Tearing out my engine, need experienced eye on things..

[nickt916]

Im taking some parts out and selling them in the for sale section, and since i have some room to work with i decided to check out since the guy i bought it from said "it was" rebuilt last august some "20 hours" ago. I checked compression and it came to 135psi on both sides.

Also my exhaust was leaking smoking like crazy inside the hood, come to find out it was a ripped coupler, and some oil over time leaked through the coupler hole and inside the hull, making it a bit slippery and slimy, so thus giving me another reason to pull everything out.

i pulled the head and im not really sure how to tell if it needs a rebuild or not, with 135psi id assume its getting to the point. Also it says 50 on the pistons, does that mean it was bored .50 over? i tried to take the best pictures i could to share what i have to see if anyone can point something out and give me some pointers. Id like to rebuild the top end anyways since i already got it torn, but not sure if i need a .50 over kit or does 50 mean something totaly different.

thanks!

PS. cylinders look like they are scratched up but thats reflection from the rough cylinders tops.

 

[mosquini]

are you going to be rebuilding that motor your self? if so I would look at the ports ans see it the guy before you tryed to do his own port job, if so I would send it out to a proffesional too look at it. Where are you located? Do you have acces to some inside calipers(mic)?

 

[nickt916]

are you going to be rebuilding that motor your self? if so I would look at the ports ans see it the guy before you tryed to do his own port job, if so I would send it out to a proffesional too look at it. Where are you located? Do you have acces to some inside calipers(mic)?

well im not even sure that i need a rebuilt, or just get a gasket kit instead. I would rebuild just the top end since its been rebuilt .5 over and carbon build up is not that bad so that tells me that it hasnt been done long ago. But i still dont like the 135psi, someone told me maybe head gasket was leaking not torque right? i dont know what inside calipers are

 

[douglee25]

Put each piston down into the bore and check for scoring, etc. That could be a sign that it needs to be rebuilt. It doesn't appear that the head gasket was leaking because I see good piston wash and the gasket doesn't appear to be breached. Did you check with a 2nd gauge to verify if those readings were correct?

Doug

 

[keefer]

I would not think that 135 on a stock engine would be cause for alarm. They were designed to run on 87 octane so the compression was low on purpose. I agree that the gauge used might be reading low. Not for sure but I thought that they were supposed to be at about 155 on an accurate gauge. If the readings were the same in both cyls then that engine is probably ok if it was rebuilt properly 20 hours ago. Check the cyl walls for any heavy scoring, if they look good put a new Yamaha stock head gasket on that thing and run it unless you want to step it up and get a nice aftermarket o-ring head and bump the comp up to 180 or so. You will need 93 octane but it will run a whole lot stronger.. Good Luck:biggthumpup:

 

[beachedflunkey]

The last three motors I've seen with that low of compression either had stuck or improperly gapped piston rings. They should be gapped at .012. I think +/- .004 is okay but don't quote me on that.

 

[WaveDemon]

I would not think that 135 on a stock engine would be cause for alarm.

since they are even it might be the gauge.

 

[oxnard111]

since they are even it might be the gauge.

I did a comparison of a harbor frieght gauge to my buddy's Snap-On. His always reads about 25-28 lbs more than my cheap gauge. I still use mine to check if compression is even between the two cylinders.

 

[keefer]

I did a comparison of a harbor frieght gauge to my buddy's Snap-On. His always reads about 25-28 lbs more than my cheap gauge. I still use mine to check if compression is even between the two cylinders.

Yep, my Craftsman gauge reads 15-20 lower than the Snap On that I have now.

 

[#ZERO]

Take a picture of the exhaust port and transfer ports while each piston is at bottom dead center. Post some more pictures so we can see the cylinder bore and ports.

If you have to bore the cylinder make it 1mm over because the piston in there is .5mm oversize.

PM sent.

 

[nickt916]

Take a picture of the exhaust port and transfer ports while each piston is at bottom dead center. Post some more pictures so we can see the cylinder bore and ports.

If you have to bore the cylinder make it 1mm over because the piston in there is .5mm oversize.

PM sent.

yea ill do that in a few minutes, i hope its just a gasket itself and not torqued right, bolts seemed a bit looser than i expected when i was taking them off.

Put each piston down into the bore and check for scoring, etc. That could be a sign that it needs to be rebuilt. It doesn't appear that the head gasket was leaking because I see good piston wash and the gasket doesn't appear to be breached. Did you check with a 2nd gauge to verify if those readings were correct?

Doug

i dont know what "scoring" is. You are right about the gasket. I did not check with a 2nd gauge to verify the readings, this is why i did the reading on my stock 99 superjet to make sure the gauge was working correctly, and i got 150psi on both cylinders, but that jet is in excellent condition and has low hours on a never touched engine. So i knew it was correct. But like you said about the gasket, it might be that i only need a new head gasket and torqued correctly

 

[nickt916]

looks in great shape as far as that goes, it does looks ported, the one thing im wondering is about the ring gaps in the reply bellow, seems like the ring gaps are a little bit to much?

 

[nickt916]

I pushed the cylinder over to the side as much as i could to see the rings even a bit to be able to take a picture... Im not sure what my options are at the moment. I can just get a new head gasket and torque it correctly, or if i should go as far as getting new rings, then get cylinder and head gaskets and put on ADA head and leave it at.

 

[beachedflunkey]

If you need to get a new head gasket anyway, get a base gasket while you are at it after you check out the rings with a proper feeler gauge and inspect the grooves.

Pages 5-11 thru 5-13 of the service manual discuss inspecting the pistons and all. Somebody just recently posted a link to where you could download it from.

 

[headshock]

I have a manual inline if you want I can e-mail it to you (pm me your e-mail address). Might as well order a whole gasket kit and an extra head gasket while your ordering things, this way you will have a spare if you ever need it.

 

[wydopen]

i remember reading in the original ad for that ski that it was ported

 

[Matt_E]

It is ported.

The transfers have been cleaned up, and the exhaust widened quite a bit.

 

[#ZERO]

Here is the online manual. http://www.drmikesandy.com/xh2o/Yamaha SuperJet Service Manual.pdf

The cylinder still has the still cross hatch from the last over bore also the porting looks very good. The only thing I would be concerned about is the ring gap, it looks huge and I don't think just installing a set of rings will fix that problem.

Forget the stock head gasket and go with an ADA Girdled Head. Install it with just the stock head bolts and run another compression test.

 

[nickt916]

The piston does seem to move around inside the cylinder a bit, is this normal or 2 strokes? because from my experience from rebuilding car engines the pistons are supposed to barrely fit inside the cylinders even without the rings. Good test on a car is to oil the cylinder, take a piston without rings and put it inside the cylinder... it should slowly lower itself under its own weight and not drop straight through. i dont know much about 2 strokers.

I have a manual inline if you want I can e-mail it to you (pm me your e-mail address). Might as well order a whole gasket kit and an extra head gasket while your ordering things, this way you will have a spare if you ever need it.

yes please email it to me Nickt916@yahoo.com, do you know where i can order individual gaskets and not kits? seems like most places just sell kits.

 

[nickt916]

yanked the motor, not gonna clean up that messy hull and start from scratch :arms: