Lets see how smart u guys are.......

[LIVE2RIDE Powersports]

I'm having having a prob with my compression.

I had a wetjet 61x 701 with stock 165psi. Since the motor sat for awhile i redid the topend with WSM plat 1 over topend. 710cc, Had the cylinders bored and dropped the cylinders in, had great clearance on a feeler gauge, put a westcoast head with 29cc domes on it and it was 145psi in both, so i put some 26cc domes, Which was told i get over 200psi. I got 165psi. Same as stock.

The ski ripped all summer, no complaints. I ordered a OP head that the guy had at 215psi, put it on and got 150. I know the engine was built right cuz my friend builds race engines for a living. He ported it and said it was from a templete called (stairstepper). He told me he didnt touch the exhaust port, so that shouldnt be the problem. I can't imagine having a leak with steady comp and a great running motor. I am running a stock head and base gasket. 55 thou on head, not sure base.


What am i missing?

OP head that make 215 at sea level should make around 180 in the midwest right. It doesn't drop that much.


Would i need a bigger head since i went to 710cc?

Any thoughts?

 

[Matt_E]

Have you measured and confirmed that the piston clearances are within specs?

I had a very similar issue with a big bore topend that was sold to me as 84mm, with 84mm pistons.
Turns out it was too big for even 84.5 pistons, so it needed a slight bore to get to 85.

 

[LIVE2RIDE Powersports]

Have you measured and confirmed that the piston clearances are within specs?

I had a very similar issue with a big bore topend that was sold to me as 84mm, with 84mm pistons.
Turns out it was too big for even 84.5 pistons, so it needed a slight bore to get to 85.

We havn't since it was installed. He said it was good clearance. We even did the squish and was good, we tried using a copper 16 thou head gasket he made, but we couldnt get a good seal..

What should specs be?

 

[blaster800]

with this table you can correct your compression for different altitudes : Compression Test Altitude Compensation Factors
Altitude Factor
500 0.987
1500 0.960
2500 0.933
3500 0.907
4500 0.880
5500 0.853
6500 0.826
7500 0.800

8500


0.773

A standard compression reading of about 150 psi at sea level in Los Angeles would measure significantly less in the surrounding mountains. For example, at an elevation of 6000 feet, the expected reading would be 150 psi X .8359 = 125 psi. The cylinders would be reading low if compared to sea level measurements, yet perfectly fine at this altitude.

 

[Matt_E]

We havn't since it was installed. He said it was good clearance. We even did the squish and was good, we tried using a copper 16 thou head gasket he made, but we couldnt get a good seal..

What should specs be?

Squish has nothing to do with piston clearance.

Double-check those clearances. They shouldn't be any bigger than 4 thousandths of an inch with cast pistons, if that much.
Piston clearance = bore - piston diameter.

 

[LIVE2RIDE Powersports]

Squish has nothing to do with piston clearance.

Double-check those clearances. They shouldn't be any bigger than 4 thousandths of an inch with cast pistons, if that much.
Piston clearance = bore - piston diameter.

I will check again. When we put it together it was 3k

 

[MADMAT]

Compression gauge:veryhappy:

 

[LIVE2RIDE Powersports]

Compression gauge:veryhappy:

Same from my crappy napa gauge, a snapon gauge, and his which is like a 300 dollar setup he bought when he taught a engineering class and worked at the airlines.

I wanted to think it was my 9 dollar gauge, but after trying them all, its pretty close.

 

[MADMAT]

lol...I just figured I would throw it out there....

 

[Motorheads5]

What is the ring gap ?

 

[akula]

The pro-tek catalog lists the compression for a 29 cc chamber @ 245psi 61x piston and 29cc chamber 230psi 62t piston do you have 61x type pistons

 

[LIVE2RIDE Powersports]

What is the ring gap ?

I will check that and the clearance soon.

 

[LIVE2RIDE Powersports]

The pro-tek catalog lists the compression for a 29 cc chamber @ 245psi 61x piston and 29cc chamber 230psi 62t piston do you have 61x type pistons

61x.. 29cc's were like 140-145, and 26cc's were 165. Wasn't expecting that.

The motor still ripped my arms off this summer, but i want more.

 

[orangefinger]

Westcoast head requires OEM head gasket which = 7cc, if you use 26cc domes you add 7cc = 33cc which resolves in your compression...

I think the smallest westcoast domes still out there are 25cc...

this is obviously for sea level

 

[Motorheads5]

What he is saying is the same dome read's 15 psi different between a 61x piston v.s. a 62t piston are you sure you have 61x piston's ?

 

[LIVE2RIDE Powersports]

What he is saying is the same dome read's 15 psi different between a 61x piston v.s. a 62t piston are you sure you have 61x piston's ?

I just looked at the box they came in. They say 61x, unless its stamped wrong.

 

[SurferSmurf]

Compression gauge

that was my first thought. i did a compresion test one day just for chits and grins and my motor read 130 each cylinder. i about flipped out cuz the week before it was 165. bought a new guage and it was right back at 165.

 

[MADMAT]

Yea I had some really weird readings once too....and bought a new harbor freight one and bam back at 190..

 

[Motorheads5]

I am gonna buy a programmable one that will give me what I want Dammnit

 

[LIVE2RIDE Powersports]

that was my first thought. i did a compresion test one day just for chits and grins and my motor read 130 each cylinder. i about flipped out cuz the week before it was 165. bought a new guage and it was right back at 165.

Yea I had some really weird readings once too....and bought a new harbor freight one and bam back at 190..

Wish mine was that easy and cheap to fix. It's ok, im building a big bore now and putn this in my wifes ski. Still want the comp to be right. It worries me that maybe now there is a ring gap or something.