engine noise when hot

[MrJslade]

Hello fellow blaster owners. I just had a polaris trailblazer 250 bored out got it all together and its sound great when you first crank it up but when it gets warm its starts to make a metal on metal tapping noise. The lower rod bearing seemed good as i could not detect any play. The rist pin had some where that I could feel and when placed in the rod with the needle bearing it could be wiggled instead of beaing tight. It was not bad though and with the new ristpin and needle bearing it only had a very small amount of play. I whould not expect that the bearing whould make the noise becouse it did not feel that bad. And also would an upper rod bearing not make noise when cold and then make noise when hot. It seems like as the rod expands as it gets hot the rist pin whould also. So does anyone have any ideas.

Thanks
jslade

oh yea polaris sucks yamaha rules

 

[motoman9911]

What type of oil are you using? In the crank

 

[MrJslade]

$15 a quart castor oil i think its called

 

[MrJslade]

By the way there is no trany or clutch in this engine. The centrifical clutch hooks externally directly to the crank.

 

[brandoz28]

you are using 4 stroke oil, not 2 stroke oil right?

 

[MrJslade]

nope its a 250 2 stroke so i am using castor 2 stroke oil mixed 32:1

 

[brandoz28]

ahhh ok...for some reason i was thinking that was a 4 stroke bike lol.

 

[motoman9911]

I meant to say the tranny. What oil is in your tranny?

 

[MrJslade]

The gear box is seperate. There is no tranny or clutch in the engine. The centrifical clutch hooks externally directly to the crank. Theses trailblazers are wierd machines i personally hate it. The blaster is so much easier to work on and the parts are much cheaper.

 

[motoman9911]

Oh yeah, that's right. I don't know what I was thinking. My dad has a Scrambler. Have you ever checked the compression when the engine gets hot?

 

[MrJslade]

I did a compression check when i insalled the new piston in fresh bore. I got 65 PSI. I am in the process of breaking it in. Its been raining a lot so i havent had a chance to ride much and probably only has 25 minutes on it so no i have not done that but its freshly bored and suposedly has .0027 inches piston to cylinder clerance.

 

[motoman9911]

Only 65psi? That's really low.

 

[brandoz28]

i agree, thats really low even if they haven't seated yet

 

[MrJslade]

Low for a blaster but i think that is ok for one of these machines. I have read that over 100psi is good. The compression ratio is 6.1:1 i think. I will check copression again hot and cold.

 

[MrJslade]

Yep the compression ratio is 6.11. Does anyone know how to convert to psi? I think you just mutiply by atmospheric pressure (14.7) that would only be 89 psi that doesnt seem right.

 

[Kgibson]

Sounds like the piston is tapping the head. I would check the squish.

 

[MrJslade]

Yep sorry yall were right. I checked my compression gauge and it was wack. I figure there more like 95 psi. And I think the compression on a broke in machine is like 130 psi.