Blown Briggs and Stratton Twin Question

5412 Views 15 Replies 10 Participants Last post by green dream machine, Nov 21, 2019

AYP123

Discussion Starter · Jul 27, 2019

I recently acquired a 2001 Craftsman LT1000 w/ a 21 Horsepower Briggs Opposed Twin, very similar to a mower I used to own. I went to take a look at it yesterday and found that the engine was blown w/ no compression. I looked at the oil and there was none. I was sad to see mower like this die because I know that the opposed twins are becoming harder to find these days. This one in particular is the 461707-0147-E1 which is a higher end model of the opposed twin with a high output. I'd like to save this mower if possible. What are your thoughts on getting the engine rebuilt? I will also note, that no pieces of the engine escaped outside the block and there are no traces of oil from the engine on the outside. From my knowledge, when these blow it tends to be catastrophic because the rods and pieces that blow collide with the others on the other side. I don't know how much damage was done as I have not opened it up, but I know that there is no compression what so ever as the engine continues turning for a long time even after it stops cranking. If any of you know where to find rebuild kits also, please let me know. It would be very helpful. Thanks.

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dougand3

· #2 · Jul 27, 2019

Never opened one up, so not much help. First, I'd pull both plugs and see if there is any piston movement by rotating flywheel by hand. If it continues to turn a long time - are pistons disconnected from rods? Rods from crank? Both rods broken?
I was gonna rebuild a 6.25hp Tecumseh LEV115 until I saw they wanted $40 for a ring set. PHFFFT on that. Same with a Briggs pressure washer engine - oil slinger, camshaft, gaskets were $70. They price rebuild parts so high, better to buy a good running engine. Maybe the Opposed Twin parts are reasonable.

Cannon51

· #3 · Jul 27, 2019

I don't know if you can get to it with the engine in the frame but there is an access plate on the back of the opposed engines. If you can get that off and see inside that's probably going to tell you how much damage there is.

Walt 2002

· #4 · Jul 27, 2019

Yeah, you need to do some checking as above. Unusual for both rods to go at once. Owner MAY have been running it on one cylinder until it also went. Sounds like both are gone.

As for rebuilding, you will have to open it up before you know for sure. Main concern will be the condition of the crankshaft. Also check the camshaft for possible bend and camshaft bearing bosses for cracks. I have not worked on them for some time but I would check Maple Groove Distributing for parts then Stens. There were not that many 46 series made so parts may be a problem.

Walt Conner

AYP123

Discussion Starter · #5 · Jul 27, 2019

Thanks for the replies. I completely forgot about the access panel in the back of the engine. I plan on pulling the engine off and taking a look inside that way as the tractor has work that needs done that involves the engine being off. I also wanted to know, what can you do from the door in the rear? Can you remove pistons or no? Thanks again.

RedOctobyr

· #6 · Jul 28, 2019

I have a Briggs opposed twin, but fortunately haven't needed to dig into the lower end! From the pic that Cannon51 posted, it looks like the near-side connecting rod bolts (at the crankshaft) are accessible. If you could also reach around the crankshaft to the far-side rod bolts, then perhaps you could undo the connecting rods, and remove the pistons, with the cylinder heads off?

Before diving into the guts, I'd do the quick check to see whether the pistons are moving. As Walt said, it seems odd for both connecting rods to go at the same time, though if they are broken, it's lucky that nothing punched a hole in the block.

It's possible (albeit maybe unlikely) that a valve(s) is stuck open on each cylinder, and that's why there's no compression. It's easy enough to check for piston movement, and would tell you more about what you're up against.

Walt 2002

· #7 · Jul 28, 2019

"It's possible (albeit maybe unlikely) that a valve(s) is stuck open on each cylinder, and that's why there's no compression."

I considered that too but due to his description of crankshaft spinning sounded like no friction of pistons moving.

Walt Conner

AYP123

Discussion Starter · #8 · Jul 28, 2019

RedOctobyr said:
I have a Briggs opposed twin, but fortunately haven't needed to dig into the lower end! From the pic that Cannon51 posted, it looks like the near-side connecting rod bolts (at the crankshaft) are accessible. If you could also reach around the crankshaft to the far-side rod bolts, then perhaps you could undo the connecting rods, and remove the pistons, with the cylinder heads off?

Before diving into the guts, I'd do the quick check to see whether the pistons are moving. As Walt said, it seems odd for both connecting rods to go at the same time, though if they are broken, it's lucky that nothing punched a hole in the block.

It's possible (albeit maybe unlikely) that a valve(s) is stuck open on each cylinder, and that's why there's no compression. It's easy enough to check for piston movement, and would tell you more about what you're up against.

I decided to dive into the engine today. So it looks like the top piston rod is blown. However, the piston can be moved and is not seized. I looked at the other side and it is fine however neither side has the valves moving. They are on the same position on both sides and do not move. That was from checking the heads on either side. I then took the rear cover off to find chunks of rod material all over the rear. There was so much, I couldn’t even get some of it out. It was bad. I don’t know if the rod blowing damaged the cam and caused the valves not to move but I’d have to take the pan off to find that. Also, the crank has a bit of rod material on it, but I think if I remember correctly that hydrochloric acid can remove that? Or do I need to take it to a machine shop. I can get pics, but I’ll have to pull the engine off first. The inspection I did was with the engine on the chassis. What are your opinions? Any ideas on why the valves won’t move? Do you think the old piston can still be used? Trying to figure out what parts I should order if I should get them.

RoyM

· #9 · Jul 29, 2019

The camshaft is likely broken. You will need to tear it down completely to clear out all the debris and assess the damage. Once the crankshaft is cleaned up measure it with a micrometer todetermine whether it is still within specs, if the journal is scored or shows evidence of wear then it will need to be ground if you can find a shop to do it. I don't know if p/n 498541 .020 undersize connecting rod is still available though.
The pistons may be reusable if not damaged or badly worn but it will depend on whether the cylinders are worn beyond limits.

AYP123

Discussion Starter · #10 · Jul 29, 2019

RoyM said:
The camshaft is likely broken. You will need to tear it down completely to clear out all the debris and assess the damage. Once the crankshaft is cleaned up measure it with a micrometer todetermine whether it is still within specs, if the journal is scored or shows evidence of wear then it will need to be ground if you can find a shop to do it. I don't know if p/n 498541 .020 undersize connecting rod is still available though.
The pistons may be reusable if not damaged or badly worn but it will depend on whether the cylinders are worn beyond limits.

Ok then. I’ll have to see how bad it is by tearing it apart. I’m hoping I don’t have too much to replace.

tomw0

· #11 · Jul 29, 2019

I think you want muriatic acid. I don't know if that is HCl type... chemistry was decades ago.
If you read about it on site, all recommend to use in a well ventilated area. OUTSIDE. Be prepared to throw away the clothes you are wearing as most are as clumsy as me when applying liquid, and will either splash or dribble. Not where I wanted it.
The acid should remove the Aluminum(connecting rod material that has transferred) so you can check for damage and measure.
Be prepared with a mixture of baking soda and water to neutralize any acid that gets where you don't want it. Might not hurt to have a bucket of water handy for quick flushing. And, hopefully all those precautions are wasted time...
tom

Walt 2002

· #12 · Jul 29, 2019

tomw0 said:
I think you want muriatic acid. I don't know if that is HCl type... chemistry was decades ago.
If you read about it on site, all recommend to use in a well ventilated area. OUTSIDE. Be prepared to throw away the clothes you are wearing as most are as clumsy as me when applying liquid, and will either splash or dribble. Not where I wanted it.
The acid should remove the Aluminum(connecting rod material that has transferred) so you can check for damage and measure.
Be prepared with a mixture of baking soda and water to neutralize any acid that gets where you don't want it. Might not hurt to have a bucket of water handy for quick flushing. And, hopefully all those precautions are wasted time...
tom

Good advice above. I prefer to have the wind blowing from the side. Natural impulse is to have wind to your back. This will cause a "Back flow" of air into your face. I wrap narrow strip of paper towel around the rod throw and dribble muriatic acid on paper towel. This will hold acid in contact with material longer. After a couple of applications, I flush with water, dry, repeat if aluminum not completely removed then cut a long strip of 600 wet/dry paper, back it up with masking tape, hold crankshaft in vise and whip/saw paper back and forth evenly all the way around using cutting oil . I have done this to many engines over the years. I once specialized in saving these engines. IF crankshaft throw is scored then repair is questionable depending on how badly.

Walt Conner

TobyU

· #13 · Aug 3, 2019

I don't find repairing engines to be cost effective unless you have years of used parts laying around.
If you give me a blown one, the price I have to pay to get a rod, gasket(s) and maybe crank or work done to it...is more than I can buy used often running good engine for.
You can mount about any engine on the machine and I would rather have a V-twin over a horizontally opposed twin. I would rather have a single briggs ohv on a lt 1000 with 42 inch deck.
We don't need over 17-20.5 hp to spin a 42 inch deck. People get hp-itis and spend more for a higher hp engine when it is not needed if they are all 42 inch cuts.
I will admit an 18 horizontal (or v even) twin will not bog down in tall grass like a 17, 18, or even 19 single will BUT if you trounce on through grass that tall without slowing down you will have a terrible quality of cut and have to go back over it anyway.

On new mowers people often buy the bigger vtwin "upgrade" and almost always they have more trouble with it than they would have had with a single in the years of ownership.
More coils to fail, valve rocker studs to looses up, pushrods to bend or jump off (and even ingest on v-twins), vavle guides to slip.....

38racing

· #14 · Aug 3, 2019

TobyU said:
I don't find repairing engines to be cost effective unless you have years of used parts laying around.
If you give me a blown one, the price I have to pay to get a rod, gasket(s) and maybe crank or work done to it...is more than I can buy used often running good engine for.
You can mount about any engine on the machine and I would rather have a V-twin over a horizontally opposed twin. I would rather have a single briggs ohv on a lt 1000 with 42 inch deck.
We don't need over 17-20.5 hp to spin a 42 inch deck. People get hp-itis and spend more for a higher hp engine when it is not needed if they are all 42 inch cuts.
I will admit an 18 horizontal (or v even) twin will not bog down in tall grass like a 17, 18, or even 19 single will BUT if you trounce on through grass that tall without slowing down you will have a terrible quality of cut and have to go back over it anyway.

On new mowers people often buy the bigger vtwin "upgrade" and almost always they have more trouble with it than they would have had with a single in the years of ownership.
More coils to fail, valve rocker studs to looses up, pushrods to bend or jump off (and even ingest on v-twins), vavle guides to slip.....

I'm in the hp bit now. I was given a fire damaged 50" zt50. Engine is Tecumseh vtwin with dual carbs. After finally getting it running on both cylinders I blew a head gasket. Just getting it back together. I have an 18 hp single I could put on it or maybe an old opposed twin (fit?). I figure I once ran a 42 deck with 13 hp why can't 18 handle the extra 8 inches. I could always cut a bit narrower and stay out of heavy cutting. Even 8 hp will run a 30 inch deck.

Walt 2002

· #15 · Aug 3, 2019

Believe it or not, the standard Dixon 42" 1977~1980s ZTR was an 8 hp B&S. Deluxe model was 11 hp B&S. 11 hp did a good job.

Walt Conner

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green dream machine

· #16 · Nov 21, 2019

didn't those engines have a plastic cam gear?

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