1971 Honda Scrambler 175

Hello all! I'm new here and this will be my first post.

I just picked this up yesterday for my wife. Runs only on the right side cylinder. Left cylinder has little to no compression going by the "thumb test". It sat for a while. I was hoping the other cylinder would light up after running a bit but sadly it is not to be. I believe I'll be tearing the engine down on it. I've been poking around on this site, found some good info and decided to register and post my findings. I'm only taking the engine out today as I don't have a book. Tomorrow I'll get down to the dealer and see if they have a manual for me. Any suggestions there? I imagine it's going to be a Haynes or Clymer. Also today I figured on putting my left side piston on BDC with the valves closed and putting some compressed air to it through the spark plug hole. I figure that will tell me where it's leaking. Previous owner made no mention of lacking compression. He does have a CB175 that's been wrecked but supposedly a newly rebuilt engine but I don't know if I trust him. I did verify that the valves are working through the adjustment covers but that doesn't mean they're sealing. Still, it feels like there's a hole in the piston. Wish I had one of those bore scopes... Could be that the bike lost compression from sitting, could be the guy is dumb as a rock and never noticed a dead cylinder, could be he knowingly sold me a bum engine. I'll get to it though. There are other issues as well but for now I want to find where my compression has gone.

Hope this pic works.

One thing that's been bugging me besides the compression, when I installed my new battery and had it running, it started blowing light bulbs left and right. finally the main fuse went and the engine died. I checked under the seat and my pos terminal came off. Effectively it was running with no battery. Did this make the regulator go full tilt and burn my light bulbs out? I hooked my battery up properly and it still cranks and runs, really hoping I didn't burn something up...

with out the battery the regulator wont work properly so you lost some bulbs

Check the valve clearance, if it's real loose you might have a bent valve. These engines didn't have rev limiters, and with an aggressive downshift, are known to bend.

It's possible that your bike was built with the "Compression delete" option . Seriously though, do what you were suggesting and add air pressure to the motor but be careful. The compressed air with force the piston down pretty fast, so find a way to Apply a long breaker bar to the alternator bolt to stop it rotating. Then listen for air comng out of the inlet or exhaust port or both. If it comes out of the crankcase, there's a hole in teh piston, but a rusty vave seat is more likely after sitting for a while.

Fortunately, those engnes are light and easy to work on.

Factory service manual and others are available as a download if you search.

Found a manual in PDF and downloaded it. Getting the top end off the engine was pretty standard stuff. Then I got to the spark advancer. I read that they can be a real pain to get loose. Went through the usual bag of tricks and the end of my camshaft came off with it...Not my day I suppose. The cylinder bores look pretty worn and there's some significant galling on the left hand piston. I found a cam shaft on e-bay but at this point I'm not sure the rest of the engine is worth it. Fortunately the previous owner has a wrecked CB175. It got hit in the rear. I talked him down to $200 for the whole thing. As for where it was losing compression, I'm still mystified. Nothing was blowing out the oil fill hole and while blowing air in it I could get both the intake and exhaust to seal up. Perhaps the head gasket but I didn't see any obvious bad spots on it. I'm going to get a shower then maybe sit in the corner and cry for awhile...

S.O.P. my friend. Clears the mind as well as the sinuses.

At this pint I would not worry about what was wrong. Just rebuild it properly and you will be good to go for years. Soak that advancer end of the cam in PB for a few days and it should come off quite easily.

Pistons and gaskets used to be readily available at eeh ebay "parts depot".

Runs great!

My Wife and I did an engine swap. Might have taken three hours or so. The left cylinder was hesitant at first but after some running it came right up. I still want to get the original engine running so I can truly call this bike a survivor.

I can't see how to embed a video, so here's a link. I'm hoping someone can tell me why the tach is spazzing out but I'll research that. I don't want to go off topic.

https://www.youtube.com/watch?v=d75AV35CGuY&feature=youtu.be

Most likely oil getting past the tacho drive oil seal, wicking up the cable and into the tacho head.

That lazy left side is most likely a blockage in the pilot jet or associated passages.

If the original motor had been sitting for a while, the rings may have stuck.