Rebuilding 1980 CR80R

Hello all,

I just joined up to seek some advice on my current motorcycle project. Let me give a little background before getting to the questions so you will know where I'm going with this.

Recently I bought a Sachs MadAss 50cc with a bad engine. Some of you may be familiar with these. It's sort of a mini-motorcycle powered by a version of the CRF50 motor, similiar to a pitbike but designed by Sachs and much higher quality than your typical Chinese toy. The obvious thing to do would be buy one of the Lifan-type bigbore motors that are available in 140-160cc for well under a thousand dollars. But where's the challenge in that?

Instead I am swapping in a two-stroke dirt bike engine. For one I have always wanted a two stroker. I've been into street bikes and have never had anything to do with a two stroke, but they just look like fun. So I went to a local motorcycle junk yard and scouted around for something that I could make fit. I was hoping for something in the 125 to 200cc range, but the most promising lead was a 1980 Honda CR80R. They had a complete bike which simplified things, it is aircooled which was a must for the sake of simplicity, and it's a Honda which may simplify things by keeping it in the family. I've pulled the engines out of both machines and here's what they look like next to each other (sorry I can't post pictures directly):

http://www.flickr.com/photos/22974775@N05/5747434307/

Obviously I will be modifying the engine brackets but it looks doo-able. This should be an interesting bike once it's all done with. The 140cc engines people frequently put in these only make about 15 hp or so and the CR80R is supposed to make 16.5 hp...with two more gears. With the 50cc engine the thing only weighed 212 pounds dry and the CR80 engine is about 9 pounds lighter even including the expansion chamber.

So anyway, the CR80 engine was reported to have no compression. I have the top end off and the piston skirt has come apart. The cylinder is scored and there must be debris in the crankcase. I was hoping to avoid getting into the bottom end but it looks like I will have to. What concerns me most is the lower connecting rod bearing. There is quite a bit of slop in it. Apparently the crankshaft would normally be replaced in this situation? Parts availability doesn't seem to be very good with this old engine. I could probably find one but this is supposed to be a cheap project. Looking at the parts diagram on BikeBandit it appears the crank pin is a separate piece and only $15. Why can't you replace only the crank pin and bearing? I plan on replacing all of the seals and such. Are the main bearings typically replaced in a case like this or only if they are clearly bad?

What about the crankshaft drive gear? I have the clutch cover off and there is what I would consider excessive slop between the crank gear and clutch basket gear. There is visible wear marks on the crankshaft drive gear.

I know my way around engines and have had motorcycle engines apart before but have never split a case. I've been researching this and have been surprised by the amount of special tools that seem to be required. Flywheel puller, crank puller, crank pusher, etc. Maybe I can borrow some of this if I can find a dirt bike guy, and there seem to be some tricks to getting around using the special tools, but this seems to be a lot more involved than I had first thought.

I've got many more issues and more will probably develop as I get further into it but this is probably enough for today. Thanks for any help!

Forgive me for bumping my own post but apparently as my first one it was delayed pending moderator approval which pushed it down to the second page. I know a CR80 isn't as exciting as a 500 but hopefully someone still has something to say about it.

Thanks,

Harry

212 lbs. is heavy for a little bike. Thats getting near the weight of a 250 2 stroke.

I hate to do this to you since you wanted to build this on the cheap but IMO, since you have a 31 year old engine, you are going to have to go through it completely in order to make it reliable. Unfortunately, I don't know where you would find parts for this engine. I think there is a vintage forum on thumpertalk, you might see if anyone there has info on where you can get parts for that motor.

You are wasting lots of time and money. I would build a ZHO155 to a 192 and V2 head.

If you want the easiest 2t that will fit in it then find a good used pw80 motor and build it.

I have a 2001 YZ 80 engine that is ready to go but will need mounts and a radiator.

$250 shipped

Thanks for the replies.

to NSF3537

It may be heavy for a dirt bike but it's very light for a street bike. The frame is steel, the swing arm is steel, there isn't much aluminum on it outside the engine and wheels. The muffler probably weighs 10 pounds alone. Plenty of places to shave pounds down the road.

to frdbtr

You are certainly right, after thinking about it not replacing the main bearings would be penny wise and pound foolish. And actually the online parts houses seem to have most everything covered. I was surprised to find the ThumperTalk parts store section even has a stator/sprocket cover for the engine for only $30. They also have a crankshaft assembly....for $430. Not economically viable for an engine that I only paid $50 for. I'll probably wind up sending a couple or three hundred on parts to get it running tip-top but that's still less than I'd spend on an all new engine.

to Blackwoodz

You could argue that doing anything with motorcycles or dirt bikes is a waste of money, why not just buy a Toyota Corolla and be done with it? We do these things because it's fun, or a challenge, or just because we want to. Anyway I did look into the PW80 engine but it appears they don't have a real transmission. There is a complete running, late model PW80 for sale on craigslist locally for cheap, but my research seems to indicate they all have a three speed semi-automatic gearbox. That won't do. The YZ engine doesn't do it for me either, I don't want to deal with a radiator.

Any comments regarding replacing the crank pin versus the entire crank shaft?

Thanks,

Harry

Edited by SailorHarry
typo

where do you plan to put the carb with that downtube in the way?

to Blackwoodz

You could argue that doing anything with motorcycles or dirt bikes is a waste of money, why not just buy a Toyota Corolla and be done with it? We do these things because it's fun, or a challenge, or just because we want to. Anyway I did look into the PW80 engine but it appears they don't have a real transmission. There is a complete running, late model PW80 for sale on craigslist locally for cheap, but my research seems to indicate they all have a three speed semi-automatic gearbox. That won't do. The YZ engine doesn't do it for me either, I don't want to deal with a radiator.

I understand but somethings are just not worth the outcome. I know this from my past experiences with moneypitbikes. That motor is going to cost way more than the gains it will bring compared to even a stock HO155. As for the water cooled engines....it is well worth it for engine longevity and a single radiator would be very simple to mount....but

hey good luck with your venture into the money pit venture...lol....just don't say we did not warn you.

where do you plan to put the carb with that downtube in the way?

I hope to find an intake boot that will fit the reed and angle the carb off to one side. It needs a new one anyway and looking at pictures certain CR125's appear to angle the carb and have a similar reed. Failing that I may flip the intake over (as shown in the picture) and extend it forward with some suitable thin wall tubing and mount the carb forward and above the engine.

I understand but somethings are just not worth the outcome. I know this from my past experiences with moneypitbikes. That motor is going to cost way more than the gains it will bring compared to even a stock HO155. As for the water cooled engines....it is well worth it for engine longevity and a single radiator would be very simple to mount....but

hey good luck with your venture into the money pit venture...lol....just don't say we did not warn you.

Well you are rather a spoil-sport, aren't you. I don't quite approve of lumping it in with the pitbikes because it's street legal and thus has practical utility virtually lacking in a pitbike. Anyway as I said I don't want a water-cooled engine because of personal preference and the believe that it just doesn't suit the character of the motorcycle at all.

Thanks for the opinions although I shall now seek actual advice over in the Vintage forum.

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