freshly rebuilt engine is hotter on one side (pics)

[sfab]

heres the deal, ive built a 61x bigbore on 61x case, bored it to 85mm. ive put everything back together and start it up to chk if everything is working as planned. chk with the caompression gauge and got 165-160lbs. went on the lake to do the break-in. after idling the motor for 5 min, ive uped the rpm a bit, just to make the ski move a bit faster. after 10 min of circling around ive started to punch the gas without going any further than 1/3 throttle. impressive power at midrange altho it will need a bit of tuning. was doing this for about 10min and then the engine started to loose power just like it was running on one cylinder. went to the dock, chked a couple of things, compression, sparkplug, everythings seems to be good. went for another ride and it was still running weird. i decided to check my cylinder for anything suspect. this is what i found:

excessive oil retention on one side (very hot side water jacket):

i really dont know what happen, it was running nicely for about 10 min... the cylinder with the dark piston was really hot. Ignition? i havent check the reed to see if theres a leak on one side. does it looks like it was running reallly lean on one side? piston clearance is 0.0045" for those Pro-X. it was honed by a a pro so im pretty sure its not a faulty cylinder. any idea? thank you

 

[superjetkev]

the one cyl doesnt even look like it was firing. twin carb or single? thats all i cAN come up with

 

[sfab]

the one cyl doesnt even look like it was firing. twin carb or single? thats all i cAN come up with

single 48mm lamey mega flow
i swear it was running good for 10min. when i opened up the engine i was surprise how clean the other one was. plugs were firing at both cylinder, ive cheked that too.

 

[Matt_E]

I think an oring might be leaking water into the clean cylinder.

 

[sfab]

I think an oring might be leaking water into the clean cylinder.

but both of the domes oring were new and intact when i remove the head. and why the other cylinder was freakin hot? the dark piston looks like it was toasted... maaan i hope its something like an air leak or mixture related cause im starting to freak out a bit... :frown:
btw thanks for your inputs!!!

 

[aqua]

i would think the compression check would show if an oring was bad. if your orings were intact and fine i would start wondering about your carbueration...black piston would be lean and the other might be really really rich.

things i would check.

pressure test case for leak.
compression
spark in both cyl
carburation

 

[douglee25]

That black piston looks suspect now. I'm not sure if it's the picture or not, but the crown looks damaged now, no? I'm trying to think how the hell you could have a brand new motor with a black piston like that in 20 minutes or less? Did you install the head correctly with the water outlets on the carb side? What kind of coil are you running? I would cut back both plug wires and be sure they aren't broken. Recheck your jetting. Was it the same jetting that you previously ran the ski on (last year or whenever)? Did you change anything else?

Doug

 

[junkman]

air leak, reeds?

 

[Jr.]

The "Black" side is the side that is running. The clean side is being washed out by water ( or so it looks from the pics) Check o-rings, Ex man gasket, also check to see if the sleeve dropped.

There is also a chance, you are not firing on that cyl? Check your spark.
Fuel will wash you clean also, but there is always some residue the pics are not showing. Can't really tell?

My first guess would be water!

 

[sfab]

air leak, reeds?

i removed the intake manifold last night, they were all in place and it looks they were doing there job. ive changed the intake gasket for a brand new, ive reused the old one since it was in nice shape. anyway ive removed the engine from the hull for further investigations. but im wondering how a air leak can suddenly make an engine run like ********, at low rpm...

 

[SJBrit]

but im wondering how a air leak can suddenly make an engine run like ********, at low rpm...

Because it's a water leak? My money is on a dropped sleeve.

 

[sfab]

The "Black" side is the side that is running. The clean side is being washed out by water ( or so it looks from the pics) Check o-rings, Ex man gasket, also check to see if the sleeve dropped.

There is also a chance, you are not firing on that cyl? Check your spark.
Fuel will wash you clean also, but there is always some residue the pics are not showing. Can't really tell?

My first guess would be water!

yep ive noticed my sleeve have dropped a bit. i didnt press them in place when ive heated up the cylinder, ive simply droped them in. the hot side was the one that drop the most, about 0.006" and the clean side 0.002"-0.003. ive already deck the cylinder flush again at my shop. im still wondering how it can make the cylinder overheating...

 

[sfab]

Because it's a water leak? My money is on a dropped sleeve.

i guess youre right, i will reassembled the engine this afternoon and see if it runs nicely again.
thank you very much guys for the help!! very appreciated

 

[SJBrit]

The cylinder with all the residue looks like it's running way lean, which would make it run hot. I think that cylinder is fine if you get the jets right. The clean/cold cylinder is the one with the problem....

 

[Jr.]

If you just decked the cyl, You DID NOT cure the problem!!
It will more than likely happen again!!!!

You need to re-heat the cyl & hold the sleeves down in a press until it cools & then deck. The sleeves will push up during cooling, that is what happened in the first place!!!

 

[sfab]

If you just decked the cyl, You DID NOT cure the problem!!
It will more than likely happen again!!!!

You need to re-heat the cyl & hold the sleeves down in a press until it cools & then deck. The sleeves will push up during cooling, that is what happened in the first place!!!

i will try that. i should have put the oem head on the cylinder to prevent this. thanks all!

 

[sfab]

aaaaahh its working and you wont believe what was the trouble...

a spark plug!!!

at least ive corrected the droping sleeve problem...

 

[SJBrit]

Doh!! Always start with the simple stuff :biggthumpup: It's so tempting to attribute cause to whatever you were last tinkering with though: a couple of weekends ago I spent a while rejetting my low end - I'd been running rich. At one point it seemed like I'd got way too lean, so I started going back up in jets. Took a while to figure out the jets were fine: I was running out of gas!! at:

 

[Octane]

I had the exsact problem today with my 61x while running it in. I think i`ve tracked it down to the ht caps.

The coil metered ok at the lead but the black plastic connector between lead and plug was open circut at the rear and the front one was high. My rear pot was washed clean and the front was firing, when doing a visual on the plugs both where firing.

It`s a new motor but i`m using the old coil/leads & plugs caps.

The photo`s are an absolute double of mine.