Welcome to Netrider ... Connecting Riders!

Interested in talking motorbikes with a terrific community of riders?
Signup (it's quick and free) to join the discussions and access the full suite of tools and information that Netrider has to offer.

Need a hone or just rings?

Discussion in 'Maintenance and Servicing' started by sylvaner, Jul 28, 2013.

  1. Hi there guys.
    I have an 1989 DT175 which I purchased for a reasonable price from ebay.
    The guy mentioned the bike has low compression but I chose to purchase anyway.
    As soon as I got it home I stripped the carbies and gave them a complete clean out and I discovered that a green cloth was being used as the air filter (thus justifying the clean out XD)
    anyway.. I measured the comprettion and it came in at a whopping 65PSI.. pretty sure its meant to be around 110-120 but I'm not 100% sure please correct me if i am wrong.

    The bike was running at this point, not idling very low and it lacked power

    I pulled the top end off and took out the piston. The piston said "50" on it which might be stock.

    I only have an imperial caliper so the following measurements are for yall 'mericans
    The gap for the piston measured in at 2.6170 inches and the piston 2.6000.

    My main question for this post is: Am I able to get away with putting in 2 new rings on the old piston and putting everything back together or must I get it machined or honed up to a new spec with a new piston? I want to achieve a higher compression.

    any help is much appreciated and I am very interested in any other information on this bike =D

    Thanks guys.
  2. You really need a manual to be sure of measurements, but unless there is a mark in the cylinder wall you will probably get away with honing and rings only

    This is an intermediate step compared to machining and rings alone. You should really do this if you are replacing rings anyway.

    You can buy honing heads that you fit on an electric drill and do it yourself.
  3. Seeing as you've gone to the trouble of pulling the thing down, get it rebored, new piston and rings.
  4. Get the specs from a manual. If the bores are within spec,a hone and rings will be sufficient. Otherwise bore it to the next size piston.
  5. I hope your measuring all the way down the bore using micrometers.
    Bores "belly" half way through the stroke perpendicular to the crank.
    Measurements can read fine at the top and at the bottom of the stroke but that's not where the wear is.
    You can take the rings off the piston and check the piston to bore clearance using extra long feeler gauges all the way down the bore. (You may even feel the slop half way down).

    When doing compression testing oil resting on the rings increases compression sometimes giving a false result.
  6. Hi guys. I went to Yamaha directly today, I thought I would just ask the pros if they could help out. These guys were actually more then helpful. I thought they would be rude and not want to help because I was doing everything myself but they recommended what I should do in my situation and that is as follows:

    He said that the piston I had was oversized by .50...
    he told me to buy a new piston at 67MM or 1.00
    he said they would charge $269 for piston and rings and I thought that was a joke so I found this on fleebay http://www.ebay.com.au/itm/Wiseco-P..._Parts_Accessories&hash=item4d0f3a2543&_uhb=1
    I did my research on the company that makes the piston and it all seems good.
    Yamaha said that I could try and find something on the internet for cheaper and they could rebore it to suit.

    My only question would be: Do the DT175's all use the same piston? this piston is specified for 79-81 and I am hoping this fits.

    Any clues?

    Thanks guys.