Measuring the Cylinder

It is too cold so I brought the go-putz engine 28M707 and the 31P777 into the house.  Now that they have warmed up I am going to take another shot at measuring the cylinders.  In this post I will only be dealing with the 28M707.

Nominal bore is 3.440.  Used gauge block to verify and lock digital caliper at 3.440.  Setup bore dial indicator to zero at the caliper setting.  A real pain.  Then verified the virgin cylinder wall below the piston travel.   It may be faster to set the dial indicator on the virgin wall.  Not sure.

Checking the bottom of the bore verified the setting of zero as 3.44.  The wear along the axis of the crank travel is .012 over so we will need to bore this one to .020 over.

The bore below the piston is consistent as expected and will allow the hone to follow the center of the original bore.

Briggs 31P777-0237-G5

Bought a naked 31ci inch single cylinder BS engine today. 31P777-0237-G5.  I am seeing a lot of different HP figures for this engine so we will call it north of 15 and south of 20.   18 or 18.5 seems to be the the most common numbers.   Rumor has it that it has a cast iron bore.  18.5 is correct.

It is missing the starter and there is dirt in the filler tube which is missing the dip stick.  Need to figure out how to rinse the engine out.  I am not too worried with the pressure lube system. 

To the left is an image of a similar engine on ebay.

I should part it out but am tempted to get it running if possible.  One never knows why a 'found' engine is take out of service.

Starters from the old L-Head engines look like they might work.

The good news is that she is an oil burner and it has a cast iron sleeve!  It is too cold to inspect the bore.  The head gasket looked good.

Learned on the web that one can file the ends of of .010 rings and use them as .003 rings.  If it is out of round or tapered I will bore it out to .010 over and either get a rebuild kit or sell the block and bits on ebay.

Piston with rings is B&S 796173.  $87.52 with shipping from tewarehouse.

Service manual (missing images should be good one in repair books.
276781 Single Cylinder OHV .pdf

Cylinder bore inspection

To gain experiance with the dial bore gauge I decided to characterize the engines I have the heads off.

standard min 2.4990"   max 2.500"
Crankshaft is along the '2' axis

 dial reading     adjusted     

A1  -0.0005      2.5025
A2   0.0000      2.5030

B1  -0.0010      2.5020
B2   0.0000      2.5030                 

C1 -0.0015      2.5015            

C2 -0.0003      2.5027

2.4" anvil with .12" washer

Briggs says:

If the bore is more than .003” (.08 mm) oversize, or
.002” (.04 mm) out of round on cast iron cylinders, or
.003” (.06 mm) out of round on aluminum cylinders, it
must be resized, or see NOTE below.

The bore has reached but not exceeded the wear limit in the  '2' direction.

This is an aluminum cylinder so the larger out of round applies.   The worst level is level C at ( 2.5027" -2.5015 ")  or 0.0012".   This is not quite half of the allowed  003" allowed.

In the 2 direction we have a taper from bottom to top.   According to Oklahoma State "Taper in the top half is cause by dirt ingestion through the air filter. Taper in the bottom half is caused by dirty oil.

This is all based on trusting the digital micrometer I am using.  Would be nice to have some way to check it.

Lisle Cylinder Hone and Related tools.

Measuring GoPutz 's cylinder indicated that it needed to be sized up to .010 over. It took a long time to make the six measurements needed.  So I bought a Fowler Cylinder bore gage in addition to the Lisle boring hone. I also purchased #240   and #500  grit stone sets.   While I was at it I bought a better digital micrometer.

A boring hone should not be confused with a flex hone. The boring hone has the stones mounted solid to a rack and pinion arrangement that allows the hone to be precisely sized and expanded.

After reading the honing instructions I found out that I really needed a long reach micrometer to ensure the stones remain flat. 

My first idea was to hone the block in a tub of kerosene resting inside the parts washer.   Once I got it setup I found that there is a lot I did not like about it.

My plan B is to mount the hone in the drill press. This way I can set the speed using the belts and limit the stroke using the dept stop.  It does make recycling the kerosene harder  but that is a minor compared to what is gained.

To be continued....

Go-Putz has been started

The engine has been removed and torn down.  I have not removed the valves  which seem to be well seated.

The exhaust valve seemed a bit loose.

Found a plug gauge for briggs 5/16 valve guides on ebay for under  $10 with shipping.  It is NOS and a bit rusty in spots but should work.  Will use it to see if the exhaust valve guide on go-putz's briggs 13hp needs replacing.


Sunday, October 19, 2014

The plug gauge does not go in to the valve guide so it should be OK.
The plug gauge seemed large and I wondered if was the correct one but it is only .012 larger then the 5/16" specified for the valve stem diameter.

I measured the cylinder with snap gauges.  It seems every time I use these thing I need to relearn their proper use.  This motor looks to be well cared for. The insides are about the cleanest I have seen in an old briggs.    The cylinder out of round 0.0035 and taper 0.003 are not horrid but the larger dimension of the cylinder is too large for standard rings and both are too small for 10 over.

The cylinder needs to be honed to 10 over.   Looking at getting the Lisle LI15000 Engine Cylinder Hone.
    

Maybe a bit pricy for building a single engine  but  short of a cylinder boring machine it seems to be the only way to true up a cylinder.    

3Z107B 3 Cylinder SpeedAire Compressor (part 11) molasses update

I removed the parts from the molasses and cleaned them up.  The procedure was recorded with 2 cameras but there is a lot of video and  and it will take some time to edit it.

The parts were in the molasses for a long time and a crust formed along the top of the parts.  The good news is that it looks like there is no damage from this and a significant amount if not all of the buildup is gone from all but the worst cylinder.  The lesson here is to use a deeper container or rotate the parts every week or so.

The next step is to take the snap gauges and determine which cylinders to use.

Someplace on the web I read that a place which rebuilds compressors honed the cylinders by media blasting.  No details.  The idea is that it prepares the surface to better hold oil.

3Z107B 3 Cylinder SpeedAire Compressor (part 10) bearings

I had the bearings removed and replaced by a bearing shop.  The first step in putting it all back together.