i just want to get it running - compression issue.

[bign1514]

I can not figure out my low compression issue. I have a ported cycl. and running a ADA head with 33cc domes. My front cycl. is getting 190 psi and my rear 140 psi. The cycl. sleeves are in good shape. nothing there that would concern me.

I switch my domes around thinking it was a bad o-ring. Problem still there.

Whats the next thing? Replace my rings?

Is there a way to test the piston rings?

thanks for any help - i just wanna ride!

 

[chrisdoc0608]

pull the cylinder and check rings and pistons

 

[bign1514]

everything looked good. I did poor some oil in the cycl and compression shot up! I am guessing this mean new rings?

Would you replace both piston rings or just the cycl. lacking compression?

 

[Mike W]

everything looked good. I did poor some oil in the cycl and compression shot up! I am guessing this mean new rings?

Would you replace both piston rings or just the cycl. lacking compression?

Replace rings in both cylinders along with honing the cylinders.

 

[chrisdoc0608]

Replace rings in both cylinders along with honing the cylinders.

X2

 

[bign1514]

even if the cycl. still have the cross pattern inside.... still get the cycl honed?


thanks for the information!

 

[bign1514]

i also have a nice pair of 82mm wiseco pistons with rings... with about an hour of ride time on them. The wiseco pistons require a bigger clearance.

Would it be better to replace the cast OEM 82mm pistons with the wiseco 82mm or just buy new rings for the OEM with a hone?

Or better to take the 82mm wiseco pistons and get them bored correctly. Since the rings have about an hour on them, would it be safe without replacing the rings?

 

[chrisdoc0608]

its your call, but when you replace rings its a good idea to hone as well

 

[bign1514]

here is a picture of the wiseco pistons.... would any scratches (nothing deep, took my finger nail across and couldn't feel anything) cause any problems if I went with the siseco pistons?

thanks!

i would buy rings for either OEM or wiseco pistons with a hone. Trying to figure out which piston i should go with.

 

[bign1514]

pics...

 

[uncleuno]

This happened to me when I ported my cylinder. I had 185 psi compression then I ported my cylinder it went to 135 psi so I bought smaller domes now its good . I knew the compression would drop but not 50 psi maybe that could be it .

 

[WFO Speedracer]

This happened to me when I ported my cylinder. I had 185 psi compression then I ported my cylinder it went to 135 psi so I bought smaller domes now its good . I knew the compression would drop but not 50 psi maybe that could be it .

THOSE PISTONS ARE CASHED,I WOULDN'T RUN THEM!oke:

 

[orangefinger]

I think the pistons dont look so good, but to tell the truth ( and i know this is really pushing it ) I had the same pistons like that and I got new rings and actualy dremel smoothend that piston and it has been running over 2 years now with no problems.....looool..

 

[bign1514]

what would cause them to be cashed? they barely have a total of an hour of use?

can you maybe sanded them down a little bit?

 

[Matt_E]

This happened to me when I ported my cylinder. I had 185 psi compression then I ported my cylinder it went to 135 psi so I bought smaller domes now its good . I knew the compression would drop but not 50 psi maybe that could be it .

The OP is seeing a dramatically lower compression in only one side.
So, unless one side is ported and the other is not, this explanation makes no sense.


Judging from the pictures, I have to ask....what's you piston-to-wall clearance?

Also, take a good look at the rods. It's possible that the low side is bent, resulting in lower stroke than the good side. (Due to water ingestion/hydrolock)

 

[bign1514]

This happened to me when I ported my cylinder. I had 185 psi compression then I ported my cylinder it went to 135 psi so I bought smaller domes now its good . I knew the compression would drop but not 50 psi maybe that could be it .

please note this quote does not contain to my issue. This is another members comment on there pasted problem.

I have a new crank, with ported cycl. from a rep. shop.

Can the pistons in the pictures above be saved in any way?

 

[WFO Speedracer]

what would cause them to be cashed? they barely have a total of an hour of use?

can you maybe sanded them down a little bit?

It dosen't matter if they have two minutes or two hundred operating hours on them,those pistons are cashed,I have seen pistons destroyed in less than five minutes due to improper jetting,air leaks or improper clearance.These pistons fell victim to one of those errors.:buttkick:

 

[chrisdoc0608]

you need to re hone/ bore the cylinder to match a good set of pistons along with new rings. I also agree with matt, you need to check your wall clearance. IMO those pistons look like they suffered a seizure at some point

 

[Matt_E]

Before going to buy any parts, check some measurements and check the crank.
Don't just throw parts at it.

 

[bign1514]

well... this has been a great learning project (way too expensive BTW).... but this was the first modified engine i rebuilt. I could of caused the piston to seize during tuning the carbs.
As i hate to spend more money, i just want to ride and ride with a motor that is right. I will send the cycl. off and get the work done right and enjoy the rest of the riding season - instead of wrenching and playing the guessing game.

Thanks for all the information and advice. this site kicks azz by the way!