Vintage Dirt Bike Q & A

Hi,

I have recently begun working on a 1974 Honda Elsinore MR175. It was my father's and has been sitting for at least 15 years. The piston is gone, but everything else should be functional. A rag was stuff into the crankcase as a means to keep dirt and dust out. They cylinder head was removed some time ago, but I still have it. I want to rebuild this bike to the state that it can be ridden again. I have never done anything like this before and am on a relatively small budget. Where do I begin? I know that the top end of the engine will need to be rebuilt, but what about the bottom end? What other areas should I look into? I would like to reuse as many parts as possible. How do I go about cleaning them? Is this even a feasible project or will it end up being too costly? I'm not looking to do a perfect restoration by any means, just enough to make the bike ridable and look presentable.

As you can tell, I am quite new to this and appreciate any help I can get. I have only a shop manual that I found with the bike and a desire to learn.

If you use eBay as a parts source it will average ~$30 for each part that is missing.

The piston would be one of the more expensive items if you can find one. Try to find the correct size piston with rings rather then buy them separately.

It is reasonable to expect to get it running for about $60 but you may have to scramble to do it. This assumes the only thing you need is the piston and make your own gaskets. This would just get you something that you could putt around on or list for sale as running.

Doing it close to right to where it would be safe to ride can be expensive. Just replacing the 30+ year old tires can cost a couple of hundred bucks.

Rick

I agree with ricortes, the piston and rings will be hard to find. Also you may need a wrist pin and bearing. Keep watching ebay or maybe someone out there reading this forum has them.

The most likely areas for work are cylinder rebore, carb cleanout, big end bearing, crank main bearings, crank seals.
If the bike was stored indoors and your father only removed the cylinder you could assume that the main bearings and seals are okay. These could be replaced by a rookie at home but it is a lot of work.
A bad big end bearing will cause you the most work. There should be no up and down play of the rod and the crank should spin freely. Put some 2 stroke oil down there to lube it up and then lift up on the rod and then hit downward on the top of the rod with the palm of your hand. There should be no loud clunk that indicates a gap from bearing wear. A bike shop can help you with this check.
Measure your cylinder bore for wear to determine if you need the rebore and to what size. Then start looking for your piston and rings of that size or larger. A bike shop could help with the measurement. If you're lucky it may only need a honing. Don't bore it out until you get the piston and rings because you might only be able to find bigger ones than you really need.
Pull the carb apart and clean it out carefully. You might need carb cleaner if gummed up badly.
The MR175 is a really fun bike. Good luck with it.
You should use a proper head gasket. I don't think you can make one. Watch ebay.

Thanks for the advice. Is it possible to make one of these bikes road legal? I know that a lot of work would first have to go into making it safe and road-worthy (turn signals, mirrors, etc.), but is it possible to get it registered and insured when it was never intended for road use?

It is possible to make it road-legal...depending on where you live.

In most states and canadian provinces on a bike newer than 1973 it will need an other stator-coil for the battery circuit.It needs a battery for the signal lights and it needs a HighWay legal headlight (the MR 175 headlight is offroad legal only), It also needs a different rear light with brake light, an electrical horn and mirrors, and make sure the tires are DOT legal.

Find out exactly what you must have to make the bike legal for street use before you start otherwise don't bother....the there is the paperwork with the registration.... .
It may have to have a DOT inspection....again, depending on where you live.

If you manage to make it street legal, I can also recommend to change the gearing/sprockets to 39 tooth rear and 15 front to be able ride on the highway.
I own a '77 MR 175 that I made street-legal with help from a donor MT125 bike for the electrical.
Mind you, the VIN plate says "For Off-Road Use Only"


On a final note.... mdlafferty had some wise word regarding the piston.
I chased an oversized piston for over a year, and thanks to member on this forum, whom I am grateful to, hooked me up with an NOS Wiseco piston.
Honda MR175 pistons are obsolete. You may try rings at cmsnl.com Wiseco discontinued the MR 175 piston line in 1985.
If you can find a Wiseco piston NOS, a 0.5 mm(0.020") oversize is a Wiseco number 340-P2.

Mike