CMB .45 Vac tear down

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Neil LaGarry

Well-Known Member
Joined
Mar 2, 2009
Messages
637
I’m adding new bearings. During the break down the crank came out of the case hard. Inside clearance between the two is close near the front bearing. I decided to lightly file the inside case. How if any oil get to the front bearing ? Doing that file job am I hurting performance?

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Im adding new bearings. During the break down the crank came out of the case hard. Inside clearance between the two is close near the front bearing. I decided to lightly file the inside case. How if any oil get to the front bearing ? Doing that file job am I hurting performance? IMG_1078.JPG

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The area between the two bearings is where the seal between the crankshaft and crankcase is made, usually.002 to .004 clearance between the crank and case. By filing it youve opened the clearance and it probably wont seal as good as it should. Engine might run but will lack low end torque and wont spook up.
 
We have found that the best place to put the front end seal is directly behind the front main bearing! This is because there is a bending force that takes place in the middle of any cantilevered type crankshaft. (FMV story, page 3) The remainder of the ID of the front housing is tapered to a larger size than the sealing area in the front housing. The width of the sealing area is approximately .2756" (7 mm) & the total clearance in .0001" to .0002". The crankshaft never touches when the seal is placed in this area! We have tested larger amounts of clearance ( up to .005") & the engine does run faster, 300 to 500 RPM, but there will be a considerable amount of oil seepage. There was no evidence of a loss at the low end or a decrease in the engines ability to pipe up when the larger amounts of clearance were tested.

Jim Allen
 
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It will be difficult to tune. I have a set of twin motors where the seal is worn out. Previous owner ran with bad bearing and ruin the seal. Only way I was able to tune those motors was using a sealed bearing on the front. Help to seal it up some. Still was not as good thou.

Mike
 
It will be difficult to tune. I have a set of twin motors where the seal is worn out. Previous owner ran with bad bearing and ruin the seal. Only way I was able to tune those motors was using a sealed bearing on the front. Help to seal it up some. Still was not as good thou.

Mike
Hi Mike If you added more castor oil to your fuel it would probably have had more affect to help the seal than sealed bearings.

Thanks John
 
I’m sure I filed off more than .0001 I could never go more than 1 plug per run. My squish was .012 on my head clearance. I only run one .45 nitro engine per race weekend. I have other engines to add. The Vac never woke up for me. Bearings was the last straw.
 
Bet it was toast from the start. The key to replacing bearings is not waiting too long or the situation you have becomes the result
 
It will be difficult to tune. I have a set of twin motors where the seal is worn out. Previous owner ran with bad bearing and ruin the seal. Only way I was able to tune those motors was using a sealed bearing on the front. Help to seal it up some. Still was not as good thou.

Mike
Hi MikeIf you added more castor oil to your fuel it would probably have had more affect to help the seal than sealed bearings.

Thanks John
Hey John

I was running 80-20 mix on my oil package. Klotz super techniplate. With a 20% oil mix. Still was trouble. Those motors were well worn and I retired them. No parts for rebuilds. So they just sit in the parts box. My other 2 motors are doing fine. I was able to get a new set of piston/head buttons for them this year from a friend. Need to rebuild them. One of these days I will finish the carbon twin and all this will be a mute point. LOL
 
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