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Workshop => Engine and Bottom End => Topic started by: Bigred on July 26, 2013, 12:45:41 AM

Title: Compression ?
Post by: Bigred on July 26, 2013, 12:45:41 AM
Ok it's a spacer plate motor new ring and piston and bore and has a cool head with pump gas dome.  Did a compression check (yes gauge is good and accurate) it blew 150. Now I have paper gaskets on top and bottom of spacer plate. I have a cr gasket under the cool head it's a 3 piece.  Do I undo the 3 piece gasket and use one to bump it up or is there another way.    Also I only had the head pipe mounted not the whole exhaust will that make a difference. Thanks or any and all input
Title: Compression ?
Post by: Polonda on July 26, 2013, 01:00:05 AM
You need to at least check your squish with some solder.  Changing gasket thickness at the base will change port timings some.  At the head will not.  Both will change your squish.  Get a squish measurement for us then we can make some recommendations based of what type of gas you want to run.  Best way is to do a UCCR and squish test.
Title: Compression ?
Post by: Bigred on July 26, 2013, 01:06:40 AM
Ok got a sticky on how to find the squish?  It's a trail rider 93 is all she gets. Just want 180-190 compression
Title: Compression ?
Post by: Bigred on July 26, 2013, 01:09:41 AM
Nm I found it
Title: Compression ?
Post by: F-Red on July 26, 2013, 06:51:46 AM
Quote from: Bigred;5774
Did a compression check (yes gauge is good and accurate) it blew 150.


Has the motor been broke in? A fresh unfired motor, typically will have 20-30psi less than a broke in motor.
Title: Compression ?
Post by: jcs003 on July 26, 2013, 07:13:49 AM
what kind of compression gauge?  some adapters dont go as deep as the spark plug and will throw off you readings.

also, as F-Red stated, if the rings arent seated yet the compression will be lower.

john
Title: Compression ?
Post by: Bigred on July 26, 2013, 09:00:46 AM
Motor never been fired yet. Not sure if my jetting is even close to have it fire lol. Gauge is a good one my buddie is a mechanic. Says its within 1 psi accuracy . Ill have to get it all buttoned up and try to get it to fire. Do some heat cycles then check it again thanks for the advice
Title: Compression ?
Post by: trx88 on July 26, 2013, 09:31:01 AM
Quote from: F-Red;5793
Has the motor been broke in? A fresh unfired motor, typically will have 20-30psi less than a broke in motor.

there were times i wish i had known that..
Title: Compression ?
Post by: F-Red on July 26, 2013, 09:51:01 AM
Quote from: trx88;5817
there were times i wish i had known that..


Me also! Some of us are monetarily taught! :greedy_dollars:
Title: Compression ?
Post by: F-Red on July 26, 2013, 09:53:30 AM
Quote from: Bigred;5809
Motor never been fired yet. Not sure if my jetting is even close to have it fire lol. Gauge is a good one my buddie is a mechanic. Says its within 1 psi accuracy . Ill have to get it all buttoned up and try to get it to fire. Do some heat cycles then check it again thanks for the advice


Set the jetting rich. Work it from there.


Quote from: trx88;5817
there were times i wish i had known that..


Me also! Some of us are monetarily taught! :greedy_dollars:
Title: Compression ?
Post by: Rupp250 on July 26, 2013, 09:59:31 AM
Like stated, measure UCCR and squish.  I don't use a compression gauge to tell me how to set up a motor. I use my builder for that.

I do use a compression gauge to monitor engine health.  And the one I use is off, but it reads the same consistantly though. If you read the gauge then went to kick it over, you would be like huh?
Title: Compression ?
Post by: Bigred on July 26, 2013, 10:38:06 AM
Bought my carb off .net few years ago its setup for a 400 plonda so im sure it will be rich already
Title: Compression ?
Post by: Rupp250 on July 26, 2013, 10:56:21 AM
Pull it apart and let us know what jets and needle are in it. Should be able to tell you where to start at.

At the same time it would be good to make sure it is all clean.
Title: Compression ?
Post by: Polonda on July 26, 2013, 01:23:59 PM
Big motors can actually use smaller jets sometimes due to the piston having a bigger pull on the jet.  Better open it up and check that out like stated above.
Title: Compression ?
Post by: Bigred on July 26, 2013, 11:30:15 PM
Ok will get the numbers tomorrow carbs clean went thro it when I got it then went into a plastic bag
Title: Compression ?
Post by: Bigred on July 27, 2013, 09:59:54 PM
Ok here are numbers needle is a DG J 3rd clip down looks like 188 for a main 48 for the pilot
Title: Compression ?
Post by: Bigred on July 27, 2013, 10:04:26 PM
Another question swing arm nut I know it's a 14mm but what's the tread pitch if anyone knows
Title: Compression ?
Post by: F-Red on July 28, 2013, 09:01:35 AM
Quote from: Bigred;6123
Ok here are numbers needle is a DG J 3rd clip down looks like 188 for a main 48 for the pilot

That's not a bad starting point. Fire it up, get some heat cycles in her.

Quote from: Bigred;6124
Another question swing arm nut I know it's a 14mm but what's the tread pitch if anyone knows

1.5 pitch.
Title: Compression ?
Post by: Bigred on July 28, 2013, 01:19:51 PM
Ok sweet thanks