I successfully mounted a Grubee Whopper Stopper 4 stroke engine (Stage II kit) to a Felt MP.
I really like the frame geometry on this bike and my other motoredbike, the Felt Iron Bolt. Things to consider when building the MP: 1) Get rid of the rear wheel. The stock internal shifting Nexus hub does not allow for BMX style chain tensioners to be installed. BMX or RMX chain tensioners are mandatory on this bike, as the motor tends to pull the axle forward. This causes the pedal chain to go slack and fall off. Since it has a coaster brake, all of a sudden you have no brakes. Also, if the rear wheel goes out of alignment, the motor chain will rub on the tire and eat it up. Just get a generic 26 inch coaster brake wheel and some BMX or RMX tensioners (such as Diamondback part number 57-18-502 or 57-18-500) you are all set. 2) The newer Grubee Whopper Stopper Stage III (Honda GHX50 Clone) kits have a 3 piece wide crank kit. The wide crankset is necessary so the pedals don't hit the motor. You can adapt the 1 piece bottom bracket on the MP to the 3 piece crankset using an adapter kit. Be sure to ask about this when you order the motor kit. The only trick is to use lots of red Loctite on the threads when you assemble the crankset. Use plenty of grease inside the bearing cups, but don't get any on the threads. I made the mistake of assembling everything with grease the first time. The vibrations shook the crankset parts loose, and I had to clean the grease off and reassemble everything with Loctite. 3) You may have to weld the chainring to the spindle. The chainrings have a goofy setup that requires you to pound a pin into a hole to tighten the chainring to the spindle. I couldn't get the thing to sit tight, so I did a few spot welds to make sure it doesn't come loose. I know it will be a pain if I ever have to take the crankset apart, but I don't want the sprocket to slip on the spindle and lose braking power on a big hill! 4) A front drum brake would be nice for decent stopping power. I am going to see if I can get a front drum wheel from Felt. -Erik
I'm glad someone has at last tried a 4-stroke frame mount on this bike Madbiker1. I've seen 4-strokes on other Felt cruisers but not this one. It seems a shame to swap the rear wheel cos it has 12g spokes and a 50mm wide rim. In Australia the MP came with a front Dynamo coaster brake combined in one hub. It also had a Smano Nexus 7 spd rear hub. Too expensive to throw out. It is possible to fit a chain tensioner on the chain stay and even possible to fit a spring loaded one as per the many shown on this forum. The mudguard has to be cut away but removing it as some have done strikes me as just devaluing the bike cos mudguards (or fenders as you call them) are essential if you want a dry ride. Short sports mudguards a waste of time.
I've looked closely at the MP and you can see that the clearance between seat stay and tyre is difficult but not impossible. 2 strokes have been mounted successfully and they have the same chain. You need a 48T sprocket and special clamping gear for the Nexus 7 spd. I can supply that to anyone who wants cos I make the clamp from 318 marine grade stainless with 2 ply rubber cut to fit and 48T sprocket drilled to fit as well. The good thing about the hub gears is that you can change when stationary.
I think that the tendency for the engine to pull the axle forward on the horizontal dropouts is easily overcome with a bit of skill.
The pedal chains often come off Nexus hubs because of one reason I spent ages trying to figure out - the back sprocket is often assembled the wrong way around because it can fit both ways but only one is the correct way. The exploded drawings of the Hub on the Shimano website do not show clearly if the convex or concave side of the sprocket should face in or out. Only one way works and the wrong way causes the pedal chain to come off which is hard to put on again without undoing the whole wheel assembly. Shimano don't mention this in their manuals.
The MP is an incredible bike and built like a brick dunny (outdoor privy) and will last many decades I reckon. The lack of front suspension is a disadvantage but a softly inflated front tyre will certainly assist on bumps.
Your tensioner brings the top & bottom of the drive chain very close Madbiker.
The other problem with the MP is fitting the tank so it looks good. Rubber belting seems a good material but fixing it to look good is a challenge. Looks are everything to a proud MBc member!
Can you post more pics of this build cos it's a first and well done Madbiker but you do need a front brake .
I'm about to try brazing V-brake bosses to seat stays with Mapp Gas and Sure Fire Torch so stand by for the results. Discs are my preferred brake but a V-brake sure beats a coaster if you need to throw out the anchor quickly.
The MP was $1200 Aus last year but they've stopped importing it and Felt are stopping making it. That's the trouble with Felt - all silly poems and not enough spec data on their website and catalogue. They must think the market is full of pre-pubertal idiots with access to Daddy's wallet. Maybe they are right. Also Madbiker the one piece Grubee crank would look much better on the MP than the 3 piece. Nobody can get them just now because Grubee are pushing that 3 piece with short crank arms but soon the suppliers should come to their senses and order them in. The 3 piece has its purpose if you have a cruiser with a 3 pice BB but that is the only occasion I'd ever want to use one.
The pic is from last week when I was still piecing it together. I'll get more when I get home from work in the morning.
