Author Topic: Mystery - Gutless 400 four  (Read 300 times)

Offline Northy

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Mystery - Gutless 400 four
« on: December 04, 2018, 05:18:26 PM »
Ok Folks , brought a 400 from mate , never do that with recorded mileage of 9k (mot's  to back it up ) but he couldn't  get running right . I got running better but its gutless and has other issues.
Here the symptoms  :-
On start up smokes , but clears .
Pulls fine up to about 4.5 k then misses ,no power can rev it up to 8 k but feel like it missing on one pot, hot or cold
Not go above 60 !! feel like sock up the exhaust pipe
Using oil but once warm there no smoke or horrible noises
Oil is blacken within 200 miles
Compression 25psi lower than my other 400f on no's  1/2 same on 3/4 as comparison only.


So how you going through the thought process ...and coming to a conclusion but first this is what has been done, with no effect :- 
Swapped over Coils from running bike, carb sonic cleaned  checked x2  and then swapped over with another set , electronic removed back to points, new air clean and plugs, advance retard mechanism  checked 

However you I can hear shouting it the valve steam seals !! ...that covers the startup smoke and oil usage  agreed  so lets whip the head off have looks see. Expecting  broken rings as well 

First this head been of before ! and came  off to easy and the exhaust ports are very sooty

Umm  lots oil  so much the carbon comes off easy , note  one no.3  pot  is less oil and this confirmed by the colour of the plug
head


piston tops



So next was to remove the barrel , expect a ring to fall out ...hope all in one piece and then notice the are piston 0.5  O/S.


Bore with honing marking in place



So there looks to nothing to much wrong with piston / rings and quick check on the ring show all OK  and no slop in  bores .... could have been rebored wrong ?

OK move back to valves and just whipped one out  and it clear the valve stem seal are shot  see pictures but also note the perfect face on the valve  (plus loads of oil)   





So OK stem seals can account for oil on start up, oil usage,oil in bores (?)  but it would still run Ok and given that there no oil appears to burning pass the pistons.

However I cant see that the seals would have such a dramatic  effect on the power of the engine . Ok it can suck in oil and air and weaken the mixture but never this bad or has the thing not run in yet ?         

Tomorrow I will check the bore/piston and all the valves 

So what am I missing (apart from few brain cells !!)



   







   
« Last Edit: December 04, 2018, 05:32:23 PM by Northy »
How many is too many bikes ..... when you have no space left.

Offline Nurse Julie

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Re: Mystery - Gutless 400 four
« Reply #1 on: December 04, 2018, 05:39:33 PM »
Valve stem seals, as you say, plus an air leak somewhere. The engine has had a hard 9k miles if it's already needed are re bore to +.50 Is there oil vapour in the air box?.
Im a Nurse, trust me, this won't hurt.....much !!!

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Offline Nurse Julie

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Re: Mystery - Gutless 400 four
« Reply #2 on: December 04, 2018, 05:53:43 PM »
Just looking at the close up pictures of the barrels, the one on the right has got some huge gouges and marks on the bore which won't help much. Looks like it has had standing water damage in the past and someone has tried to clean it up, unsuccessfully.
« Last Edit: December 04, 2018, 05:56:46 PM by Nurse Julie »
Im a Nurse, trust me, this won't hurt.....much !!!

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Offline Northy

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Re: Mystery - Gutless 400 four
« Reply #3 on: December 04, 2018, 06:23:30 PM »
Think that's oil in bores or a reflection, there's no real marks other than honing marks and the brown ones at the top.  (just been outside to check) There's not even a lip you can feel at the top either, reckon they only been in there 500 miles or so. Another 400f engine I have ,had water/ seize marks so seen them before.
 
Very little oily vapour in air box , breather pipe  and cover on the rocker box very clean. its not blowing oil its sucking it in.

Story behind the bike is it was in shop window , however I reckon its was raided for spares. So it could have seized whilst sitting there  or this might not be the right engine so I'll take the 9  k with pinch of salt. The cam is good and bearing in the head are Ok  ie relate to 9 k  not  109  :-) 
 

How many is too many bikes ..... when you have no space left.

Offline Nurse Julie

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Re: Mystery - Gutless 400 four
« Reply #4 on: December 04, 2018, 06:36:14 PM »
So these marks are oil ? Look like holes and gouges to me but good if it is only oil.

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Offline Northy

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Re: Mystery - Gutless 400 four
« Reply #5 on: December 04, 2018, 06:50:20 PM »
Yes  that's oil here's a  better picture ,  cleaned up ....nothing much to worry about apart the honing marks should be criss cross  pattern


How many is too many bikes ..... when you have no space left.

Offline Nurse Julie

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Re: Mystery - Gutless 400 four
« Reply #6 on: December 04, 2018, 06:56:04 PM »
Yes, I was thinking nit much X hatching had gone on there 😀😀
Im a Nurse, trust me, this won't hurt.....much !!!

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Offline TrickyMicky

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Re: Mystery - Gutless 400 four
« Reply #7 on: December 04, 2018, 09:37:46 PM »
Don't go much on the finish of the honing, plus it might be worth checking that the piston rings have been fitted the right way up? Regards, Mick.

Offline Bryanj

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Re: Mystery - Gutless 400 four
« Reply #8 on: December 04, 2018, 09:41:44 PM »
Piston to bore clearance?

Offline Trigger

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Re: Mystery - Gutless 400 four
« Reply #9 on: December 04, 2018, 09:53:17 PM »
Honing too coarse which has already damaged the rings and a good cross hatch is needed if the piston to bore clearance is with in spec  ;) 

Offline Clem2112

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Re: Mystery - Gutless 400 four
« Reply #10 on: December 05, 2018, 03:14:53 PM »
There I was hoping the culprit would be discovered and I could cure my gutless engine.
But those marks in the bores look very wrong as others note and tell me the compression will be down.
Hoping to find that its been the valve seats all along with mine.

Offline hairygit

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Re: Mystery - Gutless 400 four
« Reply #11 on: December 05, 2018, 03:29:24 PM »
Honing too coarse which has already damaged the rings and a good cross hatch is needed if the piston to bore clearance is with in spec  ;)
  Not kidding there Trig, almost looks like someone has used a 60 grit flapwheel on the bores to save the cost of having then properly bored. :o :o :o :o :o :o
If it's got tits or wheels, it's hassle, if it's got both, RUN!!!

Offline Northy

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Re: Mystery - Gutless 400 four
« Reply #12 on: December 05, 2018, 05:14:13 PM »
Ok folks  ..here we go

Checked the bore / piston / ring gap no issues there.
Bore honing is not as course as picture makes out (reflecting alot from the flash) and I've  given them and quick whiz with honer (not a homer) and all OK there. See picture a can lie.

However have found the reason for no power ,importantly the cause and things that don't help matters  :-(

Exhaust valves  from 1 & 2  ( 2  blowing badly)



The head ,and the scratch marks where already there , umm
 

Another issue is the valve seats appear to too wide, spec is  1.5 mm

On on the head we find that where the bonded washer sits the ally been domed / squashed , Both of them.

 

How that's happen I don't know but I will get milled flat and already have some new bonded washers.

No play in valve / guides , One shim missing from under valve spring,all spring well within spec.

So logically thinking, the valve stem seal have given up the ghost - having not been replace at the time of the rebore (although softish the holes are enlarged). This mean the engine is sucking in oil, burning it leaving lots of carbon on the valve etc (there in way!). The seats being too wide allow carbon to form on them  . The valve seat blow then mean no compression , poor mixture
   = NO POWER   :o

Does that  sound right ?  at least its not an expensive fix.


BTW spend most of afternoon removing the remains of the base gasket which had been stuck on with some grey cement the like of which I've not seen before , Why ? .             




 

 

How many is too many bikes ..... when you have no space left.

Offline Nurse Julie

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Re: Mystery - Gutless 400 four
« Reply #13 on: December 05, 2018, 05:32:42 PM »
Quote
'BTW spend most of afternoon removing the remains of the base gasket which had been stuck on with some grey cement the like of which I've not seen before , Why ? .             

Because whoever did all the work previously was a muppet. That is appalling work all round. They should be shot. Just my opinion.
Im a Nurse, trust me, this won't hurt.....much !!!

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
http://www.sohc.co.uk/index.php/topic,14049.msg112691/topicseen.html#new

Offline Northy

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Re: Mystery - Gutless 400 four
« Reply #14 on: December 05, 2018, 08:22:20 PM »
Agree some muppet been there before ..wasn't my mate ...he would given me the engine to work on. Spoke to him (mate) and we  think we have our suspicions it was done by the BMW car dealer were it spend most of it life or handed out for someone to fix up.
But hey who care's now , its should be sorted and back on road in no time ....... then I'll get back to building the special one.


OH Clem2112  might give you a few pointers ,best check you compression first. ...... and don't let muppets lose in garage with spanner.
How many is too many bikes ..... when you have no space left.