Engine Rebuild 4.2

[nzmike]

Hi all, I am about to embark on an engine rebuild on my S1 4.2. Are there any recommended mods or upgrades that I should consider when doing the rebuild? Many thanks.

[abowie]

Not really. It's quite a good engine as it it.

From top to bottom, some comments. Not exhaustive but hopefully helpful.

Do NOT try to remove the 3 hex water jacket head plugs in the valley in the head. If you bugger those threads they are very hard to fix. If you have any doubts about the spark plug threads get them repaired.

Get your tappet bores recut to fit long skirt oversized cam followers. This is by far the best way to keep valve train noise to a minimum.

Avoid the "uprated" braided hose cam oil feed pipes. They actually seem to restrict oil flow and we have had a couple of engines with noisy valve gear due to inadequate oiling which got better when the standard pipes were refitted.

Use quality brand name timing chains and don't get ones with joining links. Make sure you get a quality lower cam chain tensioner; do not use the Rolon branded ones.

We don't have access to a competent cam grinder here so we don't get the cams reground. If you can access a someone who actually is competent it's worth getting the cams at least measured to see if they're in spec.

I went through a phase of using ARP head studs. They're nice to use but quite expensive and I've now gone back to using the standard OEM ones. Don't use ARP conrod bolts; they have a chamfer under the head which may impair their ability to torque up correctly. We routinely reuse the original crank cap bolts without any trouble.

It doesn't really matter which head gasket you use as long as it is of reasonable quality. The Cometic gaskets are nice if you need extra thickness to reduce compression (see more below) but they are expensive and I just use the Payen ones available from the usual suppliers now.

With a 4.2 we usually remove the old liner sleeves and fit new top hat liners. The 4.2 blocks are prone to cracking between the bores, and this solves that problem. It also puts the block back to standard and enables a more thorough cleaning of the block. This adds $1000 or so to the machining cost but is money well spent.

Pay attention to how much skimming of the block and head has been done before ordering pistons. If you fit 9:1 pistons on an engine that has been skimmed a lot you will end up with higher compression than original. If your cylinder pressures are too high (190 plus) you will end up with trouble with pinging. Don't hesitate to use 8:1 pistons to keep your compression around 170 psi. Any brand name piston from the usuals should be fine.

I have fitted "uprated" oil pumps in the past but to be honest the standard units don't seem to give any trouble.

A screw on oil filter adaptor suits some and not others. I have them on 2 of my cars and a standard canister on the third.

It is possible to get a modern lip seal for the rear of the crank. These do have their fans but my read of people's experiences is that they are just as likely to leak as the original rope seal. Personally I wouldn't go for one.

Get all the mechanicals properly balanced. Make sure the sludge plugs in the crank are removed to clean out the oil ways. Fit new plugs.

Don't bother lightening the flywheel. The engine is all about torque and is more than powerful enough to cope with the standard one. Too light a flywheel may make moving off from a standstill harder.

Throw your old clutch away and just completely replace it with a brand name new one from the usuals. Finding out in 12 months that your clutch is stuffed means taking the engine and gearbox out to replace it.

Get the front and rear seals replaced on your gearbox. If your box is perfectly fine leave it, but again now is a good opportunity to sort out bad synchros etc while the box is out.

Tail shaft uni joints. Ditto.

[nzmike]

Many thanks for the detailed response Andrew, much appreciated.

[mgcjag]

Great write up Andrew......Steve

[abowie]

Welcome.

10 years of being the unpaid apprentice has paid some dividends, and I reckon I've built 20 engines (including 4 for myself) by now.

Sadly Chris and Alan are both well over 70 now and the business will be shut down by the end of this year, but it's been a great learning curve for me.

[max-it-out]

Sometimes people talk about " Blueprinting " or polishing the ports on the cylinder head - is it a waste of time/money or a route to better performance ?

[christopher storey]

Polishing the ports is a waste of time and modern thinking suggests it may be detrimental because it reduces turbulence which is necessary for good mixing of the air/fuel . What probably is worth doing is making sure that the carbs to manifold interface is accurately located and that there are no large steps between carbs and manifold and manifold and ports ( both inlet and exhaust ) . What I would emphasise from Andrew's splendid summary is that balancing , both static i.e evening up the weights of pistons , conrods, bearing caps etc , and dynamic - ie of everything that goes up and down and round and round in the bottom end, including flywheel and clutch , will pay enormous dividends in refinement

[Tom W]

Blue printing just means carefully assembling the engine to factory specifications. Where there’s a factory tolerance on something, it means making sure all the parts are as close to identical as possible, and not just within the tolerance band. It also involves building to the end of the tolerance band that will liberate the most power. Sometimes that could be at the expense of longevity. For example, bearing clearances at the larger end of tolerance would give less drag, but the engine is closer to being deemed worn out.

As Christopher says, don’t polish the ports. Cleaning up manufacturing defects doesn’t harm, but doing anything that substantially changes the shape requires experience, and an understanding of what you’re trying to achieve. Given we don’t spend all our time driving at wide open throttle, the part closed throttle plate is the biggest restriction anyway.