Jump to content
Sign in to follow this  

How can you tell when It's time for a new top end?

Recommended Posts

My sons 1997 CR80R seems to be sluggish in the mid range before it "gets on the pipe". It runs pretty good for an old bike but cleaning the carb only helped a little. I re packed the silencer a while ago and admit that I may not have done it well. It also seems to smoke a little more than normal.

Any suggestions?

Share this post


Link to post
Share on other sites

Honda service manual says to replace the piston and rings after 15hrs of racing and replace the rings at 7hrs racing.

Id say a 97 has more than a few hrs put on it, so a new top end and it will pull real strong.

Compression test would tell you also.

  • Like 1

Share this post


Link to post
Share on other sites

My 0.02

If you don't want to waste money and want to avoid guess work, then buy a $10 Harbor Freight digital micrometer and a $30 service manual. Take the top end off (gaskets are

cheap). Check the ring end gap first. The bike will run with a ring gap up to 0.25 inch or more, but really, anything over 0.10" is wore out. OEM rings are cheap. Examine and measure the piston, checking for cracks and the condition of the ring slots. Also examine and measure the cylinder and compare to the service manual recommendations. Measure the bore at the top just under the mark the rings make, and be sure to measure it front to back and also side to side to check for roundness--there is an allowed tolerance here. While the top end is off measure the side to side clearance on the rod big end, and feel if there is any up and down play on the rod big end bearing (there should be NO up and down play, and the 80cc bike will not tolerate a sloppy rod bearing for very long).

Then buy OEM rebuild stuff if it needs it. As cheap as gaskets are, there's really no reason to guess at when the top end needs rebuilding. It needs rebuilding when it wears outside the factory tolerances. That might be 15 hours of race time, or it might be several years of riding in the backyard time. Most people honestly have no idea how many hours are on their play bikes.

  • Like 1

Share this post


Link to post
Share on other sites

Good info plynn. If you have access to a compression tester it might be worth a look to see what it is. They cost about 30 bucks at advance auto. If you don't know when the last time the top end was done I would do it irregardless but the tester would give you a baseline to go off of next time. Once the new piston is broken in test it and then once the compression starts to drop rebuild it again. Two stroke top ends are very easy. The only scary part is the unknown abuse from the previous owner to the bottom end. If you plan on keeping the bike an hour meter is worth it's weight in gold. Heck it would probably even help resale value if you show records of everything that was done at each interval plus it will make it easier for you to judge when maintenance needs done. Again they cost about 30 bucks as well. I know the little 30 here and there does start to add up but it will save you money in the long run if your going to keep the bike around for a little while.

Share this post


Link to post
Share on other sites

Hard to start, buy a compression reader for top end, build a compression tool found here on TT, read plug, or motor seizes. I don't prefer the latter.

Share this post


Link to post
Share on other sites

Here is how I know when my bike is ready for a new top end. My bike will start to pop or miss when hard on the throttle. It is really hard to start and doesn't have as much pep as is used to. Sometimes when people say their bike feels slow or doesn't pick up as fast, it can usually be attributed to a worn out clutch. Honda recommends a new ring every 10hrs and a new piston every 15-20. But what I have found is that Honda is assuming that you are racing every weekend and racing hard. I can run on a top end for a year and then in the spring my bikes get new top ends even if they still run great. If you followed Honda's service limits you would go broke, some of their limits are a tad exagerated, but then again its there way of insurance against the customer trying to say they were in the wrong.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...