I keep finding surprises with this engine tear-down! I was cleaning up the head and noticed a large crack between the valves on one cylinder and a thinner crack on the other cylinder. How serious are these? I can't find my valve spring compressor so couldn't get the valves out tonight to see how far the cracks go. I don't know what a 'normal' 500 head should look so, does it look normal otherwise? Sure is a poor looking casting.
Technical How serious are cracks between valves?
- Thread starter marcus550
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Technical How serious are cracks between valves?
Cracks between the valves is usually regarded as a scrap head. It's sometimes possible to remove the valve seats, weld the crack then machine for and fit new valve seats (+ guides) but its not usually cost effective , cheaper to get another head (have you checked the cost of a new cyl. head?) unless its something very rare. The marks in the combustion chamber may have been caused by detonation/pre-ignition, I don't think they are as a result of a poor casting but I could be wrong! Some people leave the cracks alone on the basis that the engine has probably run satisfactorily for many 1000's of miles already and will probably run for many more miles, as it's an air cooled engine there's no risk of a coolant leak into the cylinders. I'd check that the valve seat inserts are still securely held in situ though!
A quick way to remove valves without a spring compressor is support the cyl. head on blocks of wood either side of the combustion chambers i.e. leaving room for the valves to open, place a piece of tubing (an old spark plug socket will do) on top of the spring collar and hit it with a hammer or mallet if you prefer, the collets will pop out of place leaving the valve free to be removed, repeat on the other valves. WEAR EYE PROTECTION.
A quick way to remove valves without a spring compressor is support the cyl. head on blocks of wood either side of the combustion chambers i.e. leaving room for the valves to open, place a piece of tubing (an old spark plug socket will do) on top of the spring collar and hit it with a hammer or mallet if you prefer, the collets will pop out of place leaving the valve free to be removed, repeat on the other valves. WEAR EYE PROTECTION.
This crack was enough for me to replace the head. Quite possibly the engine may have been running lean, overheated, burned the valve and cracked the exhaust port. I didn't ever get the head checked in any detail, but more than likely it may have also been warped. Either way, it went to the bin.
Someone had also dropped a screw/bolt into the engine at some previous time. Probably fell in through the spark plug hole.
Chris
Someone had also dropped a screw/bolt into the engine at some previous time. Probably fell in through the spark plug hole.
Chris
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I can source a new head, but was hoping to find one with a larger intake valve already installed. The VW world has tons of suppliers and dozens of performance heads readily available. I see none for Fiat. Or I need to learn Italian! Also, if I fit 73.5mm pistons/cylinders, do I need a different head anyway?
It depends what you want to do with the car- being Air cooled the cracks between the valve seats are not ideal but usually not terminal.
There are plenty of 500's and 126's running around with these cracks without any real problems- technically the valve seats could drop but it is uncommon. If in doubt it would be worthwhile to get a second opinion from a cylinder head reconditioner.
The pitting on the top of the combustion chamber is usually caused by failure of the top piston ring- they can break up and come through the top of the piston and embed themselves into the cylinder head.
You will possibly need to have the bypass ports welded in the head if you use larger pistons and barrels. The other option you could consider is a 540CC kit of pistons and barrels which will slip into the existing crankcase without machining it.
Alternatively if you are using 594cc Pistons and barrels and you decide to replace the head you could use an early 126 594cc cylinder head to match.
Hope this helps
There are plenty of 500's and 126's running around with these cracks without any real problems- technically the valve seats could drop but it is uncommon. If in doubt it would be worthwhile to get a second opinion from a cylinder head reconditioner.
The pitting on the top of the combustion chamber is usually caused by failure of the top piston ring- they can break up and come through the top of the piston and embed themselves into the cylinder head.
You will possibly need to have the bypass ports welded in the head if you use larger pistons and barrels. The other option you could consider is a 540CC kit of pistons and barrels which will slip into the existing crankcase without machining it.
Alternatively if you are using 594cc Pistons and barrels and you decide to replace the head you could use an early 126 594cc cylinder head to match.
Hope this helps
I have seen some tiny cracks there that have not gone below the valve seats but your one is the worse I have seen by the picture. Another thing to check apart from the condition of valve guides is wether they have dropped. Just worked on two heads recently where this had happened on the exhaust valves.
I have got a spare new old stock unused 500 head here as well as used 594, 652 & Panda 30 heads should anybody be on the hunt
I have got a spare new old stock unused 500 head here as well as used 594, 652 & Panda 30 heads should anybody be on the hunt