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Author Topic: 1982 CB750F... The resto-not  (Read 18365 times)

Offline Jimbonaut

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1982 CB750F... The resto-not
« Reply #260 on: Feb 10, 2019, 21:28:27 »
Insulators?  What be they - another name for the cam guides?
« Last Edit: Feb 10, 2019, 23:05:35 by The Jimbonaut »
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Offline irk miller

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Re: 1982 CB750F... The resto-not
« Reply #261 on: Feb 10, 2019, 23:25:50 »
Insulators?  What be they - another name for the cam guides?
What most people call the carb boots are actually called insulators.  They're numbered, so you don't have to worry about mixing them up, and they're a different size for the head side and the carb side.

Offline Jimbonaut

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1982 CB750F... The resto-not
« Reply #262 on: Feb 10, 2019, 23:50:35 »
Ah, those things. I’ve been calling them jug boots. Yeah, I need to get those things off, but it’s so damn cold in my garage they’re rock solid. Need to - ahem - borrow the wife’s hair dryer and soften them up a bit.

Fuck it’s cold here. “How cold is it?”  So cold I saw a cop tazering himself to keep warm.


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« Last Edit: Feb 11, 2019, 00:10:30 by The Jimbonaut »
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Offline doc_rot

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Re: 1982 CB750F... The resto-not
« Reply #263 on: Feb 11, 2019, 00:13:42 »
I would replace the base gasket otherwise you probably will be tearing it down later to replace it anyway. Doesn't matter about the timing marks, you will have to re-time the cams upon assembly. I would also consider measuring the cylinder bores to see if they're out of spec and if that checked out I personally would do a flex hone and maybe new rings. Just takes one cheapy engine rebuild to make you do it twice, but to each their own
« Last Edit: Feb 11, 2019, 00:26:20 by doc_rot »

Offline pidjones

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Re: 1982 CB750F... The resto-not
« Reply #264 on: Feb 11, 2019, 07:21:57 »
If you post about the boots on an F site, you will be corrected. They say it is because their search engine won't find it unless you use insulator. I've used a heat gun to soften the boots both for installation and removal of the carbs. And that is in a heated garage. It helps to keep from cracking the old rubber. I also smear a light bit of silicone vacuum grease on them to install, but that may not be necessary. At least the last time I didn't have to used a ratchet strap to assist installing them. Maybe third time is the charm, 'cause they finally are all four working and not leaking. Hint: hook up throttle cables BEFORE putting the carbs on the insulators. I prop the at ~45 degree angle part-way behind the head to hook them up, the lower them in position and commence heating the insulators.
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Offline advCo

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Re: 1982 CB750F... The resto-not
« Reply #265 on: Feb 11, 2019, 09:14:36 »
There ya go Jim. Looks like you've got a couple burnt up looking exhaust valves so wouldn't hurt to make sure they are all still sealing up (alcohol in the ports test) and you'll definitely want to check your valve clearances and probably loosen those particular exhaust valves up a bit.

Offline Jimbonaut

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Re: 1982 CB750F... The resto-not
« Reply #266 on: Feb 11, 2019, 10:45:42 »
Thanks chaps so that's what a burnt valve looks like.  Knew pulling the head was going to school me.  Pretty sure I did the alcohol test with the KLR but will need a revise on the process - essentially I'm looking to see how tightly the valves seal by pouring alcohol into the ports, correct?  Both intake and exhaust?

Doc, good advice.  I wasn't really planning on doing a complete top-end rebuild, largely because it seems (to amateur me at least) largely unnecessary.  The compression is was excellent (hopefully will be again once I put everything back together again) and so I didn't plan on going any deeper than necessary.  That said, I was looking at the jugs yesterday thinking, well, I've got this far...

Pulled all the side covers, oil pan and whatever else I could off the crankcase - not long before it's ready to paint.  Thanks for the info on the timing - it's starting to make more sense now.  I can't get my head around the importance of the timing mark before pulling the cams, but I totally get the importance of getting that mark in the right place before putting them back.

That happened yesterday, but not before the first decent skate of the year.  When you live in the deep freeze, you take the perks where you can get 'em.



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Offline advCo

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Re: 1982 CB750F... The resto-not
« Reply #267 on: Feb 11, 2019, 11:09:44 »
Man, its been years since I've skated. We used to have a blast playing pond hockey when we were younger.

To check the valves, pour alcohol (not beer  ;D) into the intakes, give it a good 20 minutes or an hour or so and check for any leaks. Take note, empty and dry them out and repeat on the other side.

Offline irk miller

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Re: 1982 CB750F... The resto-not
« Reply #268 on: Feb 11, 2019, 11:10:27 »
Just because they're light, or appear a little lean, doesn't mean the valves are burnt.  A burnt valve will literally have part of it's edge melted away.  As the pressurized and fuel rich, super heated air is looking for oxygen, it takes the path of least resistance.  Once it finds its weak point, it always pushes through that spot, melting it away.  If you had good compression, then it is unlikely that the valves are burnt, as they would hold little or no compression. 

Also, nothing wrong with just going with a hone and putting it back together.  Depends on how deep down this rabbit hole you want to go.

Offline Jimbonaut

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Re: 1982 CB750F... The resto-not
« Reply #269 on: Feb 11, 2019, 12:56:37 »
Excellent Nick, I'll do that.  Any excuse to pick up some alcohol.

Just because they're light, or appear a little lean, doesn't mean the valves are burnt.  A burnt valve will literally have part of it's edge melted away.  As the pressurized and fuel rich, super heated air is looking for oxygen, it takes the path of least resistance.  Once it finds its weak point, it always pushes through that spot, melting it away.  If you had good compression, then it is unlikely that the valves are burnt, as they would hold little or no compression. 

Also, nothing wrong with just going with a hone and putting it back together.  Depends on how deep down this rabbit hole you want to go.

How deep indeed.  Call it good and leave the jugs as they are or go full-on Heart Of Darkness on the thing.  Either way, I think you've helped me name the bike - Colonel Kurtz, take a bow.
"I'm telling you Donnie, nuthin' but nuthin' but right"