Coke Head!

[rogerowen]

Got a bit bored with chasing electrical faults and thought I might pop the rocker cover off to see what lies within after a 15 year slumber....Yikes! Not seen as much coke as this since I decoked a moped when I was 16!

Crankcase breather has been in the ultrasonic cleaner for 2 hours +, huge amounts of flakey coke in the rocker cover and over the top of the head. And, at the moment I cannot discern any valve clearance anywhere - could be the cause of so much carbon deposit???

I know that one valve is a bit sticky under load - (Nice Back-Fire)!

I have reasonable compression - 150 psi on 1,3 and 4 and down to 115 on 2 (which is probably were the sticking valve is).

Head rebuild scheduled for Winter months fun. Rimmer seem to do a reasonably priced kit, and local engineer has quoted £90 + VAT to replace valve guides and cut seats.

Just wondering what the inside of the sump is like - another winter job methinks.

  

[Geko]

Why don’t you try decoking with water through the carbs and take a compression test thereafter ? You may be positively surprised with the result and may not need to take the head off afterwards 

[Waldi]

The coke you find is made by condensed vapours. The vapours (leaking combustibles) become liquid at colder area’s in the engine, which the rocker valve obviously is. I suggest to inspect and clean the breather system. Other (and likely) causes are worn piston rings and valve guides.

Most likely there will be some coke and gunk in the sump too, that has fallen down. Once you do the head, I would take the sump off for cleaning and inspection of bearings and then decide what to do next. If the engine is running well, you may be tempted to leave.

Waldi

Edited August 11, 2019 by Waldi
Typo’s

[rogerowen]

Thanks. Yes, cleaned the crankcase breather and engine running noticeably better. Head rebuild in the pipeline, and a good sump clean on my list.