Forged piston by Competition Distributing
- Forged piston by Competition Distributing
- fits 61 cui Models 1915-1923
- 2nd oversize
- aluminum
- Ø 84.7 mm
- nominal bore: 3-5/16 ”
- compression: 6:1
- with rings, 0.625” wrist pins and snap rings
- USA
- gross weight: 1.33 kg
If you look up old parts manuals, you won't find oversize pistons for the IOE models. Replacing a piston wasn't an easy thing then as Harley-Davidson from 1914 on equipped all pocket-valve engines with conically bored and honed cylinders and cylindric pistons. Of course, oversized pistons were available to dealers, but boring a cylinder was a task that one would maybe like to leave to the factory — and of course the factory offered this service.
The then used piston types nowadays not being readily available nor the friendly factory service being offered any more, our range comprises modern oval shaped high strength and highly heat-resistant pistons that are forged from 2618 aluminum and heat treated to T61. As with all modern pistons the cylinders must be cylindrically bored. The 30° piston dome will give you about 6:1 compression ratio but may be machined to lower compression to 4.5:1 stock compression rate. .003” clearance — as indicated on the piston packaging — is a good starting point for engines that are low compression, subject to moderate loads and that are broken in carefully. Heavily working higher compression engines may nevertheless require up to .008”.
Oil rings for IOE pistons
Actual oil rings supplied with the pistons may differ from those pictured. This does not affect function.
Pistons — Dos and Don'ts
For the pistons that we regularly offer in our online catalog, we indicate the diameters that we have measured ourselves. So not only the nominal bore diameter. For this, we randomly measure the delivered goods.
What can this information tell you? How can you use it?
It can serve as a guide if you are not sure which piston to choose. The diameter + the piston clearance suitable for this piston type gives the diameter that the cylinder must have. The fact that this may not correspond exactly to a specific oversize bore is of secondary importance. Oversizes are nominal sizes and tend to be a rough guide. Whether the calculated dimension from diameter and running clearance fits your cylinders is something you then have to determine and evaluate based on the condition of your cylinders. Or you can have a trustworthy workshop have a look at it.
What does this information not tell you? What should you not do under any circumstances?
The specified diameters are not absolutely guaranteed. Yes, we are responsible for our information. But, when measuring, there are tolerances, also depending on the environment temperature. Therefore, you will not have your cylinders drilled and honed in advance. Doing so will go wrong in most of the case. Do it the old-fashioned way: measure the actual piston yourself after purchase, add the desired running clearance according to the manufacturer's instructions or the Harley manual, and not only tell the workshop this measurement, but also take the actual piston with the actual cylinder to them so that they have the piston as a sample for their work.
Later 1924→ 61” piston with 0.791” piston pins are not available.
Have any questions?
Our service team will be glad to help out: Mondays - Thursdays 08:00-17:00 CET, Fridays 08:00-16:00 CET, Phone: +49 / 931 250 61 16, eMail: service@wwag.com