Burnt valve?

Thanks Kray, Swest. I am gonna have to really take it from the ground up. I'll firstly check the clearances and if they're ok take the head off. One thing I meant to ask is when doing a compression test number 2 stays at 125psi until I release the the pressure. That is in no way a form of leak test is it?

You have to give it time and see how long it takes to loose pressure. Then do all four and compare IMHO

JoHNy,

Just a run down of the basics, on the outside chance you don't know about this already.

A compression tester has the pressure release valve near the gauge - you must press it after every test to re-set.

A leak down tester pressurizes the cylinder with an outside source of compressed air, and the standard test is to calculate the percentage of that pressure lost over a specific time.

The only time I do the percentage calculation is when I'm dealing with an engine I want to buy sight unseen (long distance), or if someone wants me to give them the percent leakage numbers - say for a racing engine to track its condition over time compared to performance loss.

If I'm trying to find a fault, I rely on simply pressurizing the cylinder with a constant regulated air pressure between 90 and 100 psi at both TDC and BDC and listening and / or checking with soapy water for where the leaks are coming from - that is a lot more informative than knowing how much percent of air is escaping when trying to find out what the problem is and what needs to be repaired...

In most cases the head has to come off for any repair, at minimum, but at least you will have a much better idea of what needs to be done after that - valve grind, gaskets, rings, etc....

Kray-Z wrote: JoHNy,

Just a run down of the basics, on the outside chance you don't know about this already.

If I'm trying to find a fault, I rely on simply pressurizing the cylinder with a constant regulated air pressure between 90 and 100 psi at both TDC and BDC and listening and / or checking with soapy water for where the leaks are coming from - that is a lot more informative than knowing how much percent of air is escaping when trying to find out what the problem is and what needs to be repaired...

.

I'm mystified as to what testing at BDC would tell you? You're going to have a valve open either way....

Hello Larry! - still haven't run that exquisitely ported, big valve dual plug head you did two years ago for my big block J yet....my damned arms keep wanting to fall off of my shoulders...delays, delays! Maybe by this spring.....I'll be posting that build step by step.

Yes, I should have completed the memory lane trip and said....both valves obviously have to be closed for any pressure test.

At BDC....It tests for cracks in the cylinder wall - remember that I come from professional automotive / heavy equipment work, and most things I learned applied while doing that. Still applies mostly to liquid cooled bike engines or hard surfaced aluminum cylinders without sleeves like Nikasil....

I have done leak tests at BDC on engines - it is coming back to me now - loosen the rocker arm adjusting screws or take out the push rods or cams!

Lots of serious non -stock block V-8 racing engines used siamesed bore blocks - bored as big as 4.600" on the BB Chevy and even larger on the 385 series Ford. Just an added note - to get an idea of how much bigger that is than stock - when our first Brodix Chevy block arrived, I was amazed that I could take a short skirt standard bore 454 slipper piston and SPIN IT AROUND inside the cylinders of that 4.600" bore block. So little iron was left in between cylinders that hairline cracks would develop between two side by side cylinders ....one piston is squeezing into the one next to it trying to suck, bang, or blow... :laugh:

Big diesel V-8's like Cat's 3208's and some sixes with steel sleeves (wet liners) would crack the cylinders or sleeves near the middle of the water jacket....open the rad cap and listen for air (empty the rad / coolant first)....

I just remembered one of the many jokes at the truck (mostly diesel) shop I worked at once. Us mechanics liked toying with some of the drivers that would "hover" while we worked on their rigs. During the leak test (pull an injector) they would ask what we were doing when running air hoses into the cylinders...."inflating the engine to the correct pressure, obviously!" :evil:

Thank you so much everybody for all your suggestions and help, thank you.

Got to the bottom of it in the end. It was number 2 out of spec exhaust valve. Re-shimmed it last night, fired her up and it's now running like a dream. Simple as that. One thing I've learnt is how vital correct valve gaps are

Hey, at least it was cheap! :woohoo:

Hahahaha, indeed Kray, thanks for all your help mate

FWIW

The only 2 valve KZ streetbikes I have ever seen valve abnormal seat problems with have been some 750 engines. I have seen those seats chipped so badly that they did need replacing. Intake valves with the 45 degree face caving in isn't uncommon.

I have seen some GPz11 heads that were run really hard in drag bikes with serious cams and whipped springs where the seats chipped as well.

Any of the new 4 valve motors are potential seat problem engines. 900 Ninjas were really prone to chipped seats.