160lb compression on my EC 300

[FFRDave]

I just rebuilt it a little over a week ago, and did a real gentle break in. I took it for a ride with a 180 main and a 42(if I recall right) pilot. I think these were too lean, based on info found here. During this ride, it did just shut off, but I got it restarted and was able to ride the rest of the day with no further problems.

Since then, I have gone to a 185 main and a 45 pilot.

I just got her all warmed up and was able to get 160 lb compression on three different tries kicking it 3 or 4 times on each try.

I took the seat off, and all three of the bolts, and the rubber-band holding the tank on.
Then I started it and let er' warm up for a few min. I then (while still running) disconnected the fuel line from the carb and removed the tank.
Then I shut it off and removed the plug for the compression check.

I think 160 is a pretty good number since I havent even sent my head to RBD for squishband adjustment. I will look for a decline in this number to tell me if my sudden engine stoppage was due to a minor seizure, or just crap in my carb.

[widebear]

The correct method. Engine warm, throttle wide open. you should get higher #'s this way.

[GMP]

You also have to kick more than 3 or 4 times, kick till the guage peaks.

[FFRDave]

I kicked until the gauge peaked.

It only took three or four kicks to peak the gauge with the therottle wide open.

I did all of this after warming the motor just as everyone suggests.

What numbers SHOULD I see????

I thought 160 was pretty good.

[iancp5]

Originally Posted by FFRDave

What numbers SHOULD I see????

I would guess you should see 160 if it's just rebuilt!
Personally I wouldn't lose sleep over the compression if it's running well. You would probably see a different reading on a different guage unless you have invested in some expensive high precision item.

[FFRDave]

I have read on here (this sight) that Gassers tend to run a little low on compression due to the conservative squish-band clearences in the combustion chamber.
This can be improved with the RB Designs head mod., therby ncreasing compression and improving fuel efficiancy and overall horsepower.

Considering that the stock Gasser head is known to give lower compression numbers, 160 seems pretty good (as I said before).

I am not using an $800.00 Snap-On, or Mac Tools compression tester. Mine was somewhat less than $100.00, but it should be good enough for what I am doing and how often I do it.

Widebear and GMP each seem to have some conserns about my testing methods. Perhaps they expect HIGHER numbers like 180, 190, or even
200. They may be assuming that if I used the correct method, I would be getting those 180 to 200 lb. compression numbers.
Assuming that 190 or 200 are the right numbers and 160 is way too low (indicating a problem), and I have used good testing technique. I better tear it down and have my cylinder re nickel sealed.
Decisions are being made based on the opinions of people I am in contact with here on this sight. These decisions have financial impact and are not taken lightly. Ultimatly, I am responsable for each decion I make, nomatter what its based on.

If someone comes on here and tells me that 165lb compression is my target, I will be happy with the 160 lb I got. If 190 or 200 is my target, then I will be more concerned.

For a freshly replaced, brand new 300cc cylinder and head, without RBD head mod., using proper testing technique as noted above, what is the expected range of compression readings?

Is 160 Lb. within that range?

[PEB]

When you say "during the ride it did just shut off" are you saying it stalled or arew you saying it siezed? If it siezed then tear it down, if it stalled no big deal. Have your compression tester tested before you run out and tear the bike down. I would use the 160 number as a baseline. If the bike is runniing nice and tight with lots of snap who cares what some number says. If your bore looked good when you put it back on surely it didn't go bad when you assembled the bike. Sometimes I think a guy can gather to much info from these sites and worry about everything that has gone wrong on someone elses bike. The best way to know if you got it right is to put a couple hundred hours on it this year and tear it down again next winter.

Paul B

[FFRDave]

I apologize in advance for the loooooooong story.

A couple months ago, I decided it was time to rebuilt the top end on my GG EC 250. It was running fine, but I just figured IT WAS TIME.

I will spare you the details (the long part of the story). After the rebuild, I did everything I knew to break it in correctly. Then I lent it to my friend and he called me to rescue him. The cylinder was a complete disaster !!

I began to investigate the cause and thought I had found the two forward nuts looser than they should have been (not fully torqued). I was relieved that my friend had not been at fault.

I spent over a thousand dollars at GoFasters on a whole new cylinder, head and misc. other parts and resolved to get it back to gether. This was a cc upgrade fron a 250 to a 300.

I got it all back together and heat cycled it twice. By heat cycle, I mean that I started it with the choke on and just warmed it up and then shut it off to fully cool. I did this on a wendsday night and then 24 hours later on a thursday night. On friday, I went for a short mellow ride in the flood plane behind my house and put it away.
On Saturday, I took it out to a local riding area for a bigger ride. The temp was hovering around freezing (probably 30 to 40 deg F). This was with no jetting changes from summertime riding (180 main and 42 pilot and an LTR needle in the center clip position).
After about an hour or so of really nild riding, I stepped it up a notch and went for mid range RPM for a half hour or so. By this time I was feeling like the break in was sucessful, so I found my favorite sandy beach and cracked 'er wide open and let fly what may. AMAZING !!! That 300 had SO much power !!! .... And then... she wound to a hault

I did get it re-started, but only ran for a second or two. Then on the second attempt she ran OK. The rest of the day, I was afraid to open 'er up like I had before, but we had a good ride at mid and low RPM.

Then I read about jetting for cold weather.

I installed a 185 main and a 45 pilot jet last week.

My concern is that I may have had it jetted way too lean all this time and I was repeating exactly what my friend had done when it seized on him last month. Maybe those cylinder base nuts were OK and maybe they were not, but it could have been the jetting all this time.

Now I am looking at my compression to tell me if I am having problems.

I am afraid that my mellow riding style (as opposed to my friends ALL OUT FULL GAS ON style) may be hiding a partialy seized engine. The bike seems to be running fine and I have 160 lb. of compression.

How much compression should a healthy 300cc Gas gas EC have?

[PEB]

It only costs a couple bucks in gaskets and beer to take a look see at the inards of the top end.

Paul

[GMP]

Ping Ron at RBD, I'm sure he has a lot of data from various 300s he has done heads on. Depending on gaskets, the 250s are from 185 - 195 PSI, so I would expect the 300s a little less. I know the KTMs run around 175 PSI.