Over the course of two days, Stephen Payne and Aaron Donohoe tackled the task of replacing the cylinder head gasket on the left cylinder head of our latest acquisition - 79 MN 522. Below is an illustrated report of the repair. It should have normally taken a day to remove the cylinder head, replace head gasket, refit cylinder head and manifolds - it took us two days due to stubborn, inaccessible bolts, studs and nuts, as well as encountering difficulties removing the head.

Checklist:

1. Workshop - it wouldn’t be advisable to tackle this in the open, a workshop would be best, for convenience more so then anything!
2. Tools - Good quality, heavy duty tools, inc. a Torque wrench, mallet, multiple ring, adjustable, open, angle and ratchet spanners, sockets, and a rubber mallet are all essential.
3. Lighting - Inspection lights, and background work lighting.
4. Trolley Jacks - Leopards have their engine mounted upside down, on its side, so the cylinder head is located on the right hand side of the bus. Trolley jacks come in handy for bracing the head lightly when removing and for making it 10x easier when refitting.
5. Workbench - You need somewhere flat, clean and secure to put the cylinder head, head bolts, exhaust, air and water manifolds.
6. Assistance - You can’t feasibly do a Leopard head gasket by yourself. It makes sense to have another person to help reduce the work load.
7. Patience - It’s a long job, you’ve to drain the cooling system, remove exhaust, air and water manifolds, remove the air filter and housing, cylinder head cover, rocker shaft, push rods, inlet pipes, injectors, and it’s a task getting the cylinder head itself off!

We backed 79 MN 522 into Workshop one, leaving enough clearance on the offside to get adequate access and workspace on that side. Workshop one is big enough to fit our longest coach 355 SZB (12m) comfortably, and a double decker at a squeeze. Workshop two will be double the size of Workshop one, once complete.

To get access to the cylinder head, to the stage where it’s ready to be removed, you must remove ancillary parts such as Air Manifold, Exhaust Manifold, Water Manifold - with Thermostat, Air Filter, and disconnect all corresponding hoses.

Firstly drain the cooling system, once done remove/disconnect hoses in relation to the parts that have to be removed. Now start by removing the water manifold - this is the first manifold, it comes in two connection parts, one contains the thermostat. Both sections are joined by a copper sealing ring (cause of many water leaks on 0.680 engines). Once removed, store carefully and keep gaskets and bolts safe!

Next remove the exhaust manifold. We encountered a problem, the nuts had melted to the manifold, luckily on the side we didn’t need to remove. We have a replacement part, so to save time we cut the manifold in half from the joining ring - which was also seized into place. Again keep the gaskets, nuts and bolts safe. The air manifold is the one at the rear, it came off without a problem, although it did crack at one of the flanges - since repaired.

Now you can remove the Cylinder head cover. It’s advisable to keep the bolts in situe once removed. As they’re different sizes, it makes it easier on yourself if they’re in the correct order when it comes to reassembly. You can now proceed to remove the fuel delivery pipes, and clamps - cover the outlet pipes, disconnect leak-off pipes and remove the injectors (3). Now remove the Rocker shaft with care, untighten bolts evenly, and lift assembly clear of it’s locating studs. Remove the Push rods, and place in order of removal. Remove cylinder head nuts in reverse order (a manual/diagram comes in handy at this stage), and place in order of removal.

Ensure all Cylinder head bolts are removed, and tap the cylinder head to break the seal. We now encountered a problem, that the cylinder head wouldn’t budge! We tried manually removing it, and bracing it with a jack and trying to pull it clear. We located two unused holes above an below two of the cylinder head locating studs - one either side, and we manufactured two 8mm plates to go over the studs. Two holes were drilled in each place to locate and tighten nuts onto. This method slowly pulled the cylinder head off.

For some reason this method of removing the head wasn’t mentioned in the manual. It was under the advice of Willy Doyle, who had previously worked on such engines, that the recommendation of the two plates came from.

With the cylinder head removed, a well deserved rest was in order. Illustrated is the stripped side, and the complete side with rocker shaft and injectors still in situe.

The cylinder head after removal. Yet to be cleaned and prepared for refitting. Mr KT Lawless, was kind enough to resurface the face of the head for us.

A new Leyland 0.680 Head Gasket.

The old Head Gasket.

Once the Head Gasket had been put into place, and cylinder head cleaned and prepared, it can now be located and fitted. We used a trolley jack to brace it. It slid right on without fault.

Aaron Donohoe locating the cylinder head. Cable ties were used to keep the fuel delivery pipes out of the way whilst fitting the cylinder head.

Now once the cylinder head is located, you can now torque the head bolts, refit the injectors, push rods, rocker shaft, delivery and inlet pipes, cylinder head cover, and manifolds. Once complete, check your work, refill cooling system - check for leaking, check oil levels, and refit air filter. Start the engine (it will take approx. 5-8 minutes to start), and leave to idle for 45-60 minutes. Do futher checks for leakage, and refill water levels.

Job Done!

 

Tags: 0.680, 680, cylinder, gasket, head, ireland, iv, leopard, leyland, motor, preservation, replacement, society, supreme, vehicle