Valve status after lifting head

[Uboat]

HI,

I managed to lift the head of easily once I found the three front bolds that are not mentioned in the workshop manual!

So now I will clean the head. Can you motorheads tell me the status of my valves, as by the photo? I guess its normal to have some carbon on the valves. The inlet valves are all rather clean, but the exhaust side valves are all more worn.
What is your advice? I am not into racing, but I would like a decent engine. The engine has done 125000 kilometers with regular maintenance.

/Ulf

[AHM]

Ulf,

How thick are the shims?

Simon

[peterako]

Hi Ulf,

I'm no expert but if budget allows I'd replace all the valves, especially if there is any hint of doubt in your mind.

How thick are the shims at the moment?

Are the valve seats in good shape?

Very thin shims may indicate that seats are receeded and 'may' need replacing.

Finally, find a good, and realtively elderly, engine man and become friends

His knowledge will become priceless

Peter

[45bvtc]

But the valves in your photograph do not appear pocketed or recessed, I've seen a lot worse! So if the engine was running ok before the head was lifted, and the valve shims are in a usable thickness/condition (all above 0.070" say) then I'd:

1) De-coke the valves and seats (and valve throats/ports etc.)
2) Make sure the valves aren't bent: if they are then new valves and maybe guides are required
3) Make sure the valve seats aren't concave: if they are then carefully face off the seats or replace the valves
4) Make sure the valve seat inserts aren't 'gouged': if they are then carefully re-cut the seats
5) Carefully lap each valve to produce a thin but full seat (use engineers blue) on its respective valve insert.

To check the effectiveness of the valve-to-seat seal(s):
1) Fit the spark plug and tighten to seal
2) Fit the valves (no springs): make sure the valves and valve seats are clean and free of compound; grease, etc.
3) Build up a 5mm bund (use silicon sealant) around each combustion chamber
4) Make sure the head is supported level
5) Fill each combustion chamber with paraffin and check for leakage/paraffin loss.

Where leakage through the seat-seal is found then re-lap or reconsider the potential of new valves and/or seats.

Oh, and make sure there's not excessive play in the valve stem guide.

PS: I've been following this simple procedure for 40-years or more on lots of 1558 Twin Cams...

Good luck!

[Uboat]

Excuse my lack of knowledge, but how do I measure the shims and what dimensions should they show?

The valves are fine on the inlet and exhaused side, my only concern is the pitting facing the combustion chamber.

/Ulf

[gjz30075]

They don't look pitted. What you see is carbon buildup. A good soaking with carb cleaner and mild brushing should clean it off.

[rgh0]

I agree with the recommendations of 45bvtc ( type 45 with a big valve twin cam I presume !).

Only additional thing I would do if reusing the valves would be to inspect them carefully for any stem cracking just above the head. A die penetrant check kit is cheap and worth using on them

i would also check the clearances between the buckets and the bore they run in and the valve guides and stems. The bores wear into an hour glass shape so you need to check across the full length.

Target valve shims thickness in an engine if not doing a full valve reseat is normally in the 2mm to 3mm range (80 to 120 thou). you can go do to about 1.5mm (60 thou) but that is an absolute minimum. If putting in new valves and seats I would normally aim for around 3 to 3.5mm (120 to 140 thou) in a standard unmodified engine. The rest of the engine valve train specs and design affect this target clearance and if modifiying the cams, valves, springs etc you may aim for something different.

cheers
Rohan

[sutol45]

Rohan and 45bvtc are correct, stay on the path.

I have to say that 45bvtc rebuilt two of my 'tired' engines a few years ago and they've been faultless ever since.