Author Topic: Cobra motor disassembly and rebuild  (Read 106059 times)

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Offline edwardmorris

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Re: Cobra motor disassembly and rebuild
« Reply #50 on: December 17, 2015, 10:59:12 AM »
Close. It's a piece of foreign material. We use them all the time......Let's see engine out,been in engine room for a couple months , plugs out....hmmmmm checked with boroscope and blew air in plug hole... should have opened a valve and blew through there. The air moved it that you could see. So what is it? Pic later, Bill
I'll take an unlikely guess: Temp oil leak stop putty or antisieze?

Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Cobra motor disassembly and rebuild
« Reply #51 on: December 17, 2015, 11:15:21 AM »
Is it the spark plug cap?
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline 754

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Re: Cobra motor disassembly and rebuild
« Reply #52 on: December 17, 2015, 11:20:56 AM »
Is it an electric cooled pony harness jack ?
...code words for cut off end of tie wrap...ftp://
« Last Edit: December 17, 2015, 02:27:05 PM by 754 »
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Offline madmtnmotors

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Re: Cobra motor disassembly and rebuild
« Reply #53 on: December 17, 2015, 11:28:12 AM »
Muffler bearing?
TAMTF...


Wilbur



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Offline Bill/BentON Racing

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Re: Cobra motor disassembly and rebuild
« Reply #54 on: December 17, 2015, 01:37:46 PM »
Drum roll, don't ask me how.  F me silly. It was the cut off head of a tie wrap...smh!  >:( ::) ;D, Bill
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Offline gschuld

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Re: Cobra motor disassembly and rebuild
« Reply #55 on: December 17, 2015, 02:19:41 PM »
That was my very next guess ::)    :)

George

Offline Restoration Fan

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Re: Cobra motor disassembly and rebuild
« Reply #56 on: December 17, 2015, 03:15:28 PM »
Drum roll, don't ask me how.  F me silly. It was the cut off head of a tie wrap...smh!  >:( ::) ;D, Bill
So you're saying that "Baby Face's chew toy" might have been correct then?  ;D
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Offline Bill/BentON Racing

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Re: Cobra motor disassembly and rebuild
« Reply #57 on: December 17, 2015, 04:47:02 PM »
Well it was plastic! Looks like old number 2 gave up the ghost
somewhere along the line. 3's on 3, 1s on 4, 4's on 2, and 4's on 1. 1,3 and 4 were probably original to crank. Lost number 2, either moved others for clearance or ignorance!  ;D Can't figure it out yet. Cases ground on 1&2. Bolts on rods which were ground on are 3&4. Well, I'll probably use the other 4 RC
steel H/D marked properly and installed correctly.Plastigage time. We will see, lots of options. Bill.
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Offline Bill/BentON Racing

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Re: Cobra motor disassembly and rebuild
« Reply #58 on: December 17, 2015, 04:51:33 PM »
The tapered pins are exactly like my old NOS set leftover from a Drag Specialties closeout sale. 39 grams.
BentON Racing Website
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______________________________________
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Offline Bill/BentON Racing

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Re: Cobra motor disassembly and rebuild
« Reply #59 on: December 17, 2015, 05:10:18 PM »
Maybe use these rods.
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______________________________________
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Offline MRieck

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Re: Cobra motor disassembly and rebuild
« Reply #60 on: December 17, 2015, 05:19:40 PM »
Well it was plastic! Looks like old number 2 gave up the ghost
somewhere along the line. 3's on 3, 1s on 4, 4's on 2, and 4's on 1. 1,3 and 4 were probably original to crank. Lost number 2, either moved others for clearance or ignorance!  ;D Can't figure it out yet. Cases ground on 1&2. Bolts on rods which were ground on are 3&4. Well, I'll probably use the other 4 RC
steel H/D marked properly and installed correctly.Plastigage time. We will see, lots of options. Bill.
Looks to me like rod bolts are ground on 2 & 3 Bill.  Looks like a lot of shenanigans with that crank set up Bill. ::)
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Offline Bill/BentON Racing

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Re: Cobra motor disassembly and rebuild
« Reply #61 on: December 17, 2015, 05:28:29 PM »
They are ground on 2&3. But the rods now on 2&3 were on 4&3. 3 still has the rod that came on it. The rod on 2 was number 4 early on! Yes, lots of decisions. ...we can always throw this in the mix!! Bill
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______________________________________
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Offline cbr954

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Re: Cobra motor disassembly and rebuild
« Reply #62 on: December 17, 2015, 05:44:07 PM »
Are those shorter rods or do you have stroker pistons?
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Offline gschuld

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Re: Cobra motor disassembly and rebuild
« Reply #63 on: December 17, 2015, 06:16:22 PM »
Don't bring out the welded up stroker crank and shorty golden rods Billy, you know it will only agrivate Mike's health condition.  ;D


Offline Bill/BentON Racing

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Re: Cobra motor disassembly and rebuild
« Reply #64 on: December 17, 2015, 06:24:37 PM »
 ;D, stock length Mike luvs old #$%*.....on the shelf!! Lol. ;D
BentON Racing Website
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Over 35 years of experience working on vintage motorcycles, with a speciality in Honda SOHC/4 with a focus on the CB750 and other models as well from 1966 - 1985.
______________________________________
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Offline gschuld

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Re: Cobra motor disassembly and rebuild
« Reply #65 on: December 17, 2015, 06:53:02 PM »
Yea, save that stroker setup for the "go for broke" motor that you won't cry if it let's go on you.

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Offline dragracer

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Re: Cobra motor disassembly and rebuild
« Reply #66 on: December 17, 2015, 08:12:27 PM »
In the real world, it doesn't matter what rod is where as long as they're all  the same weight. Unless the builder was using old bearings to  clarify. With the appropriate new bearings, clearance would be fine for any rod placed in any position.  Explain to me in simple terms how those numbers stamped on the rods affect function in that scenario. . I'm not an SOHC guru like you fellas but I have built a lot of engines. Now if we're talking pistons, I'd be concerned that they were mixed from one hole to the next due to wear characteristics. From my point of view, I have to acknowledge that this is a dragbike engine, its seen a lot of hard passes over its life, there will be failures from time to time so if we're looking for perfection, don't buy used motors.

Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Cobra motor disassembly and rebuild
« Reply #67 on: December 17, 2015, 09:44:31 PM »
Bolt heads appear different. maybe not ground. Mix and match  ;)
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline calj737

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Re: Cobra motor disassembly and rebuild
« Reply #68 on: December 17, 2015, 09:55:27 PM »
LMAO, He got a bath last week. ...me too!! Hehe.  ;D
FFS, I hope you didn't share the tub at the same time, Bill-
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Offline Bill/BentON Racing

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Re: Cobra motor disassembly and rebuild
« Reply #69 on: December 17, 2015, 10:29:20 PM »
They only numbered  for convenience and proper placement.  As in 1 would go on 1, 2 on 2. Then if disassembled easy to put back where they were. Kinda like marking a piston to reinstall. Same weight don't matter about no stamped dots, numbers etc.  But if removed,  no bearings changed you sure want them back on the journal they came off of. Carry on,   ;D....I'm an assembler! Round holes and square pegs, that be me!!! Lol., Bill
BentON Racing Website
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Over 35 years of experience working on vintage motorcycles, with a speciality in Honda SOHC/4 with a focus on the CB750 and other models as well from 1966 - 1985.
______________________________________
1993 HRC RS125 | 1984 NS400R | 1974 Honda CB750/836cc (Calendar Girl) | 1972 CB 500/550 Yoshi Kitted 590cc | 1965 Honda CB450 Black Bomber | 1972 Suzuki T350 | 1973 88cc | Z50/Falcons Pit Bike | 1967 CA100| 1974 CB350 (400F motor)...and more.
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Offline Retro Rocket

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Re: Cobra motor disassembly and rebuild
« Reply #70 on: December 18, 2015, 12:30:23 AM »
Stop avoiding the big question Bill, Did you have a tub with the dog or not !!!.... ;D :P ;)
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Offline johno

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Re: Cobra motor disassembly and rebuild
« Reply #71 on: December 18, 2015, 01:06:04 AM »
Centre popping the rod numbers on two halves is bad practice, if you decide to do it the rods must be resized after, if you find a set of rods done like that carefully check the big end for roundness with the rods torqued up to spec to make sure the person resized round again.
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Offline MRieck

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Re: Cobra motor disassembly and rebuild
« Reply #72 on: December 18, 2015, 04:31:13 AM »
They only numbered  for convenience and proper placement.  As in 1 would go on 1, 2 on 2. Then if disassembled easy to put back where they were. Kinda like marking a piston to reinstall. Same weight don't matter about no stamped dots, numbers etc.  But if removed,  no bearings changed you sure want them back on the journal they came off of. Carry on,   ;D....I'm an assembler! Round holes and square pegs, that be me!!! Lol., Bill
Bill.....I am absolutely sure they are not numbered for placement...... the dimples are to make sure the rod big end goes with the correct rod. It doesn't matter where you put the rod.
« Last Edit: December 18, 2015, 04:33:05 AM by MRieck »
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Offline Bill/BentON Racing

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Re: Cobra motor disassembly and rebuild
« Reply #73 on: December 18, 2015, 05:13:55 AM »
I agree, don't matter. You do it so big ends don't get mixed up. Nothing to do with measurements, just convenience. But still when new, I always put 1 on 1 , etc.  But yall right, rod and crank don't know,  like Frank first said if you're reusing them and the bearings then they need to go back where they came. That's why we always put 1 on 1 etc. Just made sense, Honda didn't number 1-4 for sure. So any rod can go on any of the rod journals I agree,  now the $64,000.00 question, no not with BabyFace,  but the real question is what pieces aim going to use. Thinking of the stroker crank on bottom pic with the RC  steel rods off of the middle crank in pics,  Bill
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Over 35 years of experience working on vintage motorcycles, with a speciality in Honda SOHC/4 with a focus on the CB750 and other models as well from 1966 - 1985.
______________________________________
1993 HRC RS125 | 1984 NS400R | 1974 Honda CB750/836cc (Calendar Girl) | 1972 CB 500/550 Yoshi Kitted 590cc | 1965 Honda CB450 Black Bomber | 1972 Suzuki T350 | 1973 88cc | Z50/Falcons Pit Bike | 1967 CA100| 1974 CB350 (400F motor)...and more.
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See our latest build 'Captain Marvel' CLICK HERE

Offline dragracer

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Re: Cobra motor disassembly and rebuild
« Reply #74 on: December 18, 2015, 08:10:58 AM »
Go big or stay at home!!! Screw a 10 second ticket, put the striker crank in there and run some 9's.

Just do it!! Oh, but put new bearings on the rods first. You'll be pulling the bottom end apart a lot for maintenance so at least start with a fresh set to begin with.