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Dispro compession

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mcinton
New member
Username: mcinton

Post Number: 1
Registered: 08-2010
Posted on Saturday, August 14, 2010 - 01:22 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

What should the compression be of one cylinder Dispro engine with good seals and new rings.Can a compression tester be used on a Dispro Engine?
Thanks for any help anyone can give
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doug11k
Senior Member
Username: doug11k

Post Number: 72
Registered: 12-2003
Posted on Saturday, August 14, 2010 - 09:15 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

mcintom,
Without putting too fine a point on it, give flywheels a quick flip .... if they bounce backwards against compression you have enough compression and engine is free enough to start. If flywheel rolls thru TDC you have a compression problem. If they hang up near TDC engine may be too tight to start.
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miro
Senior Member
Username: miro

Post Number: 482
Registered: 11-2001


Posted on Monday, August 16, 2010 - 10:17 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

The compression ratio for the Dispro is about 4.5 to 5 :1.
That means you'll see about 60-70 psi on the compression tester.
But they'll run will leaky or worn rings any way, assuming all the other stuff is OK.
Since they are a 3 port engine , the crankcase seal should be good, i.e. give the grease cups a good twist.

The most important this to get them to run is good spark ignition. As I've said before - about 80% of carb problems are electrical.

miro
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ernie
Senior Member
Username: ernie

Post Number: 1248
Registered: 01-2002


Posted on Monday, August 16, 2010 - 11:23 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

More and More I am seeing fuel to oil ratio causing compression problems.
A friend asked me to come look at his St L as the compression was low. He had the piston out and all looked ok so I put it back in. The compression was ok. Then I noticed he was running it on 40 to 1 gas to oil. So we ran it and lo and behold after running it for a while the compression was real poor. Just barely a bounce. Squirted some oil in the cylinder and then ran it on 16 to 1. No more compression problems. Yes the engine has some wear but not enough to put in new rings.
Hope this helps
Ernie

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