Author Topic: M91 #2 Repaired & Modified to Run Slower with Lower Compression & Softer Springs  (Read 107 times)

RedRyder

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You may recall this one had a slightly bent crank shaft and the pushrod assembly had been stuffed a bit in shipment. Jin sent me some new parts for it.

While I had it apart to make the repairs, I put the piston in my lathe and shaved 100 thousandths (.100) off the top to lower the compression.

I was a little concerned I may be taking too much off it but the result is quite pleasing.

I had already replaced the stock governor springs with considerably softer replacements. Then went the extra step and disconnected one of them. With the higher compression it would only fire once and then slow down so much it would bounce off compression and stop altogether. Now it runs much more gently and a fair bit slower as well.

While it was apart I took the opportunity to polish the radiator, tank, pipes, pump, and a bit more to dress it up a little.

Below are a video followed by some pictures.

Enjoy,

Gil


https://youtu.be/qM7bqDkZZeo


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Nick

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Nice improvements Gil!
Nick

St Paul Steam

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Also agree with the nice improvements , she looks like a new Penny now & runs really smooth,  nice work Gil.
Bruce
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Stoker

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A couple of questions Gil.

That does seem to be a whole lot off the top of the piston, but one thing I've considered doing with my M90 is to C'bore & cone the spark plug hole in the head so the spark isn't lost in such a deep hole, but rather has better "access" to the compression chamber, which would also lower the compression by increasing the volume. However, proximity to the valve seats would be the limiting factor, and would not really allow much of a bore increase nor chamfer, thus not much decrease in compression. What do you think about that approach?

The softer springs from the motor brushes seem to be helping too. Do you recall which specific motor or tool those brushes are supposedly made for, as my local Ace only seems to list them as replacements for specific brands of power tools.

That polish job really makes the radiator jump out .... making the whole engine more eye-catching!

Seems to jump around a bit less now too!?!?
"Information is not knowledge, Knowledge is not wisdom, Wisdom is not truth, Truth is not beauty, Beauty is not love, Love is not music: Music is THE BEST...   
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RedRyder

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Thanks, gents.

Daniel, I have no idea what these brushes will fit. I was shown the drawer that housed them all and I simply chose the two smallest sizes they had, both of which had the same spring.


It does jump around a lot less.


There are long threaded 1/4-32 spark plugs available that will solve most of what you are looking for re putting the plug more into the line of fire (fuel/air). I can't help but wonder if having the plug tucked up in there so far is helping, hurting or not mattering regarding fowling?
Power isn't an issue as this is no racing hemi!



crazydoug

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Gil,
Does the piston wrist pin just push out or are there screws holding it in from the underside of the piston. Think i will do this to lower the compression as well. Thanks for taking the "risk" for us!
crazydoug

krypto31337

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That engine is looking really pretty!
My Workshop Blog:  http://doug.sdf.org/

IndianaRog

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Wow Gil...truly a thing of beauty and runs so much slower, smoother than stock.  I love the look of polished brass and I think I will put my Simichrome polish to work soon!  Nice!!!!!

Rog
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RedRyder

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Gil,
Does the piston wrist pin just push out or are there screws holding it in from the underside of the piston. Think i will do this to lower the compression as well. Thanks for taking the "risk" for us!
crazydoug


The wrist pin pushed out easily. On the horizontals I have some slide out easy and some seemed pressed in and would not move. Pressed or glued?

Dr.Rev.DelmarMacReady

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That looks spectacular polished up, Gil. I plan to eventually pull mine down to do the same. I'm off to the video section to see how she runs. Certainly looks a treat.
Bennydaheeb

 

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