302 compression ?? External fuel tank??

[blueskyracer]

Just did a compression test on my 302 engine and the top cylinder is reading 108 and the bottom cylinder is reading 120. To me the 108 is not good.

My other question is are 102 rings the same as 302 rings? I know the pistons are different but thought maybe the rings are the same.

Are the rings and cylinder walls the only thing that could cause low compression? With a 4 stroke it could also be valves but 2 strokes to me are greek! They either run ar they don't. Building boats is much easier Another project to add to the list!

Thanks

[Tim Weber]

Same rings, yes 108 is not so good.

The top cylinder may have got too hot and caused the rings to lose tension, maybe the head had a slight leak.

If you change the rings and head gasket, it should be good to go.

Tim

[blueskyracer]

Same rings, yes 108 is not so good.

The top cylinder may have got too hot and caused the rings to lose tension, maybe the head had a slight leak.

If you change the rings and head gasket, it should be good to go.

Tim

Thanks Tim, I have a new gasket and 102 rings in stock.

[Islandmon]

Mike just wondering if you roped the top cyl until the gauge would not move any further. Sometimes guys will pull once or twice and think that's enough, you need to give it at least four good pulls. Not saying your one of them, just checking though because I've made that mistake.

If I'm not mistaken the compression range should be between 120 and 135 with no more than 5 lbs difference between each cyl. I'm sure there are some guys out there more qualified than I am, let's hope they chime in here.

Sam,

[blueskyracer]

Mike just wondering if you roped the top cyl until the gauge would not move any further. Sometimes guys will pull once or twice and think that's enough, you need to give it at least four good pulls. Not saying your one of them, just checking though because I've made that mistake.

If I'm not mistaken the compression range should be between 120 and 135 with no more than 5 lbs difference between each cyl. I'm sure there are some guys out there more qualified than I am, let's hope they chime in here.

Sam,

Sam, I roped each cylinder 7 times using a snap-on compression testor

[raceright]

Just did a compression test on my 302 engine and the top cylinder is reading 108 and the bottom cylinder is reading 120. To me the 108 is not good.

My other question is are 102 rings the same as 302 rings? I know the pistons are different but thought maybe the rings are the same.

Are the rings and cylinder walls the only thing that could cause low compression? With a 4 stroke it could also be valves but 2 strokes to me are greek! They either run ar they don't. Building boats is much easier Another project to add to the list!

Thanks

Funny thing compression---if engine's been sitting around for a while top cylinder could be dry. Hence oil drain to bottom and now compression raised.
Best to check compression right after running. But reringing over winter is best idea anyway.

Pat

[Islandmon]

Sam, I roped each cylinder 7 times using a snap-on compression testor

That's a nice tester, I need to invest in more of a brand name gauge.

[guedo499]

Just did a compression test on my 302 engine and the top cylinder is reading 108 and the bottom cylinder is reading 120. To me the 108 is not good.

The only thing I would worry about is that the two cylinders are not reading similar compression. The OSY motor that I run has much less than 100 lbs in each cylinder....

[blueskyracer]

The only thing I would worry about is that the two cylinders are not reading similar compression. The OSY motor that I run has much less than 100 lbs in each cylinder....

True John, I am not worried about the 108 but the difference in the two. I am just going to tear it down, hone and replace the rings

[Tomtall]

Overheat

If you can do this with your old rings,they got toooooo HOT!

[me-otch]

Geeze! Thats not a healthy looking ring!

Not to jack this thread but when you cc your 302 whats the minimum legal cc's you can have?

I just got a used BONE stock Yamato 302 this past season from Ron Hill and raced it the way it came. I havent don anything to it yet...not even the prop shaft change.

[fcliff]

Min CC

via the inspection manual; 26.0cc for heads with 18 mm plugs and 25.5cc for heads with 14mm plugs.

[Islandmon]

via the inspection manual; 26.0cc for heads with 18 mm plugs and 25.5cc for heads with 14mm plugs.

Can anyone tell me why the 00.5 difference between the 18mm and 14mm plugs......Hmmm ?

Thx,

Sam

[fcliff]

cc's are measured at the top of the plug hole. The 18mm plug hole uses an additional .5 cc over the 14mm plug. The combustion chamber is the same for both heads.

[seanp3]

The only thing I would worry about is that the two cylinders are not reading similar compression. The OSY motor that I run has much less than 100 lbs in each cylinder....

Do you think we still have enough metal in those sleeves to give it a light hone and new rings over the winter? We might want to think about that