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OAP Ted's CB400F2 rebuild - engine not run for about 12 years.

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McCabe-Thiele (Ted):

--- Quote from: THUNDERDOWNUNDER on November 07, 2020, 07:28:12 AM ---Hi , have you got a picture of the underside of side cover where the electrics are ? My 75 400/4  doesn’t want to close so just need pic to see what’s the right and wrong way to wire up things . Thanks if you can .

--- End quote ---

Does this help ?
IMG_20201107_111052 by Teddy Bagshaw, on Flickr

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McCabe-Thiele (Ted):
Bit of an update on the project.
When I first started the engine after it's 12 year rest it started pretty easily this has in part led me to believe that maybe an engine strip down was not needed. (Clearly in denial here)

Since that first start up it has taken a lot of more cranking to get her to fire up - this has led me to suspect that the compressions are not that brilliant. A cold check on 25th Sept 2020 revealed that the compressions were a pretty even 90 psi on all cylinders rising to 110 psi when check some days later.

Yesterday I just could not get the engine to start so this morning I squirted some 2T oil in all four cylinders with a view to re-checking both cold and hot compressions. The first thing I noticed was that when I cranked the engine about an hour later without the plugs in place almost no oil was pushed out so it had obviously drained through the piston rings I am thinking. Another cold check then revealed 205 psi on cylinder 4 I didn't bother check any others I knew the truth already.

When I replaced the plugs the engine fired up fairly easily so I let her run until up to temperature then did a hot check on cylinder 4 - it was only 120 psi. Clearly I am loosing compression with the rings / pistons being the main culprit.

Obviously I will need to carry out an engine strip as the compressions are well below par. Just as a point in case the engine does run quite nicely in the circumstances especially considering that I have not adjusted any idle air screws.

I now intend to crack on with the strip down of the frame ASAP hopefully I will get the engine out before my operation that still has no date due in part to the effects of Covid on ICU bed availability.

Just for the craic I have recorded some engine running earlier today to keep me enthusiastic I will post a link shortly.

https://youtu.be/SWwb3LgNpIY

McCabe-Thiele (Ted):
Could not resist a bit of revving - smoke is a mixture of 2T oil burn off and hot oil spilt on the engine. It will be next year now before she runs again (hopefully).



https://youtu.be/3CpAYjNHggI

smoothoperator:
Are you sure about the 205 psi on No 4 Ted. I know what you mean about a successful engine run making you overly optimistic. Had my engine running 3 times now and started to think I'll leave the carbs alone it's running great. Last run petrol was pissing out from No4 overflow pipe. However I didn't use your bike rocking technique on this occasion. Anyways clearly the carbs WILL need attention. Good luck with the fun part of moving from fiddling about to taking to bits!

McCabe-Thiele (Ted):
Clearly the 205 psi reading is unlikely to be accurate. The gauge was less than £12 so it's a relative rather than absolute.

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