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steamer

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What George said. She seems somewhat eager to go already!

Dave

 

vcutajar

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Sorry Pete if I am posting here but the subject just cropped up.

Forgive me if I am going to say something stupid (remember I am a newbie in i.c. model engines) but what does it mean when you say if compression feels good? Is there a magic number that it should be?

And another stupid question. Can an automotive compression tester be used to see if there is any compression?

Vince
 

steamer

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I'm sure George is a better judge of this than I, but if the will "bounce" on compression, your probably OK

I believe I read that George made a compression tester for one of his builds recently....maybe it's the radial...I'll look

No I don't believe a full size compression tester would be useful here as the internal volume of it would be very large....you would need a much smaller unit to really be useful with small cylinder I would think.

Dave

PS Didn't find it in the radial build.....Can't really remember where I saw it but it's around .....

 

Dave G

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Great job Pete. They always take a little tweaking but the first run is the best no matter how long it is. I've enjoyed this one alot. Thanks for sharing, Dave
 

gbritnell

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What Dave said is how I judge compression. When the engine is turned over if a definite resistance is felt when the piston is nearing top dead center then there's usually enough compression to start the engine. If it feels like what I call 'soft' when it gets to TDC then a person should start checking for the problem. I would say 90% of the time it's leaky valves. Over the past many years on this forum it seems the primary reason for 'soft' compression is from valve leakage as opposed to piston blow-by.
At one time I had made a miniature compression tester but with the very small displacements I don't know how accurate it was. There are some commercially made compression testers that won't even work on small engines, the lawnmower, weedeater type. The reason for this is because they don't have the check valve, that holds the compression, right at the tip of the adapter so when the engine is checked the amount of area in the hose has to be added to the volume of the cylinder thus reducing the compression pressure.
gbritnell
 

gbritnell

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Hi Mosey,
Why not take your comment and post it under the questions section that way this thread won't get too far off topic.
gbritnell
 

metalmad

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Well guys
The saga is not over yet ;D
Bez and Aus came over today and we got a couple of short runs out of her, but we all agreed there are carby problems.
As yet I'm flying blind here, but for the lack of anything better to do, I turned up a brass bush and pressed it in the throttle body taking the the venturi from .250 down to .190.
While I was at it I lengthend the cross slots which were not allowing full throttle.
Another weak area that came up was the throttle lever which kept slipping, so maybe ill pin it or something.
All in all, my take on the situation is this.
The Cam and Valves are good but the carby not so much. :big:
With any luck, ill try again in a day or so.
Pete

 

steamer

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Ah Sounds like normal teething.....great! You'll get it!

Dave
 

metalmad

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Looks like I was off the track a bit with the venturi bush, but I think I have it now. scratch.gif I had noticed that the wallaby would only fire when the mixture needle was basically falling out and today this led me to the discovery that I could only blow through the draw bar once the needle was almost taken out so after a bit of a rummage in the wife's sewing box I found a needle with a very blunt point and after soldering it in, I can now blow a little air threw it just cracked open.
Before tyring to start her again I want to remake the starting spigot out of silver steel and harden it but I think she will run now.
Pete
 

steamer

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Oh man.....start the thing will ya! ;D

Must be patient...must be patient...must be patient...........!


Dave
 

steamer

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Yo Pete! Where you at! Dropbar get ya? ;D

How's the patient?


Dave
 

metalmad

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Hi Dave
I pulled her down the other day chasing a very bad oil leak and after a full days work getting her back together found i'd mistimed the valve gear again, dame it. Which as im sure you will find out soon takes a good bit of time to take apart and put it back correctly.
And to make things worse it still leaks :big:
just at the moment it all seems like hard work ;D
Hi Bez
not so much beer time as Tax time at the moment :(
Pete
 

steamer

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Have you got the one way crankcase breather?

Whats leaking?

Dave
 

tel

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May be the XXXX Bar got him *beer* big laugh
I've heard that he's a XXXX man - up til then I didn't think anyone really drank it!
 

metalmad

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yup got the one way breather, I'm using some thin shim metal as the diaphragm at the momant but may go to rubber later if I need to.
I'm not sure whats leaking yet but it may be the banjo seal is not up to the task.
( A little plumbers tape on the fittings easily fixed the leaks )
One day Tel, I want to come down for the race over the Mountain and we will see then, what you keep in your fridge :big:
Pete
 

Maryak

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tel said:
I've heard that he's a XXXX man - up til then I didn't think anyone really drank it!
Gotta be better than Bulimba Gold Top.
 

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