Dreaded Air Leak.

MercMenace

MercMenace

Mountain Man
Apr 27, 2014
971
164
95
49
Cheyenne, Wy
Just got my jug back from my machinist. Highly recommended. If anyone is in the cheyenne area. GPO is the name of the shop. Local Yamaha dealer here uses him exclusively. Charges 65 bucks. PO bored twice. Had to go .030 over.

Jug installed, cold new compression test just under 120psi. Bike started 2nd kick. Warmed up, idled great. Took it around the block. Easy going. Got home idle raced to full throttle. Shut her down immediately. Let her cool. Went to grab my leak down tester. Ran the damn thing over in my excitement to pull her out of the garage. Smashed to hell and bent up. Scrapping the whole thing making a new one. Although I am suspecting a crank case seal as my fresh oil is gone from the sight glass.

I really like pics and guides so my threads tend to be more like how to books. Sharing knowledge isbthe root to combating ignorance. Bear with me.

Got another project going on today So I won't make the tester til tonight.
 
Was it putting out stinky smoke? That's the sign of a clutch side crank seal.

Some good places to check for the air leak, reed cage gaskets, carb boot, exhaust flange, base gasket(green paper no good), crank seals, the case, oil injection nipple on carb, head gasket.

Once you build your new tester, I'm sure you'll find it.
 
No stinky smoke. I drained all the gear oil. Its a 25 year old machine so knowing the PO had lots of other mistakes, I figured I'd drain the metallic oil out and put in fresh. Rather than waste the money on yamalube now. I did a 25w30 with intention of changing after 1 hour of riding. Then fill with yamalube.

I will find the leak.....leaks. one by one ill pressure test 100 times before I start it again if I have to.
 
Id much rather take the time and do right, now, miss abit at the beginning of the season. Cause later my buddies will surely be counting all the times I pull out my wallet, and laughing cause I'm an idiot.
 
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Did my leak test today. Couldn't even get it to 5 psi. Practically soaked the motor in soap looking for the major leak. After about a half hour realized I forgot the rubber on the exhaust port. Felt like an idiot. After feeling like Sherlock's inept third molar I got it to nine lbs for about 3 seconds. Had a buddy keep pumping while I sprayed looked and listened..nothing, not a single bubble. Coupled with the fact that my gear oil is missing I ordered a crankcase seal.. in the back of my mind I'm contemplating a full lower rebuild.
 
Did you Check the crank seal behind the stator as well?
If that gear oil is missing, that would be a culprit also.
Maybe try putting the gearbox breather tubing in some water, if it is pressurizing, it will bubble and you know its leaking in there.

For what its worth, These bottom end's are fairly easy to do, Hell even I did one. It might be better for you to go in there, fix all the surprises, and know what you have when its done.
 
Yeah that's the one I ordered. I'm being hesitant to rebuild it unless I really need to. If jon decides he hates it then it becomes mine and then it gets garaged and built for me. Trying to keep it close to stock for him. If he decides he likes it then I will do it to keep him rolling. If I do it for me its going to get a +3 stroker and all the goodies.
 
I think the worst part of this process is, that once everything is sorted out I still have to break it in. I've only ridden it twice. Both times it didn't rip like it should. so im looking at mid season before can actually open this baby up.
 
After the rebuild you should have done three heat cycles followed by retourqing the bolts on the jug and head. Taking it for a ride down the street hardly qualifies. The time to leak test was before you ever fired it up.
 
MercMenace said:
Oh I know! Excitement is a powerful influence on doing things wrong. :)
Click to expand...

Been there, effed that :oops:

Other than testing and spark plug I think all possible sites have been covered. No major oil leaks from sprocket, kicker, or clutch shaft? When doing rt seal, seal collar and key to shaft with 3bond (etc), they sometimes leak there.
 
Decided to pull the trigger and do a complete rebuild. I have a couple questions though? I am getting in contact with Ken to see if he has a rebuilt crank for sale, but i am curious about +4mm hotrods kit? I can get one off ebay with bearings and gaskets for 239 shipped. What else is involved with the strokers? do i need a new piston? are the gaskets and bearings any good?

Any and all info would be appreciated.
 
MercMenace said:
Decided to pull the trigger and do a complete rebuild. I have a couple questions though? I am getting in contact with Ken to see if he has a rebuilt crank for sale, but i am curious about +4mm hotrods kit? I can get one off ebay with bearings and gaskets for 239 shipped. What else is involved with the strokers? do i need a new piston? are the gaskets and bearings any good?

Any and all info would be appreciated.
Click to expand...

Cases need to be trenched, spacer or cut head for certain. Might be few other details.
Vito's has SS cranks for $112. 3mil is $179.
 
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