Pinned So what have you done to your bike today?

A couple of weeks ago I realised one of the stanchion/caliper mounts on a ZXR250A had a crack in it. Annoyed by this revelation, I contacted my favourite spare parts provider and was further perplexed when young Chris told me he had zero forks for me.

Unperturbed by this disappointment, I contacted a number of local parts peddlers to see if anyone had a wrecked front end that I could steal the stanchions from. I’m told that this kind of cracking is becoming popular and that all forks are being snapped up to repair this kind of problem. If I want a fork it’ll be $150 or if I want both, a nice gentleman from Adelaide was keen for me to take his set for $250 plus $50 for postage. Hmmm…let me think about it.

eBay and gumtree here I come.

Fast forward, I find a ZXR250A being parted out and after contacting the seller, I’m told the forks are mint and I can have them for $140. I’m on my way. When I get there I find that not only are the forks still on said bike, but they are far from “mint”. Having travelled for over an hour to get to this obviously blind and slightly retarded individual, my mood is not positive. In the end, we agree to a compromise and for a little more than the price of a set of forks from Adelaide, I now have a rolling bike and an engine which “might” run.

If you’re still reading, then good for you. Here are the pictures of the stanchion before and after new stanchion was fitted. That’s one day of my life I’ll never get back!

 

No probs mate. They're getting thin on the ground down here too.

 

Oddly enough, it wasn't noticeable when riding it. But, all bolts and axle bolts were so tight I had to use a breaker bar to get them out!

 

They are pinch bolts, with the emphasis on the word pinch. IF you are not sure then when tightening bolts which are part of unusual assemblies you should refer to the manual for torque settings. Axles also are only supposed to be tightened to load the bearings the correct amount, when they are over tightened the bearing clearance becomes too tight creating more friction and a shortened life. All the fasteners on my Honda have been overtightened, if fact everything that has been touched is butchered.

 

Today I had a look at the "might run" ZXR250A engine I got as part of a recent parts deal. Decided to do a leak down test. Realised something very wrong with this engine and started tearing it down. Found the issue fairly quickly. Can anyone tell me what's wrong with this picture?

 

Well obviously the valve is made from low quality steel, I mean it didn’t even break, just bent
I dread to think what the piston looks like


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Those marks in the head will buff out... and you should be able to put the valve in the vice and straighten it out.. easy fix
A quick lap job (for some reason that sounds a bit naughty) and you will be right as rain...

You have to be impressed at the PO's faith in Japanese Engineering if he thought that one "might run"... or he was just palin full of Bullsh*t..

In all seriousness though.. I would like to see what remains of the piston... plus I would be checking the rod and the crankshaft.. some serious load went through there...

 

Sadly, damaged piston and number 1 exhaust valve are in the bin. But from my deductive reasoning (and what was left in the chamber) I can only assume the engine dropped the exhaust valve which snapped and then number 1 inlet valve copped a whack for its troubles. I think it dropped a valve because number 2 inlet valve wasn't bent or broken.

So, I guess that the head of the broken exhaust valve jammed between the piston and the bent (number 1) inlet valve. The barrels are in good shape. There's a small flat scratch down the side of number 4, but that was from me having to pull them off the pistons. The cams appear undamaged, but I'll have to measure them to confirm. All the shims were in the 160 to 175 range, so engine might have had a few miles on it. A couple of the valves I removed failed the wobble test, so not sure what maintenance had been done to this poor thing. I will measure valve dimensions and post soon. I've never done a valve guide replacement, so I can have a play with this head since it's beyond "that'll buff out".

I'm wondering if these are Chinesium valves? I should have a real ZXR valve laying around somewhere, so I can measure and weigh both to compare. This engine has been apart at some stage as the pistons and the valves are very clean. No carbon build up whatsoever. Engine may have been put back together badly and that might have been the main contributor to the failure. I will have a look at the bottom end, but I'll be surprised if it's damaged. Rods are intact. I will split the cases when I get a chance. Won't spend too much time on this engine as there are plenty of other chores to do.

 

Car stuff! Sorry, a different world. Our little motorcycles have small delicate parts.
The heating of the head and freezing of the guides I agree with.
I have always used a custom made drift and a hammer. I would never use an air tool because I need to feel what is happening. If a guide does not want to budge then it will make the wrong sound and have the wrong feel. Time to stop what you are doing and make a new plan before you break a piece of the head. Motorcycle guides have a flange on the cam side and can only be removed by driving away from the combustion chamber. For fitting guides I always measure the guide and the hole to determine correct interference. In many cases it is necessary to make custom guides. Some bikes like Ducati's have oversizes available. Valve seats almost always have to be recut after guide fitting and cannot be lapped because the valve axis centre has changed.
Often I would ream guides and fit new valves with coated stems rather than fit new guides, being a much cheaper solution.
Cheers