .020 over, and I brought them the new piston assembly to test fit. Right now I have the cylinder and head installed to the engine. I lubricated the cylinder with a light amount of 2 cycle oil before installing the piston.

The issue I'm having now is the engine is extremely hard to turn over. I don't even have a plug installed, and I have to use a long socket wrench just to turn it. It's almost as hard to turn as the V8 on my pickup truck. I tried using my power drill to spin it and that didn't work. The lubrication system is a splash type, so I need speed to add more lubrication. I was wondering if maybe I should drip some oil down the spark plug hole, and put some oil on the valves through the side cover.
 

Heins

Subscriber
Last Subscription Date
01/02/2020
It sounds like the rod is too tight on the crankshaft. How tight did the piston fit in the cylinder? I think you better loosen the rod bolts a little and see if the engine will turn over easier. If it does, the rod bearing is too tight.
 

I like oldstuff

Registered
Last Subscription Date
11/09/2015
Rings not gapped and binding? Rod cap on backwards? Piston clearance?

That's about all it could be causing the problem.
 

mike758

Registered
The rods still the original rod, I never even took it out. The piston was really hard to slip on, so I'm thinking if there's no other contributing factor, maybe the machine shop didn't actually check, or maybe they overlooked it. It could also be due to the part being out of spec, I gave them the ring gap as described in the manual, but if the specs are different maybe there's some kind of variance there.
 

Motormowers

Subscriber
Age
55
Last Subscription Date
07/13/2019
Did you have the crank out and maybe used too thin a side cover gasket? It may not have any end play on the crank.
 

beezerbill

Subscriber
Last Subscription Date
01/10/2019
Try removing the rod cap and slide the piston all the way up, out of the way of the crank. Does the crank still spin stiff? If so, then the crank is binding, as already suggested, or something in the cam drive is binding. If the crank spins free, then take the piston all the way out and take the rings off. Put the piston back in, but don't tighten the rod cap all the way up. Leave it loose, about a full turn loose on each rod cap bolt. If the engine still binds then either the piston is too tight in the bore (which you might have noticed when putting it in in the first place - it should pretty much fall in without any rings on it) or you have a bent rod or a crooked bore. If it spins free then tighten the cap. If it binds now then either the cap is on the wrong way around or the big end is too tight for some reason. If everything spins free then probably the rings don't have the right end gap. I believe the end gap is probably around 12 thou but I don't have an exact spec. Also, check for dumb things like forgotten rags in the cam gears.

One trick I learned for putting engines together is to put everything together but with no rings on the piston. The engine should spin over freely - if it doesn't then it is time to go back in and find out what's wrong. I have found a lot of bent rods and even a few crooked bore cylinders that way.
 

Andrew Mackey

Moderator
Last Subscription Date
05/14/2017
As others have noted - pull piston and rod and try to spin the crank. If it is binding, check the gasket on the backing plate. It comes in different thicknesses, and if too thin, will bind the crank tight! You need a minimum of 1.5 to 2 thousandths end play. Any less and you will bind tighter than dicks hatband!
 

mike758

Registered
Ok, so I diagnosed it to definitely be the piston. I brought the cylinder down the bottom and unbolted the cylinder. The engine turns fine with the cylinder moving up and down with the piston. The biggest issue now is how to take the cylinder off. I pulled up while twisting back and forth and made absolutely no progress taking it off. I'm afraid I might have to try prying it.
 

gdstew

Registered
"The rods still the original rod, I never even took it out. "

From what I read, you removed the head and cylinder from the crankcase, removed and replaced piston with a .020" oversize piston. You did not remove the rod so it should be good on the crankshaft. Did the machine shop actually bore the cylinder .020" oversize or did they just say it was worn enough to put in a bigger piston???? I'm just guessing but I think the cylinder isn't as big as someone thought. There should be .007" to .015" ring gap according to B & S.

To remove stuck piston from the cylinder, try pulling cylinder up from the crankcase and stick a piece of wood on each side between them and turn crankshaft, pulling piston down. Lift back up, thicker pieces of wood, and try again. Hope this works!
 

mike758

Registered
The cylinder was definitely machined because I can see the marks. According to the manual, the ring gap should be .007-.015. Maybe they thought I meant .07-.15. Anyway, I'll bring it back. I think the woodblock idea is what I'll try
 

gdstew

Registered
For oversize, you take the standard bore and add .020" to it. You do not measure the piston and add X amount for oversize. That is not the way it is done in the small air cooled engine business.

If it is a 2" standard bore, you bore to 2.020"

If it is a 3" standard bore, you bore to 3.020"

B & S make their pistons to fit your bore, you do not fit your bore to their piston!
 

beezerbill

Subscriber
Last Subscription Date
01/10/2019
Did the machine shop have the piston when they bored the cylinder so that they could fit it properly? If not, then they may have bored the cylinder undersized, fully expecting you to bring the piston in so they could do a final hone on the cylinder for a proper fit. Or expect you to do that final hone. I have made this mistake myself - had a block bored by a local shop without the pistons in hand. They warned me that the cylinders would be undersized, and I or someone else would have to hone them to size once the pistons showed up.

If the piston is a proper fit but the rings weren't properly gapped, then they could be causing the binding.

As for removing it, try supporting the cylinder off the crankcase on a couple of 2 by 4's, and driving down on the piston with a hammer and another piece of wood on top of the piston. If it doesn't go pretty easy with only moderate hammering, then stop and figure something else out (what, I don't know) before you damage the piston.

Let us know how this turns out, and good luck!
 

gdstew

Registered
How would an engine company make engines if they had to fit the piston on every one going down the line? They didn't! B & S, Tecumseh, Kohler, Wisconsin, Clinton, they all were bored to a standard size. Same way with oversize. Bore + oversize. If your machine shop has to fit the piston, you better find somebody else. Question--what is the rate of expansion of a B & S piston vs a Kohler piston?
 

mike758

Registered
Well things couldn't have gotten any worse. I broke the rod trying to get the cylinder off the engine. Then after I got the piston out I discovered part of a zip tie was jammed in the oil ring (I used zip ties as sleeves). This could have been my issue all along, but I'm still unsure. The compression rings were really tight and they weren't effected. I have another engine at the shop so I'm going to have them recheck it either way at this point, especially now that I'm going to have to take the whole engine apart now to replace a rod.
 

Heins

Subscriber
Last Subscription Date
01/02/2020
You could take the rings off the piston and see how tight the piston without the rings fit in the cylinder. Put the rings in the cylinder and see how much end gap you have on the rings.
 

mike758

Registered
Just took the rings out and there's no gap! Tried to move just the piston and it doesn't move freely. Of course I broke the oil ring, when it rains it pours, right?
 

gdstew

Registered
That cylinder needs to be re-checked for size. Was that cylinder actually bored or honed and to what size, or was it simply hit with a deglazer
 

mike758

Registered
They said they bored it 20 over, and asked for the piston which I brought in. Obviously they didn't test fit it, unless they mistakenly used the old piston which they asked for when I first brought it in. It's going back tomorrow
 
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