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1970 honda 750 Low compression

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Goldenoldy63

CB750 Enthusiast
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Souris,Manitoba,Canada
my 1970 honda has not run since 1982,so i started to give the bike a compression test,and the 2 outside cylinders were 50 lbs on one side and 100 on the other side.After taking the tappet covers off on the inside cylinders I discovered the nut and tappet are missing on the intake valve on cylinder 3.i assume the motor needs pulled
 
The 100psi is, of course, to be expected on a "stored" motor. The 50, obviously, represents issues; rusted cylinder or valve seat, etc.. The missing tappet - who knows.... To do it right, the top-end (at least) should come down and everything checked and refurbished.

It may be possible to get it running, as is, if the tappet is replaced, but it's an iffy proposition - lubricating rings, cleaning valve faces while assembled - slim chance that it would result in a reliable motor with proper performance and no leaks.
 
After sitting that long I would pull and tear down to look at it. With parts missing it was probably park because of an issue. You may just have a pile of parts with the engine unknown and the issue with no frame number. Depending on how good of condition and what your plans are on how you will build the bike.
 
Goldenoldy63 said:
my 1970 honda has not run since 1982,so i started to give the bike a compression test,and the 2 outside cylinders were 50 lbs on one side and 100 on the other side.After taking the tappet covers off on the inside cylinders I discovered the nut and tappet are missing on the intake valve on cylinder 3.i assume the motor needs pulled
Click to expand...
dirtdigger said:
After sitting that long I would pull and tear down to look at it. With parts missing it was probably park because of an issue. You may just have a pile of parts with the engine unknown and the issue with no frame number. Depending on how good of condition and what your plans are on how you will build the bike.
Click to expand...
Thank you for the input .i had planned on doing top end for sure,the bike itself is in overall very nice condition,being stored inside a garage. It did have a triumph windjammer and 6 inch over forktubes and a seat and very high backrest,but the exhaust is in incredible condition and should clean up nice.My plan is to restore to original condition.I did pick up a near mint condition seat years ago and it turns out it fits perfectly.Again thank you for the help.Rob
 
jpdevol said:
The 100psi is, of course, to be expected on a "stored" motor. The 50, obviously, represents issues; rusted cylinder or valve seat, etc.. The missing tappet - who knows.... To do it right, the top-end (at least) should come down and everything checked and refurbished.

It may be possible to get it running, as is, if the tappet is replaced, but it's an iffy proposition - lubricating rings, cleaning valve faces while assembled - slim chance that it would result in a reliable motor with proper performance and no leaks.
Click to expand...
Yes i do want to make it a reliable bike again so will definitely do the complete top end.thanks for the input
 

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Well looks like a good starting point. I would definitely do a stock style rebuild with that bike.
 
Goldenoldy63 said:
Dirtdigger.I drive right through black Hawk as we go down to sturgis on a yearly basis,the roads and scenery is incredible.we stay at bells motor inn, but it was closed last year.
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Nice! Glad you enjoy the area. I couldnt imagine living anywhere else. Would love to see this 750 running around the area when you get it done.
 
dirtdigger said:
Nice! Glad you enjoy the area. I couldnt imagine living anywhere else. Would love to see this 750 running around the area when you get it done.
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That would be awesome.I will probably ask a million questions in the meantime.Like i have 3 exhausts removed from bike but the fourth wont come off.tried a bit of heat but am a bit leary on putting to much heat. i have tried removing the two screws,got them both loose but still extremely hard to unscrew and dont want to strip the screw,Any suggestions.thanks rob
 
The exhaust should come off the spigot fairly easily so Im not sure whats going on. Once you get the finned clamp off, the exhaust is slotted and should be loose from the spigot that bolts to the head with those to screws you took out. With the spigot unbolted too, I dont understand why you cant just take the exhaust off the bike? I guess I can visualize what you have going on?
 
dirtdigger said:
The exhaust should come off the spigot fairly easily so Im not sure whats going on. Once you get the finned clamp off, the exhaust is slotted and should be loose from the spigot that bolts to the head with those to screws you took out. With the spigot unbolted too, I dont understand why you cant just take the exhaust off the bike? I guess I can visualize what you have going on?
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I dont have the screws totally off, just loosened,but prior to loosening screws i put heat to the area and lots of pressure and wont budge.the other 3 came off easy
 
It would be pretty hard to get the parts too hot as they are both steel, only thing would be discoloring the chrome on the pipes. I would bolt the spigot back on the head use some heat and try to twist the pipe free from the spigot. If you take the 2 screws out the whole thing will come off the motor but then you still have to get the spigot out of the exhaust pipe
 
dirtdigger said:
It would be pretty hard to get the parts too hot as they are both steel, only thing would be discoloring the chrome on the pipes. I would bolt the spigot back on the head use some heat and try to twist the pipe free from the spigot. If you take the 2 screws out the whole thing will come off the motor but then you still have to get the spigot out of the exhaust pipe
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Ok thanks thats what i started with the screws,and have them loosened but the one is very tight even though i have turned it several times
 
Goldenoldy63 said:
Ok thanks thats what i started with the screws,and have them loosened but the one is very tight even though i have turned it several times
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After heating up the screws a couple times ,was able to get the exhaust off with the spigot attached amd will try and get it off later.Now trying to remove motor removed a very tight fit.
 
You will need two people it is heavy and awkward. or strip completely down to the frame and engine, lay on its right side and lift the frame off the engine. Removing all the exhaust spigots does give you some more room for wiggling it out.
 
dirtdigger said:
After sitting that long I would pull and tear down to look at it. With parts missing it was probably park because of an issue. You may just have a pile of parts with the engine unknown and the issue with no frame number. Depending on how good of condition and what your plans are on how you will build the bike.
Click to expand...
After tearing apart the top end and cleaned everything.It it all looks pretty good and I’m putting things back together now. There was a fair bit of carbon everywhere, and the Pistons cleaned up very nice. I have installed new rings and that part went together well. I read about the heavy duty studs, but I’m gonna go with The ones that came with the bike, hope it doesn’t bite me in the ass as it was a pain in the ass to pull the motor. I am going to torque the head bolts a little bit tighter. And after giving the cylinders a light hone and checking the ring gap.it was well within the gap tolerances.i am ready to carry on with the top end,but takin a break as were off to cuba..have a great day. Rob
 

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