Author Topic: Honda CB516 Cafe  (Read 5988 times)

Offline Mace53

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Re: Honda CB516 Cafe
« Reply #45 on: September 21, 2017, 03:56:02 PM »
Hey guys

After over 20 years sat rusting and feeling sorry for herself, I have finally got the old girl started! Very chuffed.

She runs really well, and sounds great with the 4 to 4 drag exhaust I made up.



Carbs are all synced and work great together.
She fires up straight off the kick even on a cold start.

 

However, I didn't think that my first engine rebuild would go smoothly and I do have a problem which im struggling to figure out.

The #1 cylinder is smoking quite a bit but only one the bike is fully warmed up. Nothing on cold idle or light revving from cold. Its a combination of blue and grey smoke and is definitely an issue.

Compression tests across all 4 cylinders :
1- 150
2- 155
3 - 150
4 - 158

After 5 mins of idle and revving these pictures are what I discovered:

Still image from a video I took.


End of the exhaust.


Exhaust valve.


Wet oil from the exhaust hole.


But the spark plug looks ok?






I've been reading reading checking and struggling to figure out what the primary cause may be.
 I'm running the carbs lean on 3 turns out due to the pods and 4-4 exhaust.

The previous topics on here point to leaking oil around the piston rings and leaking oil from the valve stem seals. But both are brand new.

I'm running an electronic ignition with brand new dr8es ngk plugs and ngk caps and leads.

Any ideas at all?

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Offline Bryanj

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Re: Honda CB516 Cafe
« Reply #46 on: September 21, 2017, 03:57:54 PM »
Bad stem seal or cravked guide in my opinion

Offline Mace53

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Re: Honda CB516 Cafe
« Reply #47 on: September 21, 2017, 04:01:51 PM »
Cracked guide as in the guide it physically sits in?

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Offline Bryanj

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Re: Honda CB516 Cafe
« Reply #48 on: September 21, 2017, 04:03:10 PM »
Yup, if some one in the past has not been carefull when fitting the valve cover you can crack the guide below the seal

Offline Tomb

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Re: Honda CB516 Cafe
« Reply #49 on: September 21, 2017, 04:16:52 PM »
And if cracked guide or bad stem seal on exhaust valve your plug will look ok as you don't suck oil in the cylinder.

Check the actual valve stem where it sits in the guide within the exhaust port.
Tom
'73 CB550 with CB500 engine café racer
'62 CB77 Sprinter
'70 CD175
'78 CB550 with sidecar
'80 Z50R
And a load of old Yamaha 1100's

Offline Mace53

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Re: Honda CB516 Cafe
« Reply #50 on: September 21, 2017, 04:40:39 PM »
Ah that makes perfect sense. When you explain it like that the exhaust valve does sound like the culprit. Could it also be the inlet as well?
I might just redo the entirety of the exhaust valve, stem and guide, just to be safe.
Is it an easy job to change the guides yourself?

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Offline Tomb

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Re: Honda CB516 Cafe
« Reply #51 on: September 21, 2017, 04:58:41 PM »
If you're from an engineering or mechanical background and have the right tools - yep
Tom
'73 CB550 with CB500 engine café racer
'62 CB77 Sprinter
'70 CD175
'78 CB550 with sidecar
'80 Z50R
And a load of old Yamaha 1100's

Offline Mace53

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Re: Honda CB516 Cafe
« Reply #52 on: September 21, 2017, 05:52:42 PM »
I think I can manage that. Job for the weekend.

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Offline Trigger

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Re: Honda CB516 Cafe
« Reply #53 on: September 21, 2017, 07:17:59 PM »
Ah that makes perfect sense. When you explain it like that the exhaust valve does sound like the culprit. Could it also be the inlet as well?
I might just redo the entirety of the exhaust valve, stem and guide, just to be safe.
Is it an easy job to change the guides yourself?

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You need a fair bit of tooling and the seats need to be re ground as the heat you need to put valve guides in sometimes distorts the seat a little.

 

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