Have had this DHM piston/head combo for a couple thousand miles now. It dominates the local grom scene. Walking 143s, 186 and neck to neck with a finbroBBH 186. I rip it up to 11K RPM with the DHM head and it just walks the big bores after 9K RPM. It actually has passing power at speeds now too. The old blue hairs in their Grand Marquis don't stand a chance now.
I’m not sure how to feel about this product, as for the company I have no complaints and alway liked using them for all my grom needs. The hi comp piston I purchased seemed very nice however after installing my motor blew up in a few days I can only assume I must have installed it incorrectly. I am not sure if it was my mistake or the product but based on DHM’s reputation I will give them the benefit of the doubt and will continue to use them as I now need to rebuild my motor
Haven't quite put a 100 miles on it yet, but so far pretty happy with it. Acceleration in the higher rpms is definitely noticeable, gained a few mph as well. Only real complaint at the moment is 4th gear seems a little more sluggish now unless you wind out 3rd before hitting it, especially in any kind of wind, but I'm addressing other things (clutch) to hopefully cure that. (If anyone reading this has other ideas to fix that issue or things i should look into, please email me at [****])
If you have basic mechanical skills and knowledge, tools and access to youtube, the install is pretty straight forward. David is also very helpful if ya have questions. I've never worked on a bike in my life, all cars/trucks, and it took me about 5 hours start to finish taking my time.
Keep up the GREAT work fellas
I would love to give 5 stars but I keep having the issue of it falling on its face hard when I take off in first gear other then that it’s awesome!!
DH Motoring Stock Bore Racing Piston (Gen 2)
The DHM Race-spec stock bore piston has produced more HP than any other stock bore kit and is the highest compression stock bore piston on the market. It has a high compression dome that is made exclusively for us and isn't available anywhere else. It's gone through extensive testing on the racetrack and has proven to provide the most power possible from the stock bore.
- ~13.2:1 compression 52.4mm stock bore piston
- Larger ring and skirt oiling holes than other pistons on the market
- Larger oil spring to increase oil volume between the oiling rings
- Oil ports under the pin holes to keep the wrist pin lubricated
- 360 Degree skirt design to increase overall strength
- Racing piston ring kit with pins and circlips
- Valve reliefs that clear valves up to 27.5/23.5 cylinder head valves
- Includes a new base gasket and head gasket
- Requires NGK CR9E (6263) spark plug
- Requires at least 91 octane fuel
Over the past 6 years we've raced with and tested over a dozen different stock bore pistons. Using our experience on the racetrack we've now designed and produced the most competitive and reliable stock bore piston on the market. We targeted increased lubrication while also pushing the compression limits for pump fuel and ended up with what we feel is the most refined 125cc piston available. By enlarging the oiling holes that feed the oil spring channel and skirt, the piston stays well lubricated at all RPM which allows for extended high RPM use. Valve reliefs have been sized to allow the largest valves possible with the stock bore and they have been cut deep enough to ensure compatibility with even the highest lift cams on the market.
**Installing this piston requires setting the ring gaps. If you are not comfortable with this, please have your local shop perform the install. Failure to set the proper piston ring end gap can result in premature failure or seizure of the engine. We recommend an end gap of .007-.009" on the top ring and .009-.011" on the bottom ring. The silver ring goes on top and the black ring below. Unknown Overland does a great job of explaining this in the video below.