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Post by Ihaveadream on Jan 17, 2023 17:42:28 GMT
My new to me 1978 CB250n needs a new balance chain, so out comes the motor.
The cam chain is ok, but the oil pump chain is toast .
Odometer shows 42k , so as someone has been into both side cases, and spent a lot of money on her, they either did not know about the balance chain shelf life , or ignored it. , It has been a long time since I rebuilt an engine , so this will be a labour of love which I shall enjoy. There is really good compression when I kicked her over, but I shall clean the valve seats
anyway, and fit new stem seals.
I have the carbs off, which is a faff, had to move the air box back to allow removal. Thanks to a guy on you-tube for that info..
Rant time Mr Honda/
Why would you design an engine that has such a puny chain to drive the balancers, giving owners the delight of stripping the engine to change it.
Photos to follow later .
Bob
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Post by johnjones on Jan 17, 2023 23:18:31 GMT
Your heading for a real education, let's just hope you don't have to change your name to " I have a nightmare "...fingers crossed.
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Post by Ihaveadream on Jan 18, 2023 10:13:08 GMT
Hi John. This is more a hobby bike than a must get on the road and ride it. My R1200RT is my main bike so time is not an issue . I do have a modicum of skills with engines which will help. The bores will be measured for wear, and as I purchased the bike really cheap spending some money on her is not a problem. Lots of parts have been stove enameled, so I have to decide whether to strip it and have the frame done too, or leave it as is. The frame is not rusty, but has been badly coated as some point. I have never completely stripped a bike before, therefore, I am very tempted to go the whole hog now my garage has been sorted I have the space . My first question concerns the carbs, what is the best way to drain all the residual fuel? Do I removed the bowls and use a little compressed air them ? Bob
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Post by BritPete on Jan 18, 2023 10:15:57 GMT
Those carbs look clean!
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Post by johnjones on Jan 18, 2023 13:55:45 GMT
They do look very clean, Allan bolt float screws as well, also new Idle screws/needles, but, as well all know, never judge a book by it's cover....
You have a manual and know of CMSNL for the exploded views...
Have your heard the engine running ?
As to carbs, yes, remove float bowls, clean in there like the outside ?
I would want to soak carbs in oily petrol for a day then bag until ready to refit. Clean just before refitting.
Pictures...
You have a flywheel extracted bolt and clutch peg spanner ?
Banana boxes are free.
You are aware of the sometimes very problematic head bolts ?
Take your time, be methodical and enjoy.
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Post by Ihaveadream on Jan 18, 2023 17:18:44 GMT
The engine started straight away , very smooth so no obvious carb issues, only idle was low. oily petrol? what ratio is best. I am guessing soak, then drain and bag? I will take the bowls off anyway . The tools I have not thought about yet, just removing the wiring. deep joy.. I photograph everything.. especially wiring . Should there be a cover on the back of the headlamp. Mine has access all areas. The trip reset wheel spindle is broken, which I will need as there is no fuel gauge. What is the best way to remove the engine without drama. I would like to get it on the bench soon. Also best way to replace it , with a nice shiny frame . The rear sprocket has a lot of movement , pushing and pulling towards the hub, this cannot be normal surely. Apart from the engine, and some cosmetics, the sprocket and the worn center stand are the only other areas that need work. Bob
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Post by Ihaveadream on Jan 18, 2023 17:21:05 GMT
I forgot ask about the problematical head bolts.
Please enlighten me
Bob
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Post by Ihaveadream on Jan 18, 2023 17:27:30 GMT
Quote
yes it right the old superdream from 78 to 79
had the bolt with oils seals on 2 blots
as i have a cb400t-e from 79 that has them
if u do not put them in the right cylinder block then it will leak
oil
u can see where they go if u put a light down the block
and u can still get them
and they go on the right side of the block
hope that help u out
and if u manual is for superdream 1978 to 1984 then its on page 116
is this the issue.
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Post by BritPete on Jan 18, 2023 17:39:42 GMT
Headlamp looks to be correct but wiring should clip into mounts in the headlight case that are part of the mounting nuts Removal of engine depends on if the bolts are ceased - my view is get all the bolts loose and removable or cut them off if not Build a small trolley on wheels and place under the engine then drop the engine onto it and wheel it out
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Post by Ihaveadream on Jan 18, 2023 18:01:01 GMT
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Post by BritPete on Jan 18, 2023 18:25:24 GMT
This explains about the wrap on the engine - the next page shows the rebuild of the frame on the trolley
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Post by johnfcbn44dx on Jan 18, 2023 22:52:41 GMT
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Post by buster on Jan 19, 2023 8:48:52 GMT
those cylinder bolts can be quite difficult to find for the 250's, another solution is to get the two little notches in the base gasket face of the barrels filled in with aluminium weld and very carefully file them back flat
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Post by BritPete on Jan 19, 2023 13:39:52 GMT
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Post by Ihaveadream on Jan 19, 2023 20:55:43 GMT
Thanks John,
I will check my engine numbers.
Buster, can you elaborate on that please, photos ?
Britpete, thanks for the link I will have a look
Bob
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