Other Help me understand my damage.

[OCD Solutions]

I need to understand how this happens so it doesn't happen again. It is a seadoo 951 Ported and bored out 4th over. This engine has less than 4 hours on a fresh rebuild, had 165psi compression to start and the plugs were always a nice color. I always ran Amsoil Dominator oil mixed at 40:1 with Premium fuel. I have some ideas but I want to see what some of you engine builders spot and figure out.

The port job was done by a Skidoo guy that may have assumed that certain concepts cross over that maybe do not? 1mm wider and 1 mm higher on the exhaust port was all the specs I got. Ring end gap was .016" and piston clearance was 0.006" (measured roughly with a feeler gauge and divided by 2, not the best way but all I have.)

Not sure if its needed but I was running a Rossier head with 49cc domes, Novi/Dean intake with dual Novi 48's and a Coffman pipe. Advent ignition with Coffman pipe timing curve.

Anyway, let the CSI'ing begin.

 

[waterfreak]

maybe your engine was running a little hot! Those marks on the pistons seem to indicate lack of lubrication that may of been a result of overheating.

Disclaimer: that's just a guess based on the pics and is only my opinion.

 

[OCD Solutions]

I am open to all opinions, If I am doing something wrong I need to know what it is.

At first I was thinking i wasn't allowing enough warmup time for the wiseco's but all my other engines are fine. The other thing is my practice of starting the ski on the trailer, am I running it too long without cooling water? Firing it up without lubrication after it's sat for too long?

 

[Matt_E]

Seizure after not letting it warm up will be a "four-corner" seizure, and yours doesn't look like that.

 

[OCD Solutions]

Does it look lean? I ran a Hottach with dual probes and my temps were always under 1200F. I tuned for 1150 max at WOT.

 

[OCD Solutions]

What about poorly matched components? Porting/Pipe combination?

 

[MES4888]

It is a heat issue, having the corners scored like that is a tell tale sign. If it were an oil/lube issue you would have scoring around the entire cylinder/piston. I would call and get the exact specs for piston to wall and ring end. I know from working on sea doos at the dealership here that they tend to be pretty well cooled stock, so you may want to look into this. Is this in your SJ or in a couch? Either way lets see your plugs and check your cooling system. Fresh or salt water too?

 

[OCD Solutions]

It's in my couch but all that doesn't matter much, I have torn the ski down and am parting it out anyway, I just want to know so I don't make any mistakes on future engines or pass on bad components to someone else.

 

[ATS_Scott]

What was your cylinder/ piston wall clearance? Maybe it just wasn't enough.

 

[OCD Solutions]

what was your cylinder/ piston wall clearance? Maybe it just wasn't enough.

0.0055"

 

[WFO Speedracer]

0.055"

On what kind of pistons?

 

[OCD Solutions]

Wiseco's

 

[WFO Speedracer]

Wiseco's

There is no way you can run Wiseco pistons in that big of a bore with that kind of clearance,the growth of the forged pistons will not allow it,I usually set the WSM's up a .0055-.0060 piston to wall on a 951 and they are cast,Wisecos would have to have somewhere in the neighborhood of .0070-.0080 to work properly in that application.

 

[OCD Solutions]

There's your answer then, Thanks everyone.

 

[fast superjet chase]

i run .003 in my big bore with wisecos and havent had a problem

 

[Matt_E]

In what engine?

 

[Idok]

I need to understand how this happens so it doesn't happen again. It is a seadoo 951 Ported and bored out 4th over. This engine has less than 4 hours on a fresh rebuild, had 165psi compression to start and the plugs were always a nice color. I always ran Amsoil Dominator oil mixed at 40:1 with Premium fuel. I have some ideas but I want to see what some of you engine builders spot and figure out.

The port job was done by a Skidoo guy that may have assumed that certain concepts cross over that maybe do not? 1mm wider and 1 mm higher on the exhaust port was all the specs I got. Ring end gap was .016" and piston clearance was 0.006" (measured roughly with a feeler gauge and divided by 2, not the best way but all I have.)

Not sure if its needed but I was running a Rossier head with 49cc domes, Novi/Dean intake with dual Novi 48's and a Coffman pipe. Advent ignition with Coffman pipe timing curve.

Anyway, let the CSI'ing begin.

:ugh2:

 

[OL JS Rider]

looks like a deffinate over heat prob to me. I would never want more than .005 cl to piston clearnace on a fresh engine. last set of weiscos i used spec at .004 altho this was not a jet ski. I would look for a cooling system blockage or restriction.

 

[WFO Speedracer]

i run .003 in my big bore with wisecos and havent had a problem

I don't know of an engine bigger than 50cc's that you can run wisecos in with .003 piston to wall clearance

looks like a deffinate over heat prob to me. I would never want more than .005 cl to piston clearnace on a fresh engine. last set of weiscos i used spec at .004 altho this was not a jet ski. I would look for a cooling system blockage or restriction.

That would work fine with something with a very small bore and long stroke,the 951 has just the opposite it runs an 88mm bore,with his it was at 89mm,the bigger pistons expand more which requires more clearance,Seadoo also run a decent amout of compression around 150 psi.Typically Wisecos run .001-.002 more piston to wall than cast pistons.

When I first started working at the Seadoo stealership Rotax was running the 580's with .0025mm piston to wall clearance,it required a lengthy break in time and left no room for error.The best thing I ever did was up the clearance to .004mm like every other engine was running at the time.

You have two choices when it comes to piston to wall clearance,you can put in the correct clearance to start with or you can let the engine find the proper clearance,I prefer the former approach to the latter.

 

[SUPERTUNE]

There is no way you can run Wiseco pistons in that big of a bore with that kind of clearance,the growth of the forged pistons will not allow it,I usually set the WSM's up a .0055-.0060 piston to wall on a 951 and they are cast,Wisecos would have to have somewhere in the neighborhood of .0070-.0080 to work properly in that application.

I don't know of an engine bigger than 50cc's that you can run wisecos in with .003 piston to wall clearance



psi.Typically Wisecos run .001-.002 more piston to wall than cast pistons.


You have two choices when it comes to piston to wall clearance,you can put in the correct clearance to start with or you can let the engine find the proper clearance,I prefer the former approach to the latter.

I'll agree! Way to tight on the piston clearance and the ring gaps are too tight as well!
Not a jetting issue for what I can see from these limited pics, need to see the inside of the piston crowns too...
1150 should be about right depending where the probes are mounted from the skirt face. The closer you move the EGT prob to the piston, the lower degrees you need.