DT175 piston

[sydduckett]

A while back i tried a DT175 MX standard piston in my rb20 and it worked a treat, even upped performance a tad. I got a pattern one from jap manufacturer called TKR. i now need to get my barrel re plated and want to send a new barrel with the cylinder. I have found the piston kits for about £40 which is a big saving but there are stating years of manufacture like 78 - 79 & 78 -84. I think they are all the same size (66) so im not sure what diffrences the year of manufacture would make? Anyone have any ideas. i have the box for the last one (TKR) but it doesnt say year or anything like that.

thanks
Sef

[hungdog]

A lot will depend on where the ring pegs are and will probably need repegging to avoid your ports on the cylinder.

[Rich_T]

There are two types that I know of, standard DT175 and DT175K. Both available from Mataka, so I'd find your local dealer with an account and get one through them. The differences are:

DT175, compression height 22.5mm, length 63.5mm, pegs spaced at 25.5 degrees about 12 O'clock position (ie 12.75 degrees each side of 12 O'clock), dome height 3.5mm.

DT175K, compression height 28mm, length 68mm, pegs spaced at 37 degrees (18.5 degrees each side of 12 O'clock), Dome height 5mm.

I guess you will be running a longer rod than normal with a packing plate?

[soullad]

Sef, seeing as how your barrel needs replating, why not buy your piston and then see where the rings fall first, then you'll see if there are any potential issues. You could, if it needs it ,then have any welding etc done to the barrel before sending off to the platers, avoiding any piston repegging. Will possibly save you money in the long run should you need to replace any pistons?
I think it makes good practice to try and get into the habit of offering up all your top end parts if you possibly can, checking things like ring positions / port timings / rod lengths / packer heights / squish etc as you go.

[sydduckett]

There are two types that I know of, standard DT175 and DT175K. Both available from Mataka, so I'd find your local dealer with an account and get one through them. The differences are:

DT175, compression height 22.5mm, length 63.5mm, pegs spaced at 25.5 degrees about 12 O'clock position (ie 12.75 degrees each side of 12 O'clock), dome height 3.5mm.

DT175K, compression height 28mm, length 68mm, pegs spaced at 37 degrees (18.5 degrees each side of 12 O'clock), Dome height 5mm.

I guess you will be running a longer rod than normal with a packing plate?

i have the DT piston in at mo and was able to use with standard set up with no packer, thats why im going for one again. will check for any diffrences in the peg but im presuming it will be the same. When you compare the DT with the one AF sell they are pretty simialr apart from the skirt being a tad longer and the windows being slightly longer.
When I changed from the AF one to the DT the improvment was obvious so i thought i may as well go like for like when i get it replated.

ta/

[john]

Sefs going to be using his car for the next few scooter events

[Rich_T]

What is the compression height on the RB piston? This is the height from the top edge of the gudgeon pin hole to the edge of the piston. You can also check this by pushing the pin half way into each piston and measuring the vertical step between the two piston edges.

If the DT piston has a lower compression height than the RB then you just increased the port timings and reduced the compression ratio.

[sydduckett]

What is the compression height on the RB piston? This is the height from the top edge of the gudgeon pin hole to the edge of the piston. You can also check this by pushing the pin half way into each piston and measuring the vertical step between the two piston edges.

If the DT piston has a lower compression height than the RB then you just increased the port timings and reduced the compression ratio.

im going to pass that question over to john who is my go to man for these sort of questions. Especially as he will be the one helping me...