160lb compression on my EC 300

F

FFRDave

New member
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.
 
YUP... Thats what I did

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.
 
FFRDave said:
What numbers SHOULD I see????
Click to expand...

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.
 
Numbers

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?
 
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
 
Thanks PEB

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:eek: !!

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:eek:

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

Paul
 
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.
 
I've been following this thread for a while to see if I could help out. I just went out and check my compression for shi$ts and giggles with the bike cold at 40deg. with the throttle wide open I got 170 psi. on my craftsman tester.
 
What would I be looking for ?

I could remove the head and run the piston to the bottom of its stroke and look for damage to the cylinder wall, or maybe alluminum deposited there. I could also take the pipe off and check the front of the piston.

Besides that, I really dont know what I would be looking for.

I really dont want to remove the cylinder again. I have F'd that part up so many times, that my confidence is just shot. Part of what is going on here is that I have had so much trouble, that I utterly lack confidence in my own work. PEB was right earlier when he told me to just go riding and I will know in a couple hundred hours.

I will continue to check the compression before each ride and look for a decline to tell me if I might be having trouble.
 
Last edited:
Dave, You can see alot with the pipe off, nearly the whole back part of the bore. If you are going to go to the trouble of taking the head off take the whole jug off. I hate to say it but if it siezed you should tear it down before something else happens. A replate or new piston is chump change compared with replacing bottom end parts. Besides now is the time of year to deal with this s%^t. It could run great for years or it could sieze on you again fourty miles from the truck this summer. Several summers ago my 02 ate a tranny deep in the Manastash system and the truck was near Cle-elum. It took about six hours of cursing, pushing, pulling, crashing, and towing with a wr450 to get it back to the truck. I hate to be a buzz kill but I think you should tear it down.

Paul B
 
For starters, pull the pipe and reed block, that will show you the front and rear of the piston. Better yet, just pull it apart and take some nice photos.
 
plans

In a week or two I plan to send my head off to RB Designs for a squsih-band adjustment, and that will give me the look inside that I need, and I will take compression measurements at that time too.

The bike seems to be running just fine.

I decided to stop worrieng and just go have some fun. that is what these machines are made for.
 
All Good

Its all good.

I think Ron at RBD could definatly do some magic with my 300 head squish-band. However, I think its running just fine.

I took it for a three hour ride at the local hill area and just rode and had fun, and then another ride in the sand dunes. After all of this riding I did another compression test. This time I got 165 lb. on three separate tries, each with 4 0r 5 kicks at wide open therottle (as previously suggested). The results were consistant and well within my expectations. Heck, its even a slight improvement over the previous result of 160 lb..

I did a leak-down test too and she held 165 for 10 min with no signs of leakage. After 10 min. I was satasfied that it was just fine.:D
 
I think the compression test is a good maint tool to check engine condition. If you would let us know what you read when you get the head back, that would be appreciated. I will do the same.

Not sure how gentle of a break in you did, or what prep you did to the cylinder while it was apart, but my guess is the ring had not completely broke in. the comp may improve even more? It seems with the plated cylinders & harder rings it takes more to break them in. Or in another words a proper but not too gentle of breakin procedure. I remember reading some street bike long term reviews & they actually made more power after 20,000 miles etc..

thanks
 
Always remember that a compression test will vary from different altitudes,same bike. We live in MT and start out at 3700 ASL and go up. The 300 KTMs can be down in the 150lbs stock. Most of the time just playing with the base gaskets swap outs and getting that piston a little closer to the top will give another 15 lbs. Lowers port timing a little for some more low end. JMHO
 
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