Classic Harley Davidson Knucklehead Engine

This is a printable working model of the iconic Harley Davidson Knucklehead engine. This is the engine that changed american automotive history.

The original was 61 CI and my model is approximately 60%, so it is around 600cc.

Started with the engine casings and the stands and will upload other parts in due time. In the photos you can see the whole model already has finished, but I need more time to prepare the files and the instructions.

The casings are printed flat on the bed with the mating faces down. You will need supports and I advise 5 or 6 perimeters with at least 50% infil.

I used paint on supports organic style from build plate only. I also advise to use a small ramping lift, because if you do not the nozzle may knock over supports before you are done with them.

This model uses a substantial list of bearings and other fasteners plus hardware. Be prepared to purchase these from Amazon or local hardware stores. A full BOM will be uploaded soon, as well as instructions for printing various difficult parts.

Also, this model is not a simple print and stick together. You will need to make some parts fit and insert a large number of brass threaded inserts. It also uses threaded studs and aluminium tubing, which you have to make to length, so some metal work is also required.

UPDATE 13/03/25

Added the crankshaft components. Full bom list will be added shortly. The lobes are glued together with the lobe studs. After that wait for the bom list because you will need to build it with the bearings and piston rods as one assembly.The bigend pin and the forkrod need supports from the buildplate. Remember to give them a high number or perimeters and infil for strength.

Also added the bearing list spreadsheet. in the zip file you will find ODS or XLS format spreadsheet. All bearings I used were from Amazon and you can use either the rubber sealed or the steel sealed bearings. If they offer open unsealed bearings, check the width is the same as the sealed version or you will have trouble.

Now also added the hardware list. Most you can get from Amazon or your local DIY store. In the zip file are ODS and XLS format spreadsheets

Last but not least added cylinders, heads rocker boxes and the lifter blocks. All these parts print without supports and do not need to be glued.

You can use the head gasket if you want, it is not needed but looks nice if you do it in another colour. This is it for today.

Update 14 March. 

I included a 100 mm calibration cross so that you can more accurately check your e-steps. because some parts will be printed flat on the bed but their interaction in the engine will be with the Z axis direction of other parts. So to make sure you will not print parts that encounter a negative interference, and will not fit, you should calibrate your x, y and z axis to within the same margin of around 0.1 to 0.2 mm on the 100 mm of the cross. Please start with this check to make sure your machine prints with the same error in all 3 directions.

Added all the missing files and made notes for printing on the download file. read the notes carefully before printing. The cylinder halves may need supports depending on how well your machine prints overhangs. The pistons have small flat areas to be a bit forgiving on these areas.

Supports are needed on those parts where indicated so read them before you download them and follow the instructions.

This was a mega project for me that went all the way up to V10, so please forgive me if I muddled up some of the parts or I forgot some. Just pm me or comment and I promise I will read them and reply.

There is the main crankshaft gear and worm, which is a compound part and this will generate a warning from prusaslicer. It will warn you that it is a multiple object in one file and will ask you if you want to import this as one part or multiple part. Your answer should be ONE PART!

This is it unless you find missing parts. I will try to answer fast and add them as I find out about them.

Update 15 march

added some instructions for supports that I forgot.

Also on the camchest lid, use some clippers or needle nose pliers and very carefully remove those supports.

Rotate the parts so they are most logical and with no or minimal supports needed. For instance the cool fins of cylinders and heads are upright, otherwise you will need supports everywhere.

UPDATE 17 march

Uploaded zip file containing spreadsheets with instructions for printing and building and screenshots of some parts on how to print them. also the final bom list of parts to print.

UPDATE AUG 2026,  Redone some of the parts without cut outs on request. NO CUT in the name!