408 Stroker Engine Build Up

Last month we talked about whether to rebuild or replace an engine. We also talked about decisions that need to be made. I am currently building a 408 stroker engine for my 1998 Dodge Dakota which is currently equipped with the 318 5.2L engine.

A stroker engine increases the stroke of the engine. This makes a smaller engine deliver more power and torque. Many engines can be stroked including 4 cylinders. Increasing the stroke of an engine is as easy as installing a new crankshaft. The crankshaft as longer throws to increase the stroke.

The first thing I did was searched for a starter engine. I needed a Magnum 360 and all I really needed was the block. Searching on eBay got me the block I needed. I drove down to southern Indiana and picked it up from Indiana Core. The block was in great shape and included pistons, crank, rods, cam, etc. I brought the block home and mounted it on my engine stand. If you are doing this at home, make sure to have a good engine stand. You can get these pretty cheap. I picked mine up at Harbor Freight Tools for about fifty bucks.

After the engine was mounted on the stand, I removed everything off of and out of the block. This can get pretty dirty so make sure you have plenty of towels. Also, if you plan on reusing any of your parts, make sure to mark them so you won’t loose them. I am not going to reuse any of the parts from the old engine so most of it was tossed.

After the engine was disassembled, I loaded it back into the truck and took it to the machine shop. I had the machine shop clean the block. The shop soaked the block in a caustic solution heated to 200 degrees Fahrenheit. This cleans away the rust, dirt, grease, etc. Next, the shop checked the block for cracks using a process called Magnafluxing. This process consists of using a high-powered electromagnet to magnetize the block. Colored iron powder is sprinkled over the block. If there are any cracks, the iron powder is drawn into the cracks to make them visible. Luckily, my block did not have any cracks.

After the block is cleaned and checked for cracks, the main bearing bores where checked for alignment. This is done using a micrometer. My block was just fine. If the main bearing bores are out of alignment, then a process called align-boring or align-honing would be used. Next, the head deck surfaces are checked for flatness. Again, mine was fine, but if not, the head deck surfaces would have to be fixed. This process is called “decking”. Basically it mills the head surface until it is flat.

The next step was to bore the cylinder to .030” over. This process uses a machine with cutting wheels to remove material inside the cylinder walls to fit bigger pistons. This process can also be used to remove piston sleeves on some engines or to prepare for new sleeves. Make sure that when ever you have the engine bored and honed that the machine shop uses torque plates. Torque plates simulate the clamping force of the head and will give you the best finish on your cylinders.

Once the engine was bored, it was time to cut notches in the block. On a stroked engine, notches must be cut in to the block so the rods to not hit the block. When you increase the throws on the crankshaft, the rods will swing out further. This should also be done before the cylinders are honed.

The last step was to hone the cylinders. This process is done honing stones. The hone creates a crosshatch pattern on the cylinder walls. Make sure the shop uses a honing machine and not a drill with a hone attached.

Check back next month as we talk about assembly of the stroker. As always, if you have any questions, please contact me below.

CYA next month!
Vincent Wright
sales@kmwperformance.com
http://www.kmwperformance.com