79' Yamaha yz400 swapped blaster help!!

B0NE22c · 2022-09-15T22:23:03-0400

I have a 95' blaster with a 79' yz400 swapped into it and I'm currently in the process of getting it running but I've hit a roadblock of compression. The engine feels like it has really high compression when I kick it over but when I put the compression tester on it gets a hair over 30psi of compression. I've had the sparkplug out and there's no resistance. I'm ordering new rings but after that I'm lost any ideas?

pygmy warrior · 2022-09-16T07:42:09-0400

You should get 30 psi with no rings! Remove the head and have a look. Hopefully you don't a hole in the piston.

B0NE22c · 2022-09-16T12:47:56-0400

pygmy warrior said:
You should get 30 psi with no rings! Remove the head and have a look. Hopefully you don't a hole in the piston.

I took off the head there isn't a hole in the piston and the cylinder walls look fine there is sme scratches but my finger nail doesn't get caught on them. I'm guessing the next step is removing the jug and checking the rings.

pygmy warrior · 2022-09-19T08:35:06-0400

How did the head gasket look? It could be a blown head gasket and/or warped head. Lap the head with sandpaper on a flat surface like glass or granite countertop.

B0NE22c · 2022-09-20T22:38:55-0400

pygmy warrior said:
How did the head gasket look? It could be a blown head gasket and/or warped head. Lap the head with sandpaper on a flat surface like glass or granite countertop.

It looks fine I did see some black on the mating surface of the head and what looked like exhaust residue on the cooling fins I'll aso add I haven't gotten it to start its only belched fire out the exhaust port

pygmy warrior · 2022-09-21T08:32:28-0400

When you reassemble the head gasket use this on both sides.

https://www.autozone.com/sealants-glues-adhesives-and-tape/sealant/p/permatex-copper-high-temperature-spray-a-gasket-sealant-9-oz/520940_0_0?cmpid=PLA:US:EN:AD:NL:1000000:GEN:10758688450&gclid=Cj0KCQjw7KqZBhCBARIsAI-fTKLQubIJmd1Bpv45CK0qfNUPsKOhMtU5w2QIc2lRPVaY2VP0_fLa6M8aAnSwEALw_wcB&gclsrc=aw.ds

B0NE22c · 2022-10-25T20:23:03-0400

pygmy warrior said:
When you reassemble the head gasket use this on both sides.
https://www.autozone.com/sealants-glues-adhesives-and-tape/sealant/p/permatex-copper-high-temperature-spray-a-gasket-sealant-9-oz/520940_0_0?cmpid=PLA:US:EN:AD:NL:1000000:GEN:10758688450&gclid=Cj0KCQjw7KqZBhCBARIsAI-fTKLQubIJmd1Bpv45CK0qfNUPsKOhMtU5w2QIc2lRPVaY2VP0_fLa6M8aAnSwEALw_wcB&gclsrc=aw.ds

I apologize for it being so long since I last responded. I lapped the head and cleaned both the jug mating surface and reassembled it. I did a compression test again this time it gets a tick over 60psi but it's enough compression to get it to fire on starter fluid.

BigBoy_Bikers · 2022-12-25T05:06:58-0500

The engine feels find it irresistible has in reality high compression when i kick it over but after i placed the compression tester on it gets a hair over 30psi of compression. I have had the sparkplug out and there may be no resistance. I'm ordering new rings however after that i'm misplaced any thoughts?

jaguar · 2022-12-29T19:21:53-0500

A lot of compression testers are just not very good. Go up one level of expense for the purchase of another one. If you buy from Amazon then read the comments about it to make sure others like it.

79' Yamaha yz400 swapped blaster help!!

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