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no compression, still ran

A
Feb 23, 2014
12
0
1
Michigan
I have a '94 yamaha vmax 600, and it started backfiring like crazy out on the trails, but I was able to drive the 30 miles back to my cabin, but other than that it started no problem and ran pretty good. I was trying to find out was causing the back firing, finally tested the compression and it was at 0. Checked the cylinder and piston and they were both toast, the piston ring broke and destroyed the piston and the wall of the cylinder. Replaced it and it all ran great. But I was just wondering everything I read if you are under 90 compression or so it shouldnt run, or atleast start easy, yet my sled was starting first pull everytime and such, I was just wondering how was that possible?? was I just "lucky" or am I wrong and that is pretty normal? thanks!
 

bholmlate

Well-known member
Premium Member
Dec 3, 2009
1,400
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113
Reno, Nevada
I am guessing that the first reading was off. Either the gauge or the process. Did you check all the cylinders or just one? it may have had very low compression as well that the guage did not pick up on. But gas engines don't run without compression as far as i know.
 

sledheader

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Lifetime Membership
Feb 18, 2013
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Between a Rock and a Hard Place
I am guessing that the first reading was off. Either the gauge or the process. Did you check all the cylinders or just one? it may have had very low compression as well that the guage did not pick up on. But gas engines don't run without compression as far as i know.

The guage reading was off for some reason or another. As mentioned, without a lick of compression, it's physically impossible for an internal combustion engine to run.
 
A
Feb 23, 2014
12
0
1
Michigan
I am guessing that the first reading was off. Either the gauge or the process. Did you check all the cylinders or just one? it may have had very low compression as well that the guage did not pick up on. But gas engines don't run without compression as far as i know.

I tried multiple testers, also checked them on my other machine as well as other cylinder. they all tested relatively fine. I know it sounds crazy/impossible. Thats why I was asking on here. didnt seem possible.
 
S

snowmobiler

Well-known member
Nov 26, 2001
8,107
3,922
113
if the rings were broke maybe it was firing above the piston and firing below piston in the crankcase causing it to run good and have 0 compression.
 

bholmlate

Well-known member
Premium Member
Dec 3, 2009
1,400
778
113
Reno, Nevada
Snowmobiler
If the combustion of the gases in the cylinder expand and don't have anything to push against there is nothing that pushes the piston back down. therefore there would be no power and no torque on the crank.

you light a small amount of gas in a open container and you get a flash and fire. You llight the same amount of gas in a confined area and boom. My guess is that the Compression tester that you used was not calibrated to measure the amount of compression in the motor therefore it read zero. Once it was hooked up to something that had normal compression it worked fine. Sorry even at low compression you would noticed the loss in power. no compression no torque on crank and no drive. Not buying the fact it ran great and had no compression. just my opinion
 

retiredpop

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Lifetime Membership
Jul 3, 2001
1,349
295
83
Calgary
I have a '94 yamaha vmax 600, and it started backfiring like crazy out on the trails, but I was able to drive the 30 miles back to my cabin, but other than that it started no problem and ran pretty good. I was trying to find out was causing the back firing, finally tested the compression and it was at 0. Checked the cylinder and piston and they were both toast, the piston ring broke and destroyed the piston and the wall of the cylinder. Replaced it and it all ran great. But I was just wondering everything I read if you are under 90 compression or so it shouldnt run, or atleast start easy, yet my sled was starting first pull everytime and such, I was just wondering how was that possible?? was I just "lucky" or am I wrong and that is pretty normal? thanks!

A twin cylinder engine will run on one cylinder even if the piston is shot on the other side. I wouldn't exactly say they run pretty good but it is no mystery that it ran.
 
W
Mar 1, 2009
13
3
3
61
West Michigan
60 miles

Had a did'nt care drunk repair suppposibly mach. work on an 84 phaser,that forgot to put the rings on the pistons,,,,,,,,,, went 60 miles befor it desided to quite.............
 
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