warped cylinder head

[jumjum01]

Just bought this rd350 Y3 cylinder head on ebay with the description "good". I am not sure thats correct, it seems warped. I had to shim 0.15mm left and 0.20mm right side to stop the straight edge from rocking. Guess this needs to be milled to seal correctly??

[Arrow]

Just be sure to check using the other side of the rule as well.

[jumjum01]

Same result on both sides, rocks on flat table as well

[MK]

So what? You're gonna reshape the combustion chamber anyway, if you're after a decent compression ratio. One additional pass over the sealing surface doesn't add significant costs...

[jumjum01]

Yes you are right.. Contacted the selller and got 25% refund due to the warping.
Can I use 0,5mm copper head gasket without leaks?
I did a top speed run the other day and destroyed leftside piston at 160 km/h and it locked the motor up. Can this be caused by running BR8ES plug at high load?
Recent dyno run confirmed AFR to be 13:1 at WOT

[MK]

A BR8 is too hot for any extended period of WOT operation. Use 9 and you're fine.

Also an AFR of 13 may be good for performance but remember that fuel is also used for cooling. I run something like 12-12.5 in the WOT and high rpm range.
Check EGT to stay on the safe side.

But your piston does not look like the typical plug or EGT caused meltdown. This usually starts in the piston center slightly shifted to the exhaust side.
Not on one side like yours. This could be a lack of oil which is especially present with oil pump setups when you go fast, but not WOT.
For that reason I run premix of 1:40 to 1:33.

[kpke]

Can I use 0,5mm copper head gasket without leaks?

Below is my experience with a copperhead gasket. Good luck.

RZ350 RZ FZ FZR Project Ep13 Copper Head Gasket (Failed) Removal

https://youtu.be/F4BXM4nLlGc

And then fixing it

RZ350 RZ FZ FZR Project Ep14 Yamaha Head Gasket Install and a Short Ride

https://youtu.be/MFZsvpgaYh0

[kobra]

Use an OEM MLS gasket.

Do not run the BR8. Blew up my motor using one of those too. No ill effects from running a BR9.

You can mill the head but also the bolts will probably pull it straight.

[(F5)]

I wouldn't usually question mk, but I've had lack of lubrication (through a seal moving and diverting the oil into the crankcase). Looked much uglier on the skirt through abrasion.

The strange one sided effect I cant explain, but that clearly looks like detonation. It's been a very long time since I've seen a std head but I thought they had much more of a step than that. Likely been milled before? I'd check your head volume. I suspect it is too high, perhaps in relation to your petrol.

In NZ in the 90s we went to unleaded and my lightly tuned RZ melted a piston at high speed. Took some com out of the head to cope.

[jumjum01]

I took 2 extra pictures of left piston. One could argue that it started in the center and went towards exhaust port. I just measured squish with oem gasket and stock Y2 head installed. Its 1,46mm. I also measured the Y2 head cc to around 20ml and Y3 head to 21,5ml with a drugstore syringe and red coolant. I dont have the Y3 head at home right now to bolt on one cylinder and measure squish, its at work and I am at home with fuc...g covid

[MK]

I'll revise the "low on oil" hypothesis, too, after having seen the piston crown.
This clearly cries too hot plug.

[(F5)]

Too hot plug would certainly exacerbate the situation. That looks exactly like mine (running 9 plugs) when they changed the petrol on us to some rubbish, I think we got a dreadful first batch of unleaded circa 1991. Ideally you should measure the volume on the engine so you can get the real (full stroke) ratio and see if it is too high. What kind of petrol do you have, wherever it is you are located? And do they use Mon or Ron octane rating? Ethanol content?

[RZtuner]

Nope, not the plug, burning the exhaust side like that is classic lean... either an air leak on the intake side or too lean on the Main Jet. My guess would be the MJ if the motor has been built properly and pressure tested.

As far as the warped head, I finish all my heads by lapping them flat on a machinists surface plate, it's the only way to ensure they are perfectly flat. You can make a cheapie surface plate out of a square of float glass.

Stay away from those copper head gaskets, the OEM head gasket is the best choice.

[jumjum01]

Ok guys, thanks for all your input. I run fuel injection with R6 TBs, so adding a little extra fuel near and at WOT i easy to be on the safe side and avoid lean conditing. And then change to BR9 plugs. I live in Denmark/europe and we use ron ratings. I mostly used 100 actane since it only has 5% ethanol and less chance of sucking up moisture and corode the fuel tank. I was hoping at just hone til left cylinder and install new prox piston, but by placing a new piston ring in the bore I could see a small light between ring and cylinder wall. So the bore is not perfectly round. Also the prox piston is 12 grams ligther than OEM although they claim to be made to OEM specs. Guess I will have to send boths cylinders out for boring and install new oversize pistons. Did a compression test on cold engine, left 100psi, right 110psi

[RZtuner]

Do a plug chop with the BR8s to see if they are the correct heat range for your engine before stepping up to a BR9. I have run BR8s at Bonneville in my RZs many times, 3 miles at WOT, no detonation, no exploding engines.

Learn how to read the plug properly, like jetting, you need to give the engine what it needs not what someone says on the internet. The worst mistake people make is fitting a colder plug and then leaning out the jetting to clean up the plug, that is a great recipe for detonation.