How to refresh a tired engine on the cheap
If you've seen the build of the grotty Daihatsu Cuore, you'll have seen THIS EPISODE where Marty and MOOG had to get a full rebuild of the three-cylinder EJ-D engine. Years of missed services and general neglect meant the plucky three-pot was needing a full tear-down, new bearings, and a deep-clean.
If you've bought a project with an engine you can see that has missed oil changes, done a million miles, and is ready for a birthday (but you're on a budget), then there is some good news. Building an engine is an expensive process, especially if you're farming it out to a shop, but there are ways to breathe life into an old engine without breaking the bank.
The first port of call is cleaning the engine so you can see what you're working with. Pressure-cleaning the outside and giving it a good scrub with spray-on oven cleaner (remember to wash it off thoroughly, don't let it dry on aluminium!) is just the start of the cleaning process.
Buying a gasket scraper and some wire brushes, plus a couple of cans of both WD40 and a good penetrating spray (to undo tough bolts), a box of heavy duty gloves, a few good plastic tubs, and a 20L can of kerosene will all come in handy.
Put kerosene into each of the tubs, with dirty parts going into one tub and, after they've had 15-30 minutes to soak, give them a good scrub. They can be rinsed in the clean kerosene before having a quick spray of WD40 to protect the raw metal surfaces from rust.
The cleaned parts can then be labelled and put in the clean tub and moved to the side. This saves the labour cost of having your engine builder pull the engine down and sending the parts out to be hot-tanked.
A large part of the expense of an engine build comes down to the hours of labour involved, and paying for precision machining of several key surfaces. The cylinder walls will need to have any wear marks or glazing removed through a process called "honing", which involves a type of precision sanding of the cylinder walls.
While machine shops have automated, finely-calibrated and very expensive machines to do this, for budget builds you can buy a "ball hone" which fits on the end of a drill. Doused in WD40 to lubricate the honing stones, you can then whip up and down the bore to remove any minor imperfections.
Check each cylinder afer 2 passes and if your finger nail gets caught in any scratches or lips, give the bore another pass. However, be careful not to go too far or you'll open the bore up too much to be able to reuse your old pistons, adding dramatically to your build cost.
Wipe the cylinder down with a clean rag when you're done, and give the cylinder a wipe down with fresh engine oil to prevent flash rust forming.
Another area you can save money on machine work is decking the cylinder head mating surface, both on the top of the block and the bottom of the head. Using a large stone normally used for knife-sharpening you can lightly skim across the surface of both decks.
It is vital you run a brand new stone sideways so it reaches across the whole surface in one go, and keep checking to make sure the surfaces are flat. Don't trust your hand - get a known straight edge and lay it along the deck surfaces.
Decades ago it was almost considered routine maintenance to have your engine torn down every 100,000 miles to have new piston rings and bearings added. Over time the piston rings in an engine will wear and running an engine longer between oil services, taking a lot of short trips, and high mileage will all increase the wear on piston rings, which will ultimately lead to blowing smoke and a loss of compression.
Cleaning your stock pistons and con rods, while adding new piston rings, will help make your engine run like a new one for years to come, and saves the expense of buying new pistons.
If your engine has signs of wear on parts like the crankshaft and camshaft you can have them polished back to serviceable condition using linishing paper. This isn't normally a job for novices because you can polish too much and then the crank and cam won't fit back into your motor - you'll need new bearings sized to work with the now-machined parts, too.
This is where it can be handy to have someone experienced in building engines come and give you a hand, so you can measure the parts to work out what size bearings you need.
If any of this is intimidating, a good idea is to buy an old lawnmower, motorcycle or pump engine and practice rebuilding that. They're cheap, simple and will teach you many of the tricks you'll need when working on four-stroke car engines.
And remember, the Internet is probably you're best resource - there aren't any engines out there which haven't been rebuilt at some point, and someone will have put information online about it. If you don't have a workshop manual, keep Google to hand and do a lot of research before you dive in.