Post by wideload on Jan 16, 2011 0:24:50 GMT -5
Lapping the valves has turned out to be more challenging than I imagined.
After lapping the valves to a nice mate finish, I tested the seal by pouring liquid into the upturned combustion chamber. One of the exhaust valves leaked. After disassembling the valve assembly and relapping 3 times, I got a liquid proof seal. That is when I was told a simple liquid test is not good enough. You need to run compressed air past the underside of the valve and watch for bubbles in the liquid in the combustion chamber. Now, that test indicated three leaking valves. I tried several more passes with grinding compound and even switched from a lapping stick to using fuel line to turn the valve stem. Still no air-tight seal.
It was about this time, after loosing track of the number of repeated disassembly/reassembly trials, I read about using coarse followed by fine lapping compound. OK. I tried that. I started with the Permatex (grit size not identified) sold by MikesXS, then followed with the coarse and fine shown in the picture below. I purchased the Coarse/Fine kit at Checker and it is really some bad stuff. Instead of a smooth finish, it produced a bunch of concentric ridges on the valve face and seat. Of corse they now leak worse than ever.
I am absolutely stumped. Could someone recommend a coarse/fine compound kit I could get at an auto supply store (so I don't have to wait for mail delivery). Better yet, is there a different way to check the seal? I am beginning to think the compressed air inspection will never indicate a perfect seal.
MikesXS sells the Permatex it seems to be the most coarse compound in the batch. The Checker course/fine kit does not seem suitable for lapping.
After lapping the valves to a nice mate finish, I tested the seal by pouring liquid into the upturned combustion chamber. One of the exhaust valves leaked. After disassembling the valve assembly and relapping 3 times, I got a liquid proof seal. That is when I was told a simple liquid test is not good enough. You need to run compressed air past the underside of the valve and watch for bubbles in the liquid in the combustion chamber. Now, that test indicated three leaking valves. I tried several more passes with grinding compound and even switched from a lapping stick to using fuel line to turn the valve stem. Still no air-tight seal.
It was about this time, after loosing track of the number of repeated disassembly/reassembly trials, I read about using coarse followed by fine lapping compound. OK. I tried that. I started with the Permatex (grit size not identified) sold by MikesXS, then followed with the coarse and fine shown in the picture below. I purchased the Coarse/Fine kit at Checker and it is really some bad stuff. Instead of a smooth finish, it produced a bunch of concentric ridges on the valve face and seat. Of corse they now leak worse than ever.
I am absolutely stumped. Could someone recommend a coarse/fine compound kit I could get at an auto supply store (so I don't have to wait for mail delivery). Better yet, is there a different way to check the seal? I am beginning to think the compressed air inspection will never indicate a perfect seal.
MikesXS sells the Permatex it seems to be the most coarse compound in the batch. The Checker course/fine kit does not seem suitable for lapping.