12 HP B&S cam timing, Engine re-build

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  #1  
Old 05-18-07, 03:47 PM
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12 HP B&S cam timing, Engine re-build

1) I took my 12 Hp engine apart and took care to notice the Camshaft timing marks but since the crankshaft is small in diameter than the Camshaft gear when do you line up the dots? I think when the piston is at TDC. Please advise.

2) Could I get way with only honing and replacing the piston and rings without touching the valves? The valves look good but just need a cleaning.

3) There is some minor scratches on the cylinder walls (aluminum pistons scraps) and I was going to remove some of it with Miraic acid and then hone it and replace the piston and rings.

4) Does anyone have a PDF of engine schematic or rebuild instruction manual? The engine is a B&S Model #281707 0116-01

I have rebuilt many 2 strokes and this is my first 4 Stroke and do not want to pull the engine apart again but also don't want to go broke re-building it.

Thanks
 
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Old 05-19-07, 01:19 AM
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1) just line up the marks. It's the same every time.

2) You could if the valves were in spec, had the correct clearance, guides are good, and seats and mating areas are good.

3) If there are scratches that are more than what will come out with a little honing, then you have problems. This engine may not be a candidate for a re-ring job. You need to measure the bore to see if it's in spec, and cut the ridge at the top of the cylinder. It may need boring.

Another thing to look at is the balancer bearing surfaces. These gets pretty worn, especially at the top end. This causes a knock, and I've seen some of these come apart and blow the engine. The bearings are not replaceable...you have to replace the entire balancer. Sometimes the crankshaft journal that the worn balancer bearings ride on is also worn, and requires replacement. This exceeds the value of the engine.
 
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Old 05-19-07, 03:46 AM
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My motto is and always will be, "Do it once and do it right". If you're going to do a ring job, why not take care of the valves? Also, double check your engine ID numbers, the 0116 type number does not show as valid with a 281707 model. Do you have the Briggs service manual for your series engine? Which would give you all the specs you need to do the job right...Bore, ring end-gap, crank specs, rod specs, valve specs, bearing specs and so on and so forth.
 
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Old 05-19-07, 05:53 AM
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Smile

I do not have the service manual but did find some specs off the web. I have been looking for a service manual so I can do more on the engine. If you know where I can get a service manual in PDF format that would help.

I bought the riding mower for 250$C and don't want to spend much more than that on repairs cause I don't think it's worth more than 500 if in excellent running condition.

I will see if a local shop can do the valve job and check the piston and cylinder to see if a bore job is needed. I would like to do most of the job myself but buying special tools for a one time re-built is not worth it.

What do you guys use to clean the carbon of the cylinder head and valves>?

Thanks for all your help.

Cheers
 
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Old 05-19-07, 09:49 AM
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Course-grit Roloc discs used on a 2" die grinder and 120-grit emery cloth for the valve faces.
 
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