# Craftsman lost compression



## tblitz (Jan 29, 2011)

I just picked up a Craftsman 5hp 24" model# 247.886640
This blower is in very nice shape, but it seems there is very little compression. Any ideas? Should I start tearing the motor down? Any one else ever have this happen? Any help would be great.


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## HCBPH (Mar 8, 2011)

*Compression*

If it was mine, first thing I'd look for is either heavily carboned valves or a stuck valve. After that, maybe a bad head gasket (might check this earlier), then I'd think rings.

I've had 4 Tecumseh motors I've worked on this year I bought used (snowblowers I bought for my own use), a 4, 5, 7 & 10 hp (the 10 is currently in progress). Personally I like to pull the head to check out the cylinder wall and tightness of the piston in the cylinder. In each case, the valves were heavily carboned up while the piston and rings seemed fine. I know some will say don't, but I take the engine (I pull the carb and muffler), rotate till one value is open then spray the valve & seat down with brake cleaner. I clean off what I can with a clean rag. Once the majority is off, I spray it down again then use a round brass wire brush in a drill on low speed and go around the underside of the valve and seat cleaning off all the carbon I can (don't use a steel one, make sure you have a real brass one so it won't scratch the steel). Clean up the excess, rotate it so the other valve is open then do that one. Once that's done, clean up the junk including any wires that came off, clean it all up. I then rotate it so the piston is in the down position and wipe the cylinder walls and piston top with light oil. I like to leave it overnight to air out well then put it back together. While the block is airing out, you can decarbon the head if need be.

The 4 & 7 feel like they picked up some compression based on rope pull (the 4 also had a bad head gasket), 5 didn't seem to have any difference and I am in the middle of the 10 so don't know yet. 

Nice thing with pulling the head is you can also check a number of other things.

My 2 cents


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## tblitz (Jan 29, 2011)

Hey HCBPH I may try to pull the head this weekend to take a look at the valves. Never heard of using brake cleaner on valves. Don't they make something to clean them? I hope maybe a new gasket and valve cleaning is all it takes to get it going.


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## Shryp (Jan 1, 2011)

I have seen quite a few posts on various forums about 5HP Tecumseh engines on snowblowers loosing compression. The fix is almost always the exhaust valve needs to be ground down and lapped.


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## HCBPH (Mar 8, 2011)

*Brake Cleaner*



tblitz said:


> Hey HCBPH I may try to pull the head this weekend to take a look at the valves. Never heard of using brake cleaner on valves. Don't they make something to clean them? I hope maybe a new gasket and valve cleaning is all it takes to get it going.


I also was amazed at how well brake cleaner works. I tried carb cleaner on one old engine and it wasn't making any progress on the carbon. I happened to have some brake cleaner handy so I tried it. It was amazing how it took the carbon off the top of the valve and head, just spray and started seeing bare metal in some areas then wipe up what you can. Happened to have a fine brass brush for welding on hand so combined the two and it came up clean, including the valve seat without disassembling. I've found round ones for a dremel tool at Home Depot, and a larger one at Fleet Farm to use in a drill. 

I try to do it with the piston as close to TDC as possible so little if any gets in the cylinder. I realize it can wash the oil off the cylinder walls, that's why once it's all cleaned up I wipe down the piston top and cylinder walls with light oil before reassembly. In each case, this was done on a non-running motor, once I had it going again, I'd change the oil. Probably not necessary but for what a quart of oil costs, it's worth the peace-of-mind to do it.

Don't get me wrong, nothing wrong with grinding the valve and lapping the seat, but if all the problem is is carbon buildup and it can be removed without disassembly, it seems like something that could be tried first. It's worked for me, so try it if it seems reasonable to you. Your mileage may differ - lawyer stuff, just cause it worked for me doesn't mean that's your problem or it will work for you.

Good luck.


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## tblitz (Jan 29, 2011)

Thanks for all the info. Does anyone know what the compression reading should be on the 5hp Tecumseh motor it has? Also what would be the max rpm this motor should run?


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## Shryp (Jan 1, 2011)

Max RPM should be 3600.

Compression will be hard to tell because the compression release won't let it read above 50-60 psi.


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## tblitz (Jan 29, 2011)

Shryp said:


> Max RPM should be 3600.
> 
> Compression will be hard to tell because the compression release won't let it read above 50-60 psi.


 I didn't know it a compression release. Is that why it pulls so easy? You sure it's got a release on it?


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## CarlB (Jan 2, 2011)

Shryp said:


> I have seen quite a few posts on various forums about 5HP Tecumseh engines on snowblowers loosing compression. The fix is almost always the exhaust valve needs to be ground down and lapped.


 +1 on that. I had to grind the valve stems on 3 5hp tec's this year to get the proper valve lash.


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## Shryp (Jan 1, 2011)

tblitz said:


> I didn't know it a compression release. Is that why it pulls so easy? You sure it's got a release on it?


They have a small bump and spring on the camshaft that keeps the valves open slightly until it is at speed. That is why the engines are so easy to pull start.


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## tblitz (Jan 29, 2011)

Do you know if this model takes two belts that are the same? I know the drive belt takes # 754.0343, is auger belt the same? Plan on changing both soon. Is it hard to do?


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## ss195 (Dec 29, 2016)

Just finished fixing a HSSK50 Tecumseh with low compression. Was on an Ariens 524. Picked it up cheap as it started on electric and only ran on high speed but didn't sound right. The guy "broke" the starter cord so I couldn't tell it has low compression until I got it home and started to work on it. I see he also had the idle screw all the way in trying to mask it. 

Anyway, I was suspicious of the exhaust valve because of the "puffy" way it sounded when it ran. Cold compression way low at 59psi so I pulled the head and check the exhaust valve on compression stroke. It was "loose" and easily turned indicating it was not closing all the way. Piston/walls looked great. Usual amount of carbon - no issues. Pulled the exhaust valve and the seat was corroded indicating it was not closing. Must have not been run too long as there was no seat burning. I took .015 off the stem length, lapped it with compound until a clear pattern was evident, and re-assembled everything. It now has 120psi cold and runs perfect at all speeds.

Apparently there must be a design issue with these engines. This is the 3rd one I've had with the same problem. Ironically, I have a 1961 tecumseh that still runs flawlessly! It seems the later ones (not sure of specific years) seem to have the valve issue.


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## detdrbuzzard (Jan 20, 2012)

hello ss195, welcome to *SBF,* nice work


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