Maintenance Maintenance
Car: Ford | Fiesta | CX (Mk3) | All Derivatives | Hatchback

CVH Cylinder head rebuild

Red Fiesta RS Turbo Restoration

As was the case with the bottom end, the head and valve train had a layer of oil varnish. Again, no signs of sludge. I stripped the head for inspection as most of the valve train components are subject to wear and must be measured. Components are grouped together (right) and must not be mixed.

The camshaft required no measuring, as is usually the case with the CVH the inlet lobe on No4 had worn excessively and could easily be spotted by eye. This wear is due to a design problem with the head, meaning that the lobes on number 4 receive an inadequate oil supply. This coupled with the high spring rates on the CVH means that camshafts wear rapidly.

Red Fiesta RS Turbo Restoration

The cam was replaced but the valve guides and stems were within Ford tolerances so retained, however the exhaust valve seats were very pitted, it is very doubtful if there was even an 80% seal. The photo also shows a sealing compound that had been used on the head, for reliability's sake I sent the head to a local machinists to be re-faced and 'de-coked'.

The exhaust valves had a fairly thick covering of carbon, this and condition of the valve seats points to leaking valve stem oil seals. A build up of carbon on the valve stem can compromise gas flow by a significant amount.

Red Fiesta RS Turbo Restoration

With the head stripped I could remove any carbon from the exhaust valves. I then set to the laborious task of lapping in the valves, this a time to be glad that you have an 8v motor! 2 hours later and I had managed to remove all the carbon and pitting from the valves and valve seats. The photo (above left) shows the results of this work.

I re-assembled the valves and springs with new valve stem oil seals. These are the later 'top hat' type that are sandwiched between the valve spring and the head. Earlier types were independent and simply pushed over the tip of the valve guide, and often 'rode up' with the valve which caused oil leaks.

Red Fiesta RS Turbo Restoration

The valve guides came as part of a 'top end' gasket set from Ford (left photo). This includes all the gaskets required to completely rebuild the head, including throttle body and ISCV gaskets.

As the head bolts are simply standard 10.9 grade bolts, I tend to go for pattern part items, as Ford bolts are 3x the price and offer no improvement in quality.

I always use Ford head gaskets as good quality is assured, however for the FRST the Felpro gasket has also been proven to work well.

Red Fiesta RS Turbo Restoration

After the valve components have been assembled the cam can be fitted. A new cam must always be fitted with new lifters (right), it is complete false economy to mix a combination of worn item and new in this area. If the lifter bores are damaged in any way then the head is scrap, oversize lifters are not made for the engine and sleeving would be prohibitively expensive.

Finally the rocker arms were inspected for wear, all were in very good condition so were refitted.

Completed head:

© Mark Stewart, Wednesday 15th June 2005
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