compression relief valve??

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smoothcruiser

smoothcruiser

Member
Feb 16, 2011
35
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6
E. Haddam,CT
Hello, Mr. newbie here.I was just wondering if any of you shift kit riders out there ever tried anything like using a chain-saw type compression relief valve to aid in cold eng. starting? I just finished a 7 spd. cruiser build with the GT-5 Super-Rat and the SBP shifter kit. I've only put about 50 miles on her so far but it still takes some real effort on the pedal to turn her over.
 
wheelbender6

wheelbender6

Well-Known Member
Sep 4, 2008
4,059
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TX
There was a post where somebody found one on a moped parts site that fit China girls. I never heard how well it worked.
 
smoothcruiser

smoothcruiser

Member
Feb 16, 2011
35
0
6
E. Haddam,CT
Dear Jaguar,
Thanks for your reply.I'm not really sure what I might have done to the Super-Rat that makes it so hard to turn over. I did pull the jug and cyl. head when I got it to clean up some casting flash on the cooling fins and I did run the head over some #400 wet paper just to make sure she was true, but I really didn't plane the thing down. What would happen if I doubled-up on the head gaskets? Would that help? I'm already aware of the problem that exists with the poor quality crank and connecting rod bearings in these motors. I've already ordered another motor from gasbike.net that's gonna get real bearings and all stainless hardware for re-assembly. Any suggestions or tips you might have would be appreciated. thanks again.
 
V

vvomit

New Member
Jun 5, 2010
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earth
I had to lower the compression on my rat. I couldn't get the clutch tight enough to start it.
I was thinking of drilling the head and making a small spring loaded valve to bleed off some pressure. I think a small piece of brass would let enough out around the stem for starting.
 
B

bbamboo

New Member
Dec 24, 2010
10
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Pensacola ,Fl
vvomit,how did you lower the compression? My rat has 185lbs compression.It has two base gaskets on it already.I was thinking about two head gaskets or two thicker base gaskets.However the squish clearance measures about right and I am worried about it not running as strong if I raise the jug.How does yours run now?
 
Goat Herder

Goat Herder

Gutter Rider
Apr 28, 2008
6,237
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That's pretty kewl looking! that looks sharp.(^)

How much did it protrude in the combustion chamber. Not so much if it cleared everything but did it go flush in side per chance to keep the original Sqeash band?

Also its nice to finally have a picture of the Rat engine heads new factory sqeash band.
 
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smoothcruiser

smoothcruiser

Member
Feb 16, 2011
35
0
6
E. Haddam,CT
Minimal protrusion backed up compression ring on valve with two additional copper washers. Sorry about the wait in responding, not very good with sending pictures need sons help.
 

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Goat Herder

Goat Herder

Gutter Rider
Apr 28, 2008
6,237
20
38
N.M.
Wow now I want one it looks perfect! I have a J Shaft coming together that will be a highly modded China. Do you have a link to that valve please? I have never seen one on a small engine like that.
 
Goat Herder

Goat Herder

Gutter Rider
Apr 28, 2008
6,237
20
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Well the only thing that crosses my mind but only because I am not familiar with them is durability if they eventually don't seal right? I am imaging that's what they are designed for so they prolly work perfect! I am a life time bicycle peddler so I have no problem peddling into the J shaft for starting. Prolly gonna be taxing from compression and too hard on my designed mounting tho. . I have friends that won't be able to start this bike I am about to build.
 
skjjoe

skjjoe

Member
Mar 9, 2009
393
1
18
Boerne Texas
They have been used (and still are) used for years. I think that if you had one and it was properly installed you shouldn't have a problem.It would probably outlast your little engine.:) I am thinking about it myself to save a little wear on the bottom bracket and freewheel
 
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smoothcruiser

smoothcruiser

Member
Feb 16, 2011
35
0
6
E. Haddam,CT
I robbed it out of a junk Huskvarna chain saw mod. #359. It's the same one thats in my Stihl saw mod. #MS361. It's a ten dollar part at your local saw dealer. I also changed out the connecting-rod bearing with a German made one(INA bearing part # K10X14X13-TV) It's much better quality with 11 rollers in cage vs. only 9 in factory one. tossed the original in the crapper. also used only one base gasket under jug-that's all that was there when new. this motor has 9:1 compression right out of the box,why reduce it. sorry u had to wait for reply. m much better with wrenches than computer.
 
smoothcruiser

smoothcruiser

Member
Feb 16, 2011
35
0
6
E. Haddam,CT
hey, what's happening.I am assuming (hoping) that was the way China Gas shipped it out.The pits really stand out in the picture with carbon in them. There is less than fifty miles on the motor. That's how it looked when I took it off to install the compression relief valve. When my buddy (engine Andy) was milling out the cooling fins and seat for the valve install,there was poracity in the alum. up there too.I don't think it's gonna get any worse. It should be fine. At least the gasket surface was ok. I just hope they start making top end parts available soon for these rats. I'd like to have a spare piston,jug,and head on the shelf anyway just in case. I took her out today for a quick spin just to make sure everything went back together ok.(man,it's coooold out) She's runnin' strong and sweet. thanks for checking out the pics..shft.
 
smoothcruiser

smoothcruiser

Member
Feb 16, 2011
35
0
6
E. Haddam,CT
Not sure. this is my first build so I don't have anything to compare it to.It's got some good zip to it right out of the box.I havn't done any real mods to it yet except for gutting the catalyst out of the stock muffler and some porting on the stock intake.My buddy (engine Andy) and I both have rats on our first builds.He's running an expansion chamber exhaust and has also trimmed his piston skirt to match intake opening @TDC. He is very impressed with the results over stock.It's looking like I'm gonna be pulling my jug again to do some trimming on the piston skirt myself. what does ht stand for anyway? also do you have any pics of your stuff cause I'd interested to see?.wee.
 
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