Won't start

[Kayla850]

Well a good inspection of the the valves and valve seats has lead me to the conclusion that a replacement head is the way forward.

Someone, at some time in the bikes history, has modified the the valves on a lathe. I have no idea what they hoped to achieve but they ruined all the inlet (not exhaust valves as I said) valves by badly (and I mean badly) turning their own profile on the valves which means there is no sealing surface between valves and head! The "land" that should be ground in to get a good seal is smaller in diameter than the valve seat diameter. Not content with this appalling modification some work was undertaken on on the inlet seats replicating the surface finish on the valves, a shocking seat recutting job. No chance of the surfaces mating.

Why did the compression show good when checked - totally in accurate compression gauge?

I am now looking for a new cylinder head!!!

Mang

It might be cheaper/easier to do a 600 conversion. Granted, it removes the whole point of owning a 400, but it'd get the bike up and running again in a very short time.

[Mang]

Kayla

Thanks for your comment its genuinely appreciated.

I have to start by saying I am totally pedantic about restorations which is why I bought the SP as it was pretty original. With the exception of the tailpiece it now looks like the day it left Yamaha (aside from some bandit ruining the head). I want a bog standard bike and that is where I intend ending up.

The 600 conversion crossed my mind but I have spent a king's ransom to get this far on originality and I don't want to deviate.

I have sent you a private email.

Thanks again for you comments.

Mang

[Evilchicken0]

That's a bugger - the valves could be slavaged from a 600 head but if it's the seats then the head itself is toast, so you'll need a 3TJ head which isn't so common.

[Mang]

I have taken the head to a mate that runs an performance vehicle engineering shop. He reckons he can recut the valves seats but it won't be cheap. I think it's worth doing, not based on any sort of commercial decision,but how much time and money I have spent to get this far.

My mate reckons the valves (INLET) are beyond repair so I need new ones. Evil you reckon that the 600 are the same as the 3TJ ? Is this true? If so what are the part numbers and are they commonly available.

Thanks for your help. Again!!

[Evilchicken0]

What I mean is buy a secondhand 600 head for the valves - If you're looking for genuine Yamaha parts them try to order through the SP part number but they really won't be cheap.
You can get a T'Cat for around £50 up

Check the Service manuals in the Document Libary (top of the page) they give the valve sizes for the 3TJ SP and the FZR600R ... you'll probably get some "free" spacer washers too

[Mang]

Evil
Looked up the specifications and dimensions of the 400 and 600 valves and they are different. Back to the drawing board on this one. Now scouring ebay world wide looking for inlet valves at a good price!

[ChowderV4]

This is not promising as i've pretty much got the exact same problem with my 3tj, i've checked everything apart from compression and clearances which are next to do, valve clearances we done recently though so its a bit of a mystery at the moment.

I'll be keeping an eye on this thread.

[Evilchicken0]

Chowder you might find that "they were done" can mean "they were going to be done"

[ChowderV4]

oh no they were definitely done, the bike was my brothers before and my dad did them last year.

[Evilchicken0]

Fair enough