Oil leak query

[taz001]

I didn't get a response in this thread: http://www.scootdawg.net/showthread.php?t=52841 , so I'll post again here. I assembled this scooter and after the first two oil leaks rode it 250 miles on the china meter. Now the gasket where the two halfs of the crankcase come together is leaking. Looks as if the gasket is being squeazed out like playdoh:



On the backside of the motor, right in front of the rear wheel. I'm wondering what caused this? Too much crankcase pressure? Or the sealer I used during assembly to seal the gasket:



What does everbody use to seal their gaskets during assembly? Or do you just put them in dry? Any response would be helpful, thanks guys.

[dwint51]

put them in dry

[taz001]

Finally got a response in the other thread. Poster said use a torque wrench for the crankcase bolts. If the seal looking like playdoh being squished out is any indication, I'm inclined to agree. Anybody have the torque specifications for the bolts holding the crankcase together on the 150cc GY6 engine? The specifications can't be the same as the 50cc, right? I mean, more displacement means more crankcase pressure needing more clamping force I would think. I finally purchased a 1/4" drive torque wrench. It goes down to inch pounds, I want to assemble the motor for the black BMS. I've dowloaded several manuals, but they all just give general torque specifications for a range of sizes of bolts, not specific bolts.

[bull]

every nut, bolt, washer, screw and rivet in any application has a torque specification based upon the diameter of the fastener. it is not a function of engine size.

the 6mm nuts used by the Chinese will strip out @ 12 ft lbs of torque. so limit them to 10 ft lbs or under.

8mm will safely take 15 ft lbs and not strip

remember when applying the torque, do it in a cross pattern and in steps - also use a good quality torque wrench with known good accuracy

here is an example of how to torque a 50cc gy6 engine up.
1.. torque all fasteners to 5 ft lbs
2.. wait a couple minutes, recheck the torque
3.. torque to 10 ft lbs, wait again, then recheck
4.. torque the nuts ONLY to 15 ft lbs, wait, recheck

as to gasket dressing; that is a function of the gasket type and whether it was reused or new
Copper Coat spray is best used on base and head gaskets, but it must be allowed to "cure in" and be almost dry

if the paper gasket between the engine halves has a silicone strip, install dry. if it does not have the silicone strip use gasket shellac, but allow it to dry. if you try to install a gasket while it is wet it will get pushed out like your photo shows.

when installing engine half gaskets, remember to check the surfaces for porosity as the aluminum cases sometimes do have porous areas in them which does not seal and causes a loss of clamping force. if you have those they can be fixed with a little two part epoxy like jb weld-- just allow it to cure and shave it flat with a razor before assembly

also sparingly apply a little grey bolt prep on the bolt threads-- near but not at the bottom of the thread-- this seals against weepage through the threads - you can also use (low acetic acid content) rtv silicone if in a jam

[taz001]

Well putting this back together. Going to torque the starter clutch nut. All the manuals I have say 65 ft/lb, but I started to torque it and that felt too tight. Afraid I'm gonna strip the damn thing. Anybody torque their starter clutch nut? To what torque? Thanks guys.

[Miker85085]

I just changed out the cylinder head on a 150cc 157qmj engine due to the previous owner cross threading the spark plug. I replaced the head gasket and put it in dry, then torqued the head bolts after checking the valve clearance to 15 ft lb inches. Drove 20 miles and found an oil leak at the head gasket, so re torqued the head bolts to 20 ft lb checked the valves again and no more leak. Be careful not to tighten them more than 20 ft lbs, use a good torque wrench and use a cross tightening patten. Hope this helps.

[taz001]

Here's a pic to illustrate:



the castellated nut circled in the pic. What does anybody torque it to? I have references that say 65, 40 & 23-25 ft/lbs. What is your reference? Can you sendit to me? If in a manual, what page and approximate page location?

[cheapeto]

http://www.tomantool.com/wrenches.html

I think this what you need. I'd try to google the torque specs to the thread count, the spanner nut is holding. I think that will get you close.

[taz001]

already have the castellated socket to fit it, just need to know the torque setting on the torque wrench. I've about decided on 40 ft/lb.