Compression problems, pleasee help!!!

[EaCastillo00]

Hello guys how are you? well thing is i recently did my top end, bought brand new cilinders, rings, pistons, gaskets, did this like 4 months ago and i have used it for about 2 hours, mostly beach riding, havent gone trailing yet, ive used 32:1 oil ratio, pump gas, recently i started having problems turning it on, went to my mechanic and did a compression test, it says 60psi! we get the cool head out and check the cilinders and pistons for wear, they are like new! no scratches, no tears, no dents, everything looks as if it was built yesterday, only thing we notice is pistons have a little play, could it be a ring failure? another thing, once i get it to turn on it works perfectly, it runs good, pipes are not dripping oil, the are dry, it doesnt consume oil from the tranny, doesnt overheat, and turns on everytime once i get it to turn on the first time. help dont know what to do, should i try and throw some new rings in it?

[bigweav81]

What brand of cylinders? What did the rings look like? If you bought the cheap niche / eBay cylinder kit your mechanic probably should've chamfered the edges of port Windows. They are sharp af.

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[EaCastillo00]

No, they were not niche,  lets say the port windows edges were sharp, what kind of damage could they make? would they damage the rings? because the cilinder walls are neat, no scratches no dents, only the small play i mentioned before

[trickedcarbine]

Verify it all looks good. Make another attempt at assembly. Do a compression rest again with a known to be good tester. If ot still shows something weird, do a leak down.

[booxzzy]

Compression tester might be broken, does it show same compression on both cylinders? 

 

[booxzzy]

Did you try new fuel, did you check the spark plugs, vacuum leaks? 

There is quite few things you should check before you get the new pair of rings. 

[EaCastillo00]

2 hours ago, booxzzy said:

Did you try new fuel, did you check the spark plugs, vacuum leaks? 

There is quite few things you should check before you get the new pair of rings. 

Ok, will try, but would that explain the low compression?

[booxzzy]

Nope but is the compression same on both sides? 

[blowit]

Guess I feel compelled to offer my input.  

The first thing I might question is the mechanic.  We may not have the full story but it sounds like the bike has a starting problem but otherwise runs good.  A comp value of 60psi, unless you are on Mt Everest, would be pretty much not running at all.  I would first question that value.  Seen this tooooo many times where guys end up doing a total rebuild over a poor compression test.  The adapter that screws into the head is just as important as the gauge.  

Personally, I would pull the pipes and/or the reed blocks to get a good look at the rings.  At 60psi and those hours, either your rings are welded into the pistons, or you have no problem at all.  If the ports were so sharp that they destroyed the rings in a couple hours, that usually leaves some evidence in the bore, or a quick feel will tell you.  

 

 

Yes, it is normal for the pistons to look a little "loose" from the top.  The top timing edge of the piston is designed smaller due to how it expands when hot.  A sharp mechanic can simply move the piston around at TDC and determine if the rings are welded or not.  

 

To me this sounds like a choke problem. Not pulling it all the way out to the second click, cross tube is missing, etc, etc.  Something simple

 

Brandon

Mull Engineering

 

[EaCastillo00]

On 6/6/2017 at 4:13 PM, blowit said:

Guess I feel compelled to offer my input.  

The first thing I might question is the mechanic.  We may not have the full story but it sounds like the bike has a starting problem but otherwise runs good.  A comp value of 60psi, unless you are on Mt Everest, would be pretty much not running at all.  I would first question that value.  Seen this tooooo many times where guys end up doing a total rebuild over a poor compression test.  The adapter that screws into the head is just as important as the gauge.  

Personally, I would pull the pipes and/or the reed blocks to get a good look at the rings.  At 60psi and those hours, either your rings are welded into the pistons, or you have no problem at all.  If the ports were so sharp that they destroyed the rings in a couple hours, that usually leaves some evidence in the bore, or a quick feel will tell you.  

 

 

Yes, it is normal for the pistons to look a little "loose" from the top.  The top timing edge of the piston is designed smaller due to how it expands when hot.  A sharp mechanic can simply move the piston around at TDC and determine if the rings are welded or not.  

 

To me this sounds like a choke problem. Not pulling it all the way out to the second click, cross tube is missing, etc, etc.  Something simple

 

Brandon

Mull Engineering

 

Yes, as i said, thing looks neat, as if i had just rebuilt it, and once i get to turn it on, it runs good, it idles perfectly, pipes dry, im gonna do what you told me with another mechanic, check the rings, and see what they say, and try a compresion test with another tester, the place i live in is 300 mts over sea level, so i guess that if the engine had 60 psi it wouldnt turn on, would it?

Edited June 8, 2017 by EaCastillo00