tapping

[Scotch10]

Hi I have a 1979 honda cb125t2. I have just replaced pistons, rings and put a brand new old stock cylinder head on. The head is built up with new valves springs seats and seals. I have put old camshaft, rockers, and camshaft holders back on but replaced tappet adjust screws. After all this I'm getting a tapping noise definitely from the head. Valve clearances double checked and set according to haynes,timing chain, guide and tensioner checked and are fine, valve timing double checked and fine, the head is correctly torqued.The tapping was not there before. Could it be the old camshaft bedding in to the new cylinder head otherwise I am at a loss. Any help greatly appreciated.

[bikenut]

Check if piston crowns are "contacting" the head...to rule that out.

If you cleaned the piston crowns, look down plug holes and look for " clean" ring mark on piston crown edge...if piston crowns not clean, look for clean ring mark on piston edge...
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nuts about bikes

[Scotch10]

[Islander]

Check your exhaust headers for leaks.

[MCN]

Only way for pistons to clatter the head is:
Worn big ends. (Piston connecting rod to crankshaft bearings)
Worn small ends. (Piston rod to piston bearings)
Massive layer of combustion deposits on crown/head.

I'd rule out the zost manifold leaks 1st.

We had a cnut put a main engine off-line for 10 weeks until a brand new cylinder head could be slow-boated into a rig in Iran.
Uncle MCS checked the Zost gaskets on that head. No gasket to be found.
New gasket fitted. Tappy noise now missing.

New head kept as spare.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[A100man]

[stinkwheel]

Are those heads not line-bored? So the camshaft caps go with the head? Many 70's and 80's jap bikes were.

Like A100man, my guess would be excessive play on the cam, only way to find out is to measure it with plastiguage.

Other classic small honda twin thing is loose camchain. The CCT spring isn't really strong enough to properly tension it in many cases. The done thing used to be to loosen the adjuster nut then nip it up again while pushing down on the tensioner slightly.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[jeffyjeff]

[Scotch10]

[Scotch10]

[bikenut]

You know of CMSNL ?

I though these have " cam shaft bushes" that the cam bearing surfaces, the outer ends, run in ?

Check CMSNL to see if they are still available...

A picture of the cam area might be good....
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nuts about bikes

[stinkwheel]

[Scotch10]

[jeffyjeff]

Wonder if the old valve covers on the new head fit in such a way that the rockers are striking the valve covers? Could try running the engine sans valve covers. Tent a shop rag over the head to catch oil splatter.
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History shows again and again how nature points out the folly of men - BOC

[Scotch10]