CB400F Frustrations - Not firing, low compression (Cyl Block now off)

[tom400f]

@ManicGTI I am in N1 and would be happy to help if I can be of any.

[ManicGTI]

Coincidentally I'll be moving to N1 (near canonbury) in June.

[Bodd]

I tried sending the pdf's to your email ManicGTI but your email client keeps returning them saying the account isn't set to receive attachments so I have uploaded them to my website, if anyone else wants them too you can download them from the link below, there are 3 files in the zip all in pdf format, they include the Parts manual and 2 supplements.

Download

[ManicGTI]

Download link works perfectly thanks, strange that gmail won't take it!

[ManicGTI]

After all your helpful comments I still haven't had a chance to take a look at it...I will get there!

[ManicGTI]

Well, after a hiatus from the bike I've managed to get outside and spend some more time on it.

Compression isn't looking good at all.

Dry Compression: 105, 0(!), 125, 110.
Wet: >200, 5(!),  ~160, >200.

I did three of them with some oil and they increased massively, with the exception of the second which blipped only a little.

So I'm assuming from this that I have a major issue on Cyl 2 (Where cyl  1 is the 'choke' end), Ring, piston or knackered valve/seat?

From my trawls across the web, It should still be 'attempting' to start given the pressures above (with exception of cyl 2!), even if they are less than ideal.  So I think I need to take a look at the carbs again.

I have to admit I'm starting to regret taking on a bike like this now, I just haven't had the time to give it he attention it needs :/

[tom400f]

Are you getting the bike up to Canonbury soon? We can get together, draw in our breath and rub our chins over it...

[ManicGTI]

So happily I've now moved to Canonbury...Sadly however the bike and all my tools are now in a garage in Hertfordshire as I don't have the room for two bikes here.  If you see an Orange Street Triple R around say hi, that's me!

I'll have to sort a trip up there at some point to do some more detailed diagnosis.  I was very close to buying a replacement engine from bikepusher but decided there's no real loss in tearing down what I have before I do anything silly.  Head off first to inspect the valves, then poss the cylinder block off for further inspection.  Down the rabbit hole...

[tom400f]

Head and barrels off is easy on this bike and will tell you a lot. Out of interest whereabouts in Hertfordshire?

[ManicGTI]

It's up in Cuffley, my Sister is living there and has an empty garage, well it was empty...now it's full of my stuff!

[tom400f]

Well at least the garage is being put to good use 

I can get there fairly easily if you ever want a second opinion... my bikes are in Southgate Road btw

Cheers
Tom

[ManicGTI]

Haha!  Now I'm really sad I don't have the CB down with me...I'm only just up on Mildmay Park Rd.  Thanks for the offer, appreciated, practically I think it'll be a few weeks until I can get up there to have a look anyway.

[ManicGTI]

So some progress!  Good and bad news, pulled the head and cylinder block yesterday.

- Exhaust Valve on cylinder 3 has as chunk missing, so that's the source of the low compression.  Tempted to clean it up, get a replacement Valve and lap the valves back in rather than a full rebuild.



- Piston on Cylinder 1 had a broken ring which seems to have damaged the Ringland, so it'll need 'at least' one piston.



All the pistons are Honda marked, and none of them have markings on the crown to show oversize.  There's some marks on the outside of them, and a few length ways marks in the bores.  Nothing I can feel with my nail though.

I've taken images of all the pistons:  https://drive.google.com/folderview?id=0B3qBPnS1cCGlNktETm9xbXNRN00&usp=sharing

Any views would be appreciated, advice on checking that they're in spec?

Does anyone know of an engine place in London (Pref NE or SW) that could take a look at my cylinder block and pistons before I decide where to go next? 

If I get it honed would I need to change all pistons and rings?

[Trigger]

Any skimping on a engine will bite you back later. What is the cam shaft like ?

[Bryanj]

From what i can see that is a set of exhaust valves not just one, replacing just one piston along with 4 sets of rings is a mimimum but a full set is better and as oversize cost the same as standard why not rebore if you can see marks, just my opinion its your money to spend how you wish