just rebuilt top end and now not much compression:y is this?

[zxcvbnm]

hi i just rebuilt me top end on my (2000 honda xr100 single cilender dirt bike). by rebuildig my top end i meen boring it over size and putting new rings in, oh and i also had to put in a new head. yea so anyways i put it all together and tryed to start my bike it did not start and it felt like it had pretty low compresion, so im woundering if there is any thing i could have done wroung to make this like this. this is my first engine rebuld so i might have did something wroung. today though right before it got dark i noteced that there was no spark so im gona check that out tomorrow its probly just a wire unplugged or something, so that is one reason y it wasent starting, but still it felt like low compresion. any ideas y it would have low compression. thanks

[Ichy]

How did you bore it oversize? You have used over sized rings as well? Did you check the piston was ok for the new bore?

The only way to really check the compression is with a gauge. I was surprised how weak the compression felt on a small bore bike I was recently working on although a compression check gave 118psi. Sort out the spark first.
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[Blue_SV650S]

Its fairly easy to get the cam/cam chain one tooth out. You might think you have it in line, you then release the cam chain tensioner and its actually a tooth out.

How did you compress the rings when you put it back together?

The new head ... was it from a 'trusted' source? (valves might be bent or burnt).

Finally how did you set the valve clearances?
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[Ariel Badger]

You bored it oversize and fitted oversize rings....... Did you fit an oversize piston as well?
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[zxcvbnm]

how would being a tooth out make it have low compression? oh and yea the rings and piston are both.25 oversize, and the piston does fit good it the bore i guess. i compressed the rings with me hands. i got the head from a mechanic i took it too, it was a used head that he found lying around his shop, i bought it off him for 100 bucks so it better be good! i set the valve clearances by inserting a .002 flat feeler gauge under it. i have a service manual for the bike so i used that alot. to bore it oversize i took it to my mechanic and he sent it some where else to get bored. i hope my mechanic dident give me something wrong because he was a real cheap guy and all he cared about is money. he even gave me a piston from a 2001 xr100, the rings in that are totally different then the 2000xr100. but he gave me 2001 pistion too so i think it should be ok. oh and one more thing i had to take the head on and off a couple of times, do u think i runed the head gasket and now its not sealing well. because the first time i put it on it had oil all over it, but thats because i dident tighten the bolts that hold the head/cylender on tight enough. maybe your right and i just think is low but its aculy not i donno, anyways : thanks

[Blue_SV650S]