Top end knock

Joshua · March 13, 2022, 08:04:06 PM

I had a reputable guy build my motor a while ago. Finally got it legal and took it for a longer ride and when I got back home I noticed some top end knocking. I maybe have 3-4 tanks of gas run through it, so not that many miles on the bike yet. I did have the timing slip, so I reset the timing on it. Just looking for feedback on where to start. It's super disappointing as I haven't even got to enjoy the bike and I'm afraid I'm already troubleshooting problems. My builder has not gotten back to me, so I think he may be MIA. Thanks for any feedback you guys could give me.

https://youtube.com/shorts/APU7rufTpWY?feature=share

Arrow · March 13, 2022, 08:13:03 PM

What ratio premix are you using?

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Joshua · March 13, 2022, 08:35:18 PM

16oz to 5 gallons of gas, 40:1.

Arrow · March 13, 2022, 08:44:40 PM

Ok. That should be alright as long as there is very little full throttle use. The pump kicks out about 20:1 after the 3/4 throttle position.

Sounds like a partial seizure to me. Could have been an air leak too...

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rodneya · March 14, 2022, 10:55:10 AM

If you are sure the noise is from the top end, I would do a leakdown test first to check for leaks. Check what the plugs look like and then pull the head and take a look inside.

m in sc · March 14, 2022, 10:58:02 AM

almost sounds like a small end bearing, but could be a partially collapsed skirt.. id pull the cyls & see whats up.

quocle603 · March 14, 2022, 11:07:05 AM

Clean build. I would inspect everything. When he built your engine, was it both the top and bottom end? What did he replace?

Joshua · March 14, 2022, 05:18:45 PM

Thanks guys. You all know my builder, just don't want to throw him under the bus for something that happens on a crappy day. He built it from the ground up so every piece was touched, replaced, ported, upgraded, new. I know he has been MIA, but he typically would get back to me if I called or texted him, hoping he is alright.

soonerbillz · March 14, 2022, 07:07:23 PM

Make sure you check squish clearance. Could be as simple as a wrong thickness head gasket.

Washerman · March 14, 2022, 07:59:56 PM

Piston slap maybe pull the pipes and take a quick look inside there.

1976RD400C · March 15, 2022, 07:14:39 AM

Agree with the others and lift the cylinders off, then post some pictures if you need help figuring out what's up.

Striker1423 · March 15, 2022, 08:25:28 AM

Sounds like what mine did when it ran on little oil. Pull heads and look.

Joshua · March 15, 2022, 12:03:56 PM

Thanks all. I'll pull them in the next few weeks and update. Appreciate this community, wouldn't have gotten the bike done without everyone here.

pidjones · March 15, 2022, 01:15:00 PM

Wow. Riding season starting up in Florida. Just use a large portion of patience and get it right before setting yourself back for the summer.

rodneya · March 15, 2022, 02:20:51 PM

Quote from: Joshua on March 15, 2022, 12:03:56 PM
Thanks all. I'll pull them in the next few weeks and update. Appreciate this community, wouldn't have gotten the bike done without everyone here.

Wow, you have a lot of patience. I would have had my motor apart within minutes of getting it home. I would just have to know what went wrong or it would bug the s**t outa me.

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Top end knock