Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: Pauarc on June 29, 2024, 10:00:25 AM
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Out last night all going okay then I could hear a hissing noise from the front of the engine look this morning blown a spark plug thread looks like I’ve got to take engine out not a great night any one use the spark plugs inserts where you re-tap it and put an insert in
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A few people have used these kits, cheap and easy to use. Make sure you use plenty of grease on the tap to trap as mucg swarf as possible whilst tapping the thread. Check the plug size and thread as well as there are a few kits out there.
https://www.ebay.co.uk/itm/264507390056?epid=6024255209&itmmeta=01J1HMKW8Z97DWPAGQ328T5H6W&hash=item3d95de7868:g:uZMAAOSwEJZjToA8&itmprp=enc%3AAQAJAAAA4KJAmHit8gk4yKYXbCnvy3fRue1wPZklwrEyEoSlO5o5aBIDae05IbiRx2ZrV3vO7xd4JtaIuXmAhm2zKFXy%2B6QFG1frkWmq7pO1nOzyuhCChDcX1YF6NYQuqhsssTlB33ArWYV7mvBvPCKxve7KVzTp0Dq3j%2FLhyquE3rlYFO%2B1XLcqePgSrgOptPfXXe%2FBINs%2FpfiGnWo3Rz9r5wY%2B8oCl0I305qx%2BYulxH8sGBiRpFlnXoFl%2FQ7l--EbhyyoP2iPCiQNAvouiPSENfMCJVYK0AbObKREy6MSkw4VSlRAd%7Ctkp%3ABk9SR8zEz7SMZA
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On a 750, can you just remove the head whilst the engine is in place in the frame?
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A local engineering firm used to do these when I was in the car trade. They did a mobile service to garages etc, more recently they withdrew the mobile facility as they were so overwhelmed with private customers restricting the mobile service for plant machinery only. They used some sort of suction process as well as grease to stop debris dropping inside the cylinder head.
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Which plug is it, if it is the inner plug then it would probably be better to do it engine out, unless your frame's had the modification to remove the section above the head you cannot take the head off in the frame.
Good luck.
Cheers
Dennis
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On a 750, can you just remove the head whilst the engine is in place in the frame?
No, it's an engine out job even to get the top breather cover off of the 750/4.
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Take it to a reputable bike engineer. An insert can be inserted with the engine in the frame (exhausts removed). With exhausts still fitted, it can be done but very, very awkward. Watch for swarf going down the hole.
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Trouble is, it’s number two cylinder and you can’t get straight onto it very easy
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Trouble is, it’s number two cylinder and you can’t get straight onto it very easy
You would be better off for piece of mind having all 4 done at the same time. It's 50+ year old alloy, if one has given way, it may not be long before the others give way.
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On a 750, can you just remove the head whilst the engine is in place in the frame?
No, it's an engine out job even to get the top breather cover off of the 750/4.
Thanks Julie
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Back in the 70's we used to do them in frame with helicoils BUT it was explained to customer it was at their risk as you may still have to remove the engine, only had to twice
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A few people have used these kits, cheap and easy to use. Make sure you use plenty of grease on the tap to trap as mucg swarf as possible whilst tapping the thread. Check the plug size and thread as well as there are a few kits out there.
https://www.ebay.co.uk/itm/264507390056?epid=6024255209&itmmeta=01J1HMKW8Z97DWPAGQ328T5H6W&hash=item3d95de7868:g:uZMAAOSwEJZjToA8&itmprp=enc%3AAQAJAAAA4KJAmHit8gk4yKYXbCnvy3fRue1wPZklwrEyEoSlO5o5aBIDae05IbiRx2ZrV3vO7xd4JtaIuXmAhm2zKFXy%2B6QFG1frkWmq7pO1nOzyuhCChDcX1YF6NYQuqhsssTlB33ArWYV7mvBvPCKxve7KVzTp0Dq3j%2FLhyquE3rlYFO%2B1XLcqePgSrgOptPfXXe%2FBINs%2FpfiGnWo3Rz9r5wY%2B8oCl0I305qx%2BYulxH8sGBiRpFlnXoFl%2FQ7l--EbhyyoP2iPCiQNAvouiPSENfMCJVYK0AbObKREy6MSkw4VSlRAd%7Ctkp%3ABk9SR8zEz7SMZA
The problem with this type of insert is the flange on the top. You need to rebate the face of the head so that this flange sits below the surface if not when you tighten the plug it with tighten up against this raised flange and there is every likelihood that as a result you will unscrew the insert when you remove the plug. If you are going to try and repair the thread in situ it may be best to use a helicoil as this will be fully below the surface? Best to get some expert advise before proceeding.
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The engine is ready to lift out then the head will be coming off to do the job will then see what needs to be done
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Yes I had a CD175 once with a flanged insert, it came out everytime I took the plug out, at the time it did not bother me but I'm a bit more fussy nowadays.
Cheers
Dennis
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Apply Studlock 270 just to the insert when you put it in it stops that happening.
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Quote from: Nurse Julie on June 29, 2024
No, it's an engine out job even to get the top breather cover off of the 750/4.
I can :o
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Engine back in bike and running just got to go for test run
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Well done. What did you use on the plug hole thread?
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Good work, and nice when you can get a problem competently sorted out like that.
Often viewed a s difficult to take these engine out as it seems a bigger task than necessary, but some modern bike and car are so much more difficult to access than these relatively simple era bikes.
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Used stud lock to hold the sleeve in place and help seal the thread
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👍
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Nice one - presumably you managed to do it without removing the cylinder head.
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No I strip the head off didn’t want to take the chance of getting any thing in barrels