Whether you have a problem with your engine or just want to refresh the one in your Spec E30, having a tight, reliable power plant is essential for a fun-filled and cost-effective racing season.

The engine in my Spec E30 was an unknown entity when I bought the car last October. It came with no history other than what I was told by its previous owner. The engine in this car never really felt bad, but it never really felt great either. At its last event, power seemed to decrease with each passing lap. At the end of the race, I heard knocking, which signaled to me that a rebuild would be needed sooner rather than later for this engine.

Who can rebuild an engine? We’ll most anyone with hearty mechanical skills and a decent set of tools can do the job himself. There are some specialty tools you would need for the job. Some are affordable, but others cost many thousands of dollars to purchase. This is why there are machine shops, and some of them can be expensive.

Why so expensive? Much like divorce, because it’s worth it. Machine shops already have spent the big money on all the tools to properly rework the engine and its related mechanical items. You really won’t know what work will be necessary to bring the parts back into serviceable condition until the short block has been disassembled, cleaned and inspected. This could be a simple visual inspection, which you can do yourself, or closer inspections involving more specific tools and equipment. Obviously, more detailed inspections find issues that will show up eventually than an inspection done just by the naked eye. For me, the cost was worth it since my goal was to build a power plant that lasts for many race seasons.

One special tool you will want to purchase, if you haven’t done so already, is a factory repair manual. Within these pages is valuable knowledge you need to inspect and rebuild an engine properly. This is where I sourced all of my specs for rebuilding the bottom end, from torque values to ring gap settings. Everything you will need to know is found within the pages, so there is no guesswork and no Google search blunders.

A machine shop can tell you which items you will need to replace and which items you will be able to reuse. In my case, the machine shop found that my crankshaft had micro cracks forming. This might be considered bad news, but discovering it now saved me from having a catastrophic failure soon after the rebuild. When I inspected the crankshaft, it looked perfectly fine to me. I requested to have the block’s main journals align-bored. I also had the oil galleys cleaned since oil starvation to the No. 6 connecting rod was the cause of the spun rod bearing. The block also required a light machining of the head surface due to some pre-existing corrosion. I now needed to source a crankshaft.

The old crankshaft had micro cracks in it, so I sourced a fresh crank and connecting rods from NASA SoCal Spec E30 sponsor Midnight Oil Motors.
The old crankshaft had micro cracks in it, so I sourced a fresh crank and connecting rods from NASA SoCal Spec E30 sponsor Midnight Oil Motors.
A spun rod bearing on the No. 6 journal was the impetus for this bottom-end rebuild.
A spun rod bearing on the No. 6 journal was the impetus for this bottom-end rebuild.

Luckily, SoCal Spec E30 series sponsor Midnight Oil Motors had a freshly machined crankshaft sitting on the shelf and I was able to continue with my rebuild. They also had a fresh set of connecting rods ready to go, so I opted to go that route. My cylinders only needed honing and I was able to reuse my stock pistons after a thorough cleaning, but with a new set of piston rings, also sourced from Midnight Oil.

While the block was at the machine shop, this was a chance for me to find top and bottom gasket kits, rod bolts and a head bolt kit. My oil pump checked out OK, and I could have reused it, but I opted for a new oil pump and a new oil pressure relief valve. Since the oiling system circulates the life blood of the engine, having new components served this build the best. The existing parts are likely the original parts that were originally assembled with this engine back in the 80s.

Once the block and parts are all collected, you can begin the assembly process, which for me, began with a coat of fresh white engine paint for the block. You will want to paint the block to protect it from rusting after its been cleaned. Plus who doesn’t like a clean engine bay? Why white you ask? I like white for the engine block because it shows any oil or fluid leaks that might spring up. It just helps to see in the engine bay, too.

While the block was drying, I sized the rings to the cylinders one at a time until each ring was precisely gapped. This is a process in which you must take your time, because you cannot “unfile” the rings once you have removed the material. The work determines the pace. This required some light filing and installing the ring in the cylinder bore to measure the gap, removing a small amount at a time until you achieve the perfect clearance. Repeat for each ring for each cylinder. It takes a few attempts until the gap is exactly what you want. Again, take your time! Once done, I assembled the pistons and rod bearings onto the connecting rods. The next step was to install the rings onto their pistons and set them aside. Prior to cleaning the pistons, I marked each with its cylinder number so I could get them all back in the right bores.

Take your time while filing the rings to get the proper ring gap. Push the ring into the bore with the head of the piston and measure the gap with a feeler gauge.
Take your time while filing the rings to get the proper ring gap. Push the ring into the bore with the head of the piston and measure the gap with a feeler gauge.

The keystone to any bottom-end build is installing the crankshaft. The machine shop told me what size main and rod bearings I would need. Don’t just take their word for it. Verify their measurements and use Plastigauge to measure the bearing clearances for all the main and rod bearings. Once the main bearings are installed in the block, set the crankshaft in dry and use Plastigauge to check the clearances for each bearing. If everything checks out, remove the caps and carefully and completely remove all the Plastigauge, leaving none behind. Then you can use assembly lube on the bearings and torque the main caps down as outlined in the repair manual.

To check the clearances between the main and rod bearings lay a strip of Plastigauge across the dry journal, then torque the main and rod caps to factory spec.
To check the clearances between the main and rod bearings lay a strip of Plastigauge across the dry journal, then torque the main and rod caps to factory spec.
After you disassemble the main and rod caps, compare the compressed Plastigauge to the dimensions printed on the package. If they match the specs in the factory service manual, you’re in business. If not, you might need different thickness bearings or machine work.
After you disassemble the main and rod caps, compare the compressed Plastigauge to the dimensions printed on the package. If they match the specs in the factory service manual, you’re in business. If not, you might need different thickness bearings or machine work.

Next, install the new front and rear main seals. I previously installed my seals into their housings after I cleaned them up and set them aside for this very moment. Use a little bit of engine oil on the seals so they slide over the crankshaft easily as you work the housings onto the dowels, and tighten them down.

The M20 engine uses full-floating wrist pins, so you can press them into the rod with hand tools.
The M20 engine uses full-floating wrist pins, so you can press them into the rod with hand tools.
Once the wrist pin is centered on the rod, install the snap rings in the piston.
Once the wrist pin is centered on the rod, install the snap rings in the piston.
If the clearances for the rotating assembly are within tolerances, coat the bearings with assembly lube and torque the main and rod caps to factory specifications.
If the clearances for the rotating assembly are within tolerances, coat the bearings with assembly lube and torque the main and rod caps to factory specifications.

Now flip the block over and drop in each piston. I apply a light film of engine oil on the cylinders and pistons. Use a piston ring compressor and carefully tap each piston into its cylinder. If there is resistance, don’t force it because you will break a piston ring. Pull it out and start over. Also be sure to align each piston so that the arrow points to the front of the block. Failure to do so will cause damage to the valves and likely the piston.

Align each piston so that the arrow points to the front of the block. Failure to do so will cause damage to the valves and likely the piston.
Align each piston so that the arrow points to the front of the block. Failure to do so will cause damage to the valves and likely the piston.

Once the piston pushes past the ring compressor, make sure the rod is guided onto the crankshaft. You already should have installed the new rod bearings onto the rods and rod caps as well as purchased new rod bolts. Install the rod cap and new bolts finger tight for now until they are all in. Then you can repeat the Plastigauge dance with each rod to verify the bearing clearance is correct. When done with all six rod bearings, remove the rod caps and completely clean the Plastigauge from the crankshaft and bearing surfaces. Then use assembly lube on the bearings and tighten to the final torque.

Make sure the crankshaft rotates freely 360 degrees. Now you can now install the intermediate shaft and gear with its new seals. I also opted for the Ireland Engineering oil pan baffle and windage tray. To install the windage tray, you will want to temporarily bolt it to the block with a few bolts. Turn the crankshaft by hand to see if there is any interference between the crankshaft and the windage tray. I had to lightly massage the windage tray for the crankshaft to clear.

Once the windage tray is ready to install, you can now install the oil pump and pressure-relief valve. Remember to install the oil pump shaft that connects the intermediate shaft to the oil pump or you will never have oil pressure on start up and you will have quickly ruined the engine within minutes of startup. Turn the intermediate shaft by hand and verify the oil pump turns freely. I also previously installed the oil pan baffle by bolting it directly into the oil pan sump area. It takes a little bit of puzzle work to get the oil pan on the block with the baffle installed, but it does fit.

The sump baffle and windage tray from Ireland Engineering help control oil slosh and parasitic drag from oil on the rotating assembly. Be sure there is no interference between the windage tray and the crankshaft when you assemble them.
The sump baffle and windage tray from Ireland Engineering help control oil slosh and parasitic drag from oil on the rotating assembly. Be sure there is no interference between the windage tray and the crankshaft when you assemble them.
Even if your oil pump checks out OK, like mine did, it’s cheap insurance to replace it. Remember to install the shaft that drives the oil pump.
Even if your oil pump checks out OK, like mine did, it’s cheap insurance to replace it. Remember to install the shaft that drives the oil pump.
It takes a little bit of puzzle work to get the oil pan on the block with the baffle installed, but it does fit. White engine paint shows any leaks and helps visibility when working in a dark engine bay.
It takes a little bit of puzzle work to get the oil pan on the block with the baffle installed, but it does fit. White engine paint shows any leaks and helps visibility when working in a dark engine bay.

The rest of the accessories get bolted back onto the block the same way you removed them. Replacing the unknown entities like the oil pressure switch was an easy decision since its an affordable item to replace. My water pump and timing belt tensioner had been replaced a few months prior, so I reused them. These are important components and should be replaced at the time of a rebuild.

A new oil pressure sensor also is cheap insurance against leaks and malfunctions.
A new oil pressure sensor also is cheap insurance against leaks and malfunctions.
Be sure to install the head gasket right side up. It will fit on upside down, but it will block oil and coolant passages.
Be sure to install the head gasket right side up. It will fit on upside down, but it will block oil and coolant passages.
With the long block assembled, you can begin to install the peripheral equipment. It’s a good idea to replace the water pump and timing belt tensioner.
With the long block assembled, you can begin to install the peripheral equipment. It’s a good idea to replace the water pump and timing belt tensioner.

Now put it back in the car and go racing!

Ready to go back in.
Ready to go back in.

 

RESOURCES

Midnight Oil Motors

Ireland Engineering

http://www.bmw2002.com

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Image courtesy of Shawn Meze