Engine Rebuild

How to make sure all your components fit together perfectly

B-series pre-assembly checks.

n this instalment of our B-series rebuild, we’re dealing with one of the most important steps in engine rebuilding: final checks and measurements. This is essential to avoid wallet-withering disappointment. Last time, we took our sad-looking engine parts to Owslebury Crankshaft Services (01962 855969, ocservice.co.uk) who machined them back to tolerance when mated with undersize bearing shells and oversize pistons. Now is the time to make absolutely certain that all the components will play nicely with each other.

We’re not questioning the quality of the components or the machine shop’s work. Tolerances are simply a necessary evil in car manufacture. You’ll see in your manual that every key dimension has an acceptable range rather than an absolute figure. It’s not inconceivable for two tolerances to be at extremes that could result in a tight bearing – or one that haemorrhages oil pressure. It’s better to identify such problems at this stage rather than later on in reassembly.

There’s one process in this feature that’s slightly out-of-step: removal of the core plugs and oil gallery plugs. It would’ve been better to do this before machining, so the exposed galleries could’ve benefitted from the machine shop’s hot parts washer.

The engine has two main oil galleries, each with a ½in brass plug at either end. The block may have an additional ½in plug at one end and a larger one at the other. Remove the ½in plugs to clean the galleries. Replacements are readily available. If you also remove the larger plug, you’ll have to replace it with a screw-in hex plug of appropriate size after tapping the hole.