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Anyone know about checking spigot to head clearances?

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jeffyjeff
World Chat Champion



Joined: 02 May 2020
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PostPosted: 05:03 - 11 May 2025    Post subject: Reply with quote
How does the cylinder look? scored? crosshatch intact? Are you going to hone it before assembly? What is the end gap spec for the rings? That fragmented compression ring might expedite oil migration past the spigot, but you said the second ring was holding good compression. interesting.
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History shows again and again how nature points out the folly of men - BOC
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Robby
Dirty Old Man



Joined: 16 May 2002
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PostPosted: 06:01 - 11 May 2025    Post subject: Reply with quote
Whenever I think about doing my own highly unique project, I just read one of the threads about the Bullet 612 to set me straight.

I like spannering and I like a tricky problem to solve, but some of the problems you've found would drive me up the wall. At least it's a good example of what can happen when you push an engine way past it's design.
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stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
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PostPosted: 07:43 - 11 May 2025    Post subject: Reply with quote
jeffyjeff wrote:
How does the cylinder look? scored? crosshatch intact? Are you going to hone it before assembly? What is the end gap spec for the rings? That fragmented compression ring might expedite oil migration past the spigot, but you said the second ring was holding good compression. interesting.


Cross hatching gone so it'll need a hone (actually done ready for reassembly). There's a visible smear on the bore from a previous incident where a piston broke through the gudgeon pin hole and was hitting the skirt off the bore but nothing you can catch with a fingernail and it'll have done 5 or 6000 miles since then. I'll check end gap when I get the new rings (the second one broke on removal) but there are very wide tolerances on these motors and again, no step on the bore you can feel.

Yeah, I was surprised how well it's been sealing, there was a fair bit of carbon and staining above the middle ring but everything shiny and clean below it. The intact portion of the top ring will have been opposite the gap in the middle one. Also no real sign of excessive amounts of oily carbon on top of the piston or in the head. I've seen more blowpast on a bullet with fully intact rings
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
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stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
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PostPosted: 07:52 - 11 May 2025    Post subject: Reply with quote
Robby wrote:
Whenever I think about doing my own highly unique project, I just read one of the threads about the Bullet 612 to set me straight.

I like spannering and I like a tricky problem to solve, but some of the problems you've found would drive me up the wall. At least it's a good example of what can happen when you push an engine way past it's design.


Yeah, I didn't go into it blind. However, I do actually get to ride it and do quite a lot of miles on it. I've done a couple of tours in Northern Spain on it and I get it up into the Highlands 3 or 4 times a year. It's massively fun to ride.

The engineering aspect is a good mental break for me and it's all pretty simple stuff comparatively. My job is effectively problem solving based on signs and symptoms, making lists of what could cause them and eliminating possabilities so I'm fairly good at getting my head round things. It's sat with the whole top end off just now. I reckon on it being 2-3 hours before it's back in a position to start and ride it once the new rings arrive.

I can do a full top end rebuild on it in less time than it takes to change the radiator hoses on the wifes CBR600.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
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