Bongo Fury

Mattylad wrote:HHMM My reply seems to have disappeared on here.

I know it seems very coincidental widdowsman but we are indeed seperate people.

Are there any tests worth while doing to see if the cam shaft snapping is just a cause of something else not being right?

I travel to a festival near brighton next week and am very paranoid.

Matty

Sticking my neck out here, and I'm no expert on this (just applying knowledge of mechanical enginering experience gleened over 50 years.)

I have thought about how the camshaft and bearing housings were possibly manufactured.
Because the cam rotates at a fairly high speed, it is paramount that the bearings are all in line and the only way this can be achieved is to fit the caps and bore straight through in one setting. This means that each cap is unique to its pedestal and are strictly speaking NOT interchangeable. Similarly, to maintain true lineability, a particular cap should be fitted the same way round as it originally was. Any deviance from this will mean that the original alignment is not maintained. The result of interchanging caps will be a slight misalignment which, when the caps are tightened down, will result in one or more of the bearings being tight. At the speeds and temperature we are looking at, the results could be exactly what you have experienced.

So what I am saying is that if I ever had to do this job, I would mark the caps and pedestals BEFORE taking it to bits, and I would make sure that each cap was replaced on its original pedestal in the original orientation.

sorry guys its my fault that the mm bit dissapeared, i selectivley quoted chris's reply,then added a comment,pressed send and the whole lot vanished. .

the point i was going to make about m monkeys woes was that number 1 bearing/pedestal is as far as i know the furthest/highest point from the oil pump,so would be the last part to receive supply, especially if the system has a fault between the pump and bearing mentioned,this could be pump restricted,or previous bearing worn allowing pressure to drop etc.

sorry to mangle the thread .

i seem to recall the cam caps are numbered/stamped.

From all the information I've got now i'm pretty sure I know why the engine failed.
Sometime in the past before i purchased it(only had the bongo 6 months) this head has overheated & distorted the head. It was skimmed up then refitted back. When the camshaft snapped in half at the middle bearing(Its numbered up as no2 but its actually the third bearing from pulley wheel)the engine was suffering the first stages of overheating due to the coolant issue's I was experiencing at the time, even the temp gauge had not had time increase but the the engine bay fan had just come on.
At the engineers workshop it was found top of the head was not parallel the bottom, infact the head gasket face is perfectly flat where'as the top face & bearing seats where bulging up by 0.5mm in the middle right where cam snapped. That's a massive distortion & bearing misalignment so the cam would have been running with no bearing clearances!

Thats my take on it anyway.

thats very interesting,so are you saying that the gasket and head are/were fine,apart from the fact that the cam pedestals are out of line.
the motor must have been running on the edge(probably generating to much heat) until the hose went and lifted the head a tad more thus trapping the cam.
i wonder if some sort of extra temp monitor would have picked this up.

What condition was the cambelt.
If the camshaft is pinched by the out of alignment bearing carriers, the cambelt would have to work harder to drag the shaft around. Did the belt fail/slip and cause valve/piston collision and then the camshaft snapped.

Yeah funny you should mention that because I've got service doc's stating cam belt was changed About 15k miles ago but the belt looked well worn & not far off failing so it must of been working hard. All valve's & pistons are intact.

Northern Bongolow wrote:thats very interesting,so are you saying that the gasket and head are/were fine,apart from the fact that the cam pedestals are out of line.
the motor must have been running on the edge(probably generating to much heat) until the hose went and lifted the head a tad more thus trapping the cam.
i wonder if some sort of extra temp monitor would have picked this up.

Yeah that pretty much it!

have you kept the old head,if so can i borrow it for a look see (i promise not to weigh it in).
just in the interest of science .
how are you doing on the replacement.

Northern Bongolow wrote:have you kept the old head,if so can i borrow it for a look see (i promise not to weigh it in).
just in the interest of science .
how are you doing on the replacement.

Yeah no problem.

got to wait till monday to order from club shop cause of scottish bongo bash.

Those bloody jocks are always causing problems.