Club 80-90 Forums

Hello all. I'm John and i have been working on the engine of a camper that my friend bought last week...he has requested an engine HERE.
I pulled the engine apart today to find this...



2 questions...what has caused this and has anyone got a pair of heads we could buy?
It looks almost like something has been dropped into the cylinder head..someone mentioned that it could be due to over heating but why is it that the only areas affected are the raised areas?

GSF seel heads my van had 2 new ones fitted

I would replace pistons as well.Looking at the cylinder head it appears to have a crack between the valves .

I would say either overheating (probably due to a lean mixture) or damage caused by a piece of broken piston ring making its way into the combustion chamber.
I have seen this sort of damage caused by a broken piston ring but I would think it's unlikely to happen like this on these engines due to the orientation of the cylinders, ie. horizontal.
The small crack between the valves is common on these engines and can usually be ignored without any noticeable 'side-effects'. (Well spotted though CAPRICE, I had to look twice to see it!)
To be honest, the heads may be ok but I would replace the pistons. Heads are thicker... In my case anyway! Pistons are not and I would think these wouldn't last too long if reused.
I have no idea why the raised areas only have gone like this. Maybe a localising of heat in those areas caused the pistons to overheat and flake off.
Only other possibility is that the pistons are for some reason meeting with the head.
Very strange though!

I am more used to diesels but could it be due to the wrong grade of fuel being used? Someone with more knowledge of that wierd fuel petrol and octane ratings might know.Weren't these engines designed for high octane fuel?
It does look as though something has been bouncing around in there but as it is both pistons so is unlikely.

I think that the combustion chamber shape is what is known as a squish chamber. I believe the idea is that the charge is "squished together in a more compact volume when ignition is initiated so enhansing flame propogation. Therefor a small piece of debris such as a bit of piston ring would simply get trapped repeatedly in the areas where the squish chamber isnt so to speak. What baffles me though is the strange battered look is present in both barrels. If it is indeed battering I would want to look a bit deeper than the heads. Please do tell when you find out.
Cheers
Wolfie

Piston bounce due to very sh****d bigends and small ends?

Oldiebut goodie wrote:Piston bounce ?

An idea to check for overheating is to look on the underside of the top of the piston. If it is darkened or black then this points to burnt oil in this area and would be an indication of overheating.
Overheating can also be caused due to ignition timing being too far advanced. The engine would also be quite difficult to start due to the combustion cycle trying to push the piston against it's natural cycle and effectively trying to turn the engine backwards.

Almost as good as 'pissed 'n' broke'!

I would say either overheating (probably due to a lean mixture) or damage caused by a piece of broken piston ring making its way into the combustion chamber.

Yes, if you can find eveidence of a part of a ring missing (on either cylinder), if not then it can't be..

So, it could be the earth electrode having broken off a plug (due detonation/overheating)

IF that's not possible in a previous or current wonership (plugs not changed due to no sparks)

BUT

The fact it is almost identical on both cylinders, says almost certainly this is due to high-speed detonation (not light tinkling/pinking)

Detonation can erode/melt a piston in seconds ina high performance engine.. in a cooking air-cooled VW it will take longer
Bit this should have been easily noticeable, hot weather, heavy load, lots of throttle and too much hard work....

Is the fan working properly and fully cowled?
Ign timing grossly over-advanced at high rpm (cent or vac advance up de swanny and static reset incorrectly!) - Wiki has a fair bit on air-cooled timing crurves and dizzies, more than a fair bit actually
Did you not hear heavy detonation and a reluctance to pull well at speed under load?

AND

aren't the other two cylinders the same?

Oldie-but-Goodie

Wouldn't you notice no oil pressure and horrendous knocking if there was enough big-end slack to produce that sort of result

HarryMann wrote:[
Wouldn't you notice no oil pressure and horrendous knocking if there was enough big-end slack to produce that sort of result

I would I hope,but they have just bought the van and most probably don't know it's history at all.

Thanks all..as said this van was bought with a known engine problem..that's why it was cheap .
I think the idea of a lean mix is correct as i found BOTH carb mixture screws laying in the bottom of the tin-ware..one looked like it had been there some time!..


one carb has also been leaking and someone has attempted to repair it by covering it in mastic.
I'm pulling the second head off this morning...piston and barrel set is on it's way and i think i have found some new heads.

Sounds like the main cause

The oil ways and crankcase will need a good cleaning out I should think, check the colour of the oil and see if it is full of minute ally particles

I pulled the other side off and it is perfect..no cracks as far as i can see...i have left it soaking overnight so that i can have a better look in the morning.
Pistons should be here Moday and the head on Tuesday..that gives me plenty of time to clean everything down and clean the crank case out...I run a magnet through the oil and it came out clean...still doesn't mean there are no alloy bits in there though.