Maytag 72D compression test?

[KeithW]

Hello all,
I just honed the cylinders and put new rings in my 72D. After about 2 hours of rich, no load break in I did another compression test. With the old rings they were about 50 PSI. With the new rings they went to 60 and 70. Could someone do a compression test and let me know what they find?
Thanks,
keith

[Andrew Mackey]

The 72 is a low comp ratio engine - about 5:1. 50 PSI compression is not unreasonable, the engine should run on it . 70 PSI? Sounds a little high. To break in rings, on a 2 stroke, regular oil mix - 16:1, on the Mayteg, start engine, warm up, load engine heavily for 2 minutes, adjusting the mixture for best power at loaded condition. Let idle to cool down, for 2 minutes, and repeat. Do this repeatedly, loading engine to slowing, near stall load, each time increasing loaded time by 30 seconds, until loaded time is at least 6 minutes. DO NOT STOP ENGINE BETWEEN LOADINGS! This should seat in your rings. A common problem with 2 strokes, is that the rings are overlubricated on break in. When this is done, the rings never seat properly, as the cylender gets glazed before the rings seat. Remember, the twin is not a high compression engine! You have to 'work' the engine to seat the rings. Check compressoin on both sides in the same manor: Engine cold, First remove both spark plugs. Make sure that the plugs or the wires are grounded. failure to ground both wires or pluge WILL damage your coil! Next, Open the choke cap 3 full turns. Then, install compression guage, and kick over engine at least 4 times, and note highest number. Repeat on second cylender. Your results should read both cylenders within 10% of each other - for example, if one cylender reads 50 psi, the other must read within + or - 5 PSI (45 to 55) At 60 -6 PSI differential, etc. If you have 70 psi on one and 60 on the other, you are outside the 10% limit (7 PSI), and the cause must be found (poor ring seat, heavy carbon in cyl, worn cylender - piston (are they in spec for clearance?) The compression test should be made cold. If you do it hot, the engine cools as you do the test, and the cooling will skew your test data!.
Andrew

[KeithW]

Well, sounds like I'm not too far off. What should the piston to wall clearance be? To do the compression test I spun the engine over with an electric drill. A bit faster than it can be kicked over and could explain the higher readings. I'm really not unhappy with how it is running it just seems to be low on power so I'm sorting through possible causes.

keith

[youngmaytagstud]

have you tried to adjust the gov. in your crankshaft. if not, one screw does nothing but one adjusts speed. tighting-increases speed. loosening decreases. just a thought.

[KeithW]

I have adjusted it. Right now it is set so it runs about 1300 unloaded then I load it down to around 1150. I suppose that the govener might be sticking. Although I can adjust the speed with it, it really does not seem to have much authority.

keith

[Andrew Mackey]

The Model 72 is rated at 5/8 HP! the 82 and 92 singles @ 3/4 HP. Spinning with a drill actually may lower compression as the governor may be closing the intake!, in any case, the compression pressure is not affected by speed, with an open throttle, the top pressure will remain the same.
Andrew

[John Ledbetter]

Now I know why my Mom had so much trouble with her washing machine. She forgot to check all these things Out.

[KeithW]

Well, I'm sure it will be like my little Datsun Roadster, once all the bugs are sorted it will work great for a long time. This engine was purchased as "complete". Actually a pile of mismatched parts. Caps didn't match rods and lots of other problems. It did seem to be leaking excessive oil around the kick starter side crank seal. I tore it back apart and discovered I had used the wrong size 0-ring and it was not sealing at all. This, of course, is a big issue with a two stroke. I'll get out and get the correct o-ring and hopefully my 1/8 HP will get closer to the 5/8 HP where it belongs.

keith

[Andrew Mackey]

The original seal was the bearing itself. A small amount of leakage was needed to allow oil to reach the entire bearing. check and see if there is play in the bearings. Clearance should be only 1.5 to 2 thousandths (.0015 - .002", any more than that, and you are going to lose a lot of internal pressure in the crankcase! This leads to ineffecient fuel-air transfer into the cylenders - less power. If play gets bad enough, the magnets in the flywheel will contact the magneto. Especially on the twins, bearings are critical.
Andrew

[KeithW]

Looks like I'll be picking up some bronze at the hardware store on Tuesday also. About .008" play in the shaft.

keith

[KeithW]

Well, installed a new bronze bushing and O-ring in the kick starter side of the crank. It no longer slings oil, runs a bit better and seems a little quieter. There might be 5/8 HP in there but I don't think it's going to come out. Calculated at the rings no doubt. In any case I'm pretty happy with it. Now on to the Hercules/Economy. maytag1

maytag2

keith