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Hey guys, i tore the base gasket on my 47cc dirt bike engine and was wondering if I can use rtv silicone for instead of a gasket. If so do I put some on the crankcase, let it dry, then assemble cylinder. Or just assemble while still sticky. I know that's not the best way to use rtv but it's better than getting it all over the transfer ports and in the crankcase.
 

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MidnightMidbikeSyndicate
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Hey guys, i tore the base gasket on my 47cc dirt bike engine and was wondering if I can use rtv silicone for instead of a gasket. If so do I put some on the crankcase, let it dry, then assemble cylinder. Or just assemble while still sticky. I know that's not the best way to use rtv but it's better than getting it all over the transfer ports and in the crankcase.
Don't use that crap it wont hold up! Use a thin layer of JB weld. It tightens up the squish too so you end up with more compression too :D Thin layer is all you need, to remove the head for future work, simply give it a tap with a rubber mallet on the exhaust port and she will pop right off. Lots of us do that here. Cheers.
 

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I used Yamabond myself, RTV is not good around oil and gas, it's more for water pumps and valve cover gaskets. I used the Ultra high temp RTV 750* F. on my C1 intake, it did seal the intake but the parts separated right off when I took them off and were oily. JB Weld you have to heat the parts or soak then in Acetone. Yamabond ( Yamaha ) will peel right off after disassembly. What ever you use it has to be really thin, to gain compression. PB Parts in Florida, all there copper base gaskets are .010" not .020" like stock or even the old .025" paper base gaskets. That's what gasket my A2 Cag B/B kit came with, losing .020" was like night and day for compression.
 

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Remember, the base gasket is not the head gasket, there is only lower case pressure there, 15-20lbs.?? The compression is in between the rings, piston top and cap. Both surface need to be clean, I have the piston in the cylinder attached to the rod at TDC w/ piston inside. I spread the Yamabond thin on the cases and drop the cyld down add the 4 bolts just lightly touching the cyld base, for at least one half hour, just a hair more on the bolts. Let it sit all night and then torque. JB Weld dries a lot faster, so you would tighten them different.
 

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Track Racer|Bike Builder
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@EPR - i will be attempting my first complete rebuild of a cag enginge what do you consider "Thin" for Yamabond instead of the paper base gasket the kit came with? thanks for any advice.
 

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I apply it as thin an as little as possible, .005" when compressed. Yamabond or Hondabond just works good, they use it on intake manifolds and gaskets and rubber tubes to seal. Its sticky and dries fast, that's why I have the cyld w/ piston & rings inside and ready to drop. put a small bead around the case seal area, smooth it out, and wipe extra goo off the engine case sides. If it is on too think it will bead up on the inside seam, an might break off and get inside the engine.
Ok, other options, a paper base gasket is upto.025" thick, and stock copper is .020", and at pocketbikeparts online store under MT-A1 or A2 hp parts, they have .010" copper gaskets. On the copper gaskets I use Permatex high temp copper head gasket spray, great stuff.
The main reason for using Yamabond is to lower the cyld on the cases and raise the compression.
 

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you can use RTV but 2 stroke mix brakes it down really fast that's why we prefer to use the yamabond or hondabond ( or a motorcycle equivalent for 2 strokes ) like EPR is saying apply thin if you see it squeeze out on the outside then it's almost guaranteed that it squeezed out on the inside as well...
 

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Track Racer|Bike Builder
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Thanks EPR I couldn't get Yamabond at my Yamaha dealer here in Stockton - they were closed for the holidays?? Any way I went to Jorgys Suzuki and they recommended a $28 tube of ThreeBond hahaha but also had ThreeBond 1184 Grey for $14. I used it to seal the case and as a base gasket. Stuff works great, I have a lifetime supply now. Build turned out strong just waiting on a pumper carb via FedEx. Thanks again for all the info in this forum that guided me through my first complete rebuild. The donor bike is the one with the sticker on the tank.
 

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just a quick tip you should check your crank end play if you did not use a case gasket sometimes it works out but most of the time without a case gasket the end play can be to tight or worse none at all and it will kill the crank bearings
 

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Nice work, like the blue and yellow bike. Engine looks great, you used paper case gasket right and sealed the cylinder with your sealer right?? You need a 3rd bearing clutch housing there about $15 to your door if you know where to look. Here is a balanced clutch photo. So, you waiting for a pumper carb, what did you get???

Stockton, they have a track at the Fairgrounds where they race Go Karts and pocket bikes, its a great track and was one of the track on the Mini Moto Racing Teams.
 

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Track Racer|Bike Builder
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yes paper on the case Thanks for the clutch balance tip I'll give it a try. I ordered the carb and manifold from pocketbikeparts.com (pics below)hope it fits and works better than the Dell O clone I have they are absolute junk it's jb welded to the manifold and I rigged 4 springs to help hold it in place I also had to order a easy recoil flywheel and starter the (the kind that grabs more in the middle) higher compression has mangled 3 pull starters plastic and aluminum cogs both and is killing my hand. I know about the track out here and have been planning stop by to see if there are any opportunities to ride out there, their website is jacked right now thanks again to all for the help.
 

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I live 35 west of Santa Rosa CA. off HWY116 and The Russian River. Well, sounds like you have enough compression, lol. Yeah the stock stuff don't work on a hopped up engine. Does your flywheel have the spring loaded arms. I have a few of those 15.88m China clone Walbro WT-603 carbs, they work pretty good and easy to adj. 2 spring loaded screws, low and high jets. Its has a gas return line you will have to deal with. Now you need a 16mm alum V-stack and 44mm ID air filter. Yes you have the right intake manifold. Online on the .com davesmotors in Utah has all kinds of carbs and stacks & hp air filters, look under scooters. I would not lighten the new flywheel, that's for stock engines, you need the weight and the engine will start easier. Get your self a thick leather welding glove.
 

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