Holy mother of god
Rebuild failure
- Thread starter Capz85
- Start date
Holy mother of god
Right I've got this thing back in and running, I did a squish test which was giving me 1.3 MM. Which I was pretty surprised about I thought it would have been larger than that
I also did a compression test, after some advice as I'm not sure what it should be and I am concerned about it being too high
I also did a compression test, after some advice as I'm not sure what it should be and I am concerned about it being too high
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More base-gaskets. 1x0,3mm more.
I have 1.6mm squish with 3x1mm gaskets. Piston BDC bottom exhaustport. FLush
What did the 300 make out on dyno??
1.3mm with what basegaskets? From memory, a 250ccm engine 1.3 is ideal. For 300 its 1.6mm if I remember correct.
45rwhp is Ok I guess
My 250 tests at 200 psi but to get there, the engine has to spin for about 10 seconds using the starter.
How many kicks did it take to get to 200 psi for you? If you got that in one kick, then maybe it's too high. Most people on the forum will get around 180-190 psi. This will vary a bit depending on the quality of your tester.
If it took half a dozen kicks to get there you're probably OK. You may find that a 300 is hard to kick over. The bleed port in the cylinder only does so much to relieve compression.
The bleed port may actually skew the results. Maybe a 300 that tests at 180 psi is already at 200 psi considering some pressure is lost out the bleed port.
It took quite a few kicks until t would go any higher
Although I've just had a bit of a heart stopping moment as I looked up the exhaust port and thought I saw marks on my newly re plated cylinder, it's not scored but I can see something
So the std insert in now in showing 180psi
It's not scored but it's a bit worrying as its only ran for 10mins
Although I've just had a bit of a heart stopping moment as I looked up the exhaust port and thought I saw marks on my newly re plated cylinder, it's not scored but I can see something
So the std insert in now in showing 180psi
It's not scored but it's a bit worrying as its only ran for 10mins
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I didn't check the gap, the rings looks ok, everything is new, the cylinder was sent with the piston to be plated to that size
The piston does have slight movement at tdc so I do t think it's really tight or anything I'm hoping it was down to the high compression hopefully it's ok now it's been dropped......
The piston does have slight movement at tdc so I do t think it's really tight or anything I'm hoping it was down to the high compression hopefully it's ok now it's been dropped......
Did you have some information regarding the present tolerances? Mechanical parts are hard to refund.
Just a note, guessing you already know this, but there arent alot of guessing when it comes to engine tolerances and dimensions. 0,5mm (edit; 0,5mm was just example) wrong size in a piston.. well, thats "too much", as in the other way around.
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Jakobi
Super Moderator
I took this thing for a quick ride, everything sounds good until you put it under load around half throttle there's a rattle like its detonating..... Could this all be down to running lean although the plug looks good?
When you pulled it down last you should have measured the trapped volume and calculated the compression ratio. At 1.3mm on a stock head it's probably quite high.
You could try running it richer to see if it cleans the sound up..
but are you sure it's not something else? Rads, pipe vibing, chain slap? and you're just picking up all the sounds that always happen because you're actively listening?
Jakobi
Super Moderator
Just read the whole thread again. Did you end up splitting the cases or just fishing what you could out of the crank with a magnet and flushing?
It all comes down to tolerances. Would be best pulling it down completely, and measuring it all as per spec as it goes back together. If you don't have the right tools to do so, get those parts to people who do.
Is the sound related to rpm, actual chassis speed, or purely throttle position? Where is the ignition timing set?
Yes the cases were split and cleaned out
The noise is only when it's underload around half throttle as pv is opening
I've had the bike running with pv cover off and I can watch it fully operate with no weird noises
My main concern is ruining the cylinder again as it seems similar to the last time
I haven't messed with the timing, but I will go to have a look.
What would change to cause all this?
I've been to my local mx shop, they looked at the cylinder and think the piston is too tight, they also mentioned they have had a couple of cylinders done at the same company as me that came back with faults ..... They will re-hone this next week as its started to scuff and set piston gaps
The noise is only when it's underload around half throttle as pv is opening
I've had the bike running with pv cover off and I can watch it fully operate with no weird noises
My main concern is ruining the cylinder again as it seems similar to the last time
I haven't messed with the timing, but I will go to have a look.
What would change to cause all this?
I've been to my local mx shop, they looked at the cylinder and think the piston is too tight, they also mentioned they have had a couple of cylinders done at the same company as me that came back with faults ..... They will re-hone this next week as its started to scuff and set piston gaps
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What fuel are you running? Regarding compression change.
There is a specific ring-gap range you are supposed to be within. Do a google search on the piston you have, and get the gap correct. If you are taking the barrel off, have it measured, along with the piston.
Or you could send a email to the firm who did the replating and ask what the tolerances was.
Edit: didnt you SM convert your EC300? What jetting do you run? AS1 or AS2 carb?
