I might not be able to repair this one.

[tony.mon]

Not really. I was aware of what was going on, and it was as I was beginning to pull away from a roundabout, and it made a hell of a noise, and was all over in a few seconds.
I knew it was fatal engine damage straight off, and then slowed fairly gently to the side of the road, without touching the rear brakes as I was expecting oil from the busted cases all over the rear tyre.
So whipping in the clutch, hit the kill switch and front brake gently to a stop.

Daft thing was that the poor old engine was still trying to tick over on just one, with all that wreckage going up and down, in and out..... sounded like an earthquake in a scrapyard..

[ging500]

Well I can say if this was to happen to someone, Mr Mon is the person to take it in his stride. Me personally I would have cried and then cried a bit more. Then would gone and sat in a dark room to calm down.

[Bananaman]

Well I can say if this was to happen to someone, Mr Mon is the person to take it in his stride. Me personally I would have cried and then cried a bit more. Then would gone and sat in a dark room to calm down.

+1

[AMCQ46]

Didn't you all notice that tony has been missing for about 2 weeks since it went pop

I think he didn't want us to see him cry, but he is calm now.....well based on his jokes, he is back to his old self now

[tony.mon]

Didn't you all notice that tony has been missing for about 2 weeks since it went pop

I think he didn't want us to see him cry, but he is calm now.....well based on his jokes, he is back to his old self now

Been busy planning the Engine That is Yet to Come....

And getting money together.
Anyway, it's no disaster, but an Upgrade Opportunity, that's the only way to keep your sanity.

Today the old lump's coming out, and we'll see, maybe the replacement standard one's going in. Depends on if I need a snooze later.....

[Duffy1964]

[quote=

Today the old lump's coming out, and we'll see, maybe the replacement standard one's going in. Depends on if I need a snooze later.....[/quote]


Did you fit my old lump and get her beating again fella?

Impressed with the old one, you blew it good and propper, not seen one go like that before Tony

Good luck anyway

[tony.mon]

Knocked off work early today (well, left at the proper time, anyway) and went straight out to get it finished.
But the battery was flat again (I'll have to check, there appears to be some current drain- alright if used daily, but goes too flat to turn it over in four or five days).
Then discovered that I'd used my exhaust nuts on someone else's bike, so had to order some stainless studs and nuts; hopefully they'll be here for the weekend.

Apart from putting the exhaust, tank and seat on, it's done.

Shame you had fresh oil in it, as I wanted to fit my four-row oil cooler, and can't be bothered to drain and refill, but then on a standard lump the extra cooling isn't really needed....
It'll do for now, while I build something interesting to go in it.

[agentpineapple]

good work tony, you'll be back on two wheels, god help all of us.......

[Duffy1964]

Nearly there then mate, well done, try not to blow this one up

[sirch345]

Might take a bit of polishing:




Well, as I always say, if you're gonna do it at all, do it properly.
Mind you, the front one is still ok....

Well you certainly did it properly Tony.

It looks like it got a little hot, what were you running in on, aviation fuel

Good luck with the new engine,

Chris.

[tony.mon]

Super unleaded with an ignition advancer.
It wasn't melted, just battered. Three valve heads in the combustion chamber apparently don't fit very well.

If you look at the bottom picture you can see where the piston has a small round hole in the middle, this was caused by a section of valve head that had turned upside down; the valve stem stub punched a hole.

I know this as I found the neatly punched slug of piston in the sump,
Underneath the piston are the letters J and E cast into the piston before it's machined (JE Pistons) and at the underneath end of the slug is the letter "E".
Neatly done, engine.

One interesting thing, the undamaged (front) piston also has marks where two of the valves touched the piston head, and also touched the sides of the valve cutouts machined into the piston.
It appears that there wasn't enough clearance.

Ah well, the next one will have oversize valves fitted, and so the cutouts will have to be machined out anyway, and next time I'll add a bit of clearance as a safety margin.

Can't do this until I get cams and pistons, though, and dry-assemble the engine to measure clearances and see what touches where.

So for now it's running a std lump, I'll just have to make do.

[Hairy biker]

Now that's what I call a job well done!

[sirch345]

Ah that explains it now Tony, I bet you were gutted once you'd worked that out. Unlike you though to get the squish clearance wrong. I guess none of us are perfect all the time no matter how hard we try. At least you have a working bike again, so that's good

I hardly think any bike producing around 100bhp is making do

Chris.

[tony.mon]

Ah that explains it now Tony, I bet you were gutted once you'd worked that out. Unlike you though to get the squish clearance wrong. I guess none of us are perfect all the time no matter how hard we try. At least you have a working bike again, so that's good

I hardly think any bike producing around 100bhp is making do

Chris.

Chris, squish clearance is a peripheral band around the outer circumference of the piston face, which effectively squeezes the mixture into the middle of the combustion chamber so that it burns cleaner, and there aren't any unburnt sections of the fuel mixture.

In my case each valve sits in its own cutout in the piston head, and the clearance is the distance measured between the piston head and the valve face. Now interestingly the clearance isn't necessarily at tdc, because the cam isn't timed to have maximum depression of the valves at tdc.
So you have to dry-assemble the engine, using only one of the two valve springs on each valve, then,m timing the engine correctly, revolve the engine a small amount at a time and push the valve down until it touches the piston.

Measure the gaps, and the minimum clearance is a definitive setting, different in exhausts and inlets, which allows for a little extra valve movement- because the valves travel downwards very quickly, then stop and return, but of course even after the cam stops pushing the valve downwards, inertia means that it continues travelling downwards a small amount before the spring pressure stops it and it starts to return.

In the same way the piston doesn't suddenly come to a dead stop on its upward path as it reached tdc, because the con rod stretches slightly and allows the piston to deform upwards ever so slightly.

In this way the clearance allows for these movements and (hopefully) prevents metal to metal contact.

With mine, although the cutouts in the valves are sufficient to allow the valves to sit neatly into the pockets machined into the piston, if the valve timing varies slightly the piston travel moves slightly out of synch with the valve movement and some parts of the pockets have come into slight contact with the valve heads.

Not enough to bend the valves or stop the engine, and probably only actually contacting when the engine is over-revved, on high rev downchanges or a missed gear , for instance, and clearly, in my case, eventually one of the valves cried enough and deflected sufficiently to stress fracture a valve stem near the head which allowed the valve head to drop into the combustion chamber.

Jealous of all the attention and excitement, several other valves joined in.
The piston tried to push them out of the way through the head, and finding itself not quite strong enough, collapsed parts of the piston head to allow bits of incompressible metal into the crankcases.
Other bits of metal flew upwards into the inlet and exhaust tracts, as the valves weren't in place to stop them.

Fun isn't it?


Daft thing is, I probably COULD rebuild this engine and get it running- there's not much bore damage, no visible or measurable damage to the cams or front head/piston, and so with a new head and a pair of standard pistons it would run ok. But tbh the bores were getting quite worn, and it was using some oil, so I won't bother. And I can't confirm whether the crank has twisted slightly, or guarantee that all of the little bits of metal are out of the oilways, so it's best scrapped.

[sirch345]

Tony, very good of you to go into so much detail on this subject, even though I am reasonably familiar with what the squish clearance is about and what happens if you get it wrong. I would say you were really unlucky, as your calculations must have been very close to being spot on, otherwise you would have had bent valves long before the engine went pop. Even though still rather annoying after all the time and effort, plus the expense you put into building that motor. I can quite understand why you wouldn't want to risk using that engine again, especially with those little particles that made it into the lubrication system, I agree it would only take one partially blocked oil way to wreck a new build motor.

Out of interest how does the standard engine feel compared to the modified one when it was going well

Chris.