Hello chaps

Question regarding different piston types.

My bike is a 1980 DT175 (G)

I got my hands on two different Wossner forged pistons:

1. The first for a DT175 82-10;

2. The second for a 175MX Thru '77, '79-81 (also listed at CT-2).

The first piston is clearly wrong for my bike as it seems to be a few mm longer and will likely hit the head.

The 2nd, supposedly correct piston (based on what the supplier said), has the correct dimensions however the ports are round rather than square like the piston that came out my DT.

Any ideas if the round port holes on the piston will be a problem?

Thanks!

Aye yak" Wossner are good quality,,,the crowns are usually more domed than OEM. Pistons , if the ports [window] are different, use a dremmel and burr to match Original dimensions ,,

Cheers Blackhat!

Think I'll get away without changing the port window size?

I'm not that handy with a dremmel.

Thanks!

Hi

I have a twin shock DT, the piston on the left is the original 30 odd year old item, the piston on the right is a later type listed as suitable for a MX as well as my bike, I know it has a hole in it that is a different tale, anyhow my bike runs fine with the later type piston, (the hole is because it was originally running a bit too warm) it now runs same type as the one on the right and is jetted slightly richer than standard to prevent more melted piston tops,

Thanks Nayruf!

I have the opposite of your issue, my bike originally ran a piston simialr to the one on the right of your picture (with the big windows), and now I have a piston similar shape to the on the left (my new Wossner) with small windows.

Any ideas if running smaller windows will cause issues?

Cheers!

Hi

All I can say about running differing pistons, is my bike had the small port pistons and the small end needed replacing, I changed to the larger port piston and all seemed to run ok, the bike started pinking at higher revs/speeds and the large port piston got holed, I put this down to advance/retard sticking and higher ethonal fuels making the motor run warmer, I suppose the larger ports in the piston could of been adding to the problems, I am now running another large port piston but I have increased the main jet size and and the bike is now running a little richer, It still shows indicated 68 to 70 MPH flat out but I don't push it any more and I stick to around 55 to 60 max, in all respects the motor starts, runs, stops, hardly ever misses a beat so long as the points and condensor are pretty good,

This is the info on the box from the large port pistion my bike is currently running, its a cheap pistion, I think I got it from 'Yambits' it is listed for DT's from mid 70's to early 80's my bike is a 76,

if you have a piston with large windows , if it was mine i would enlarge the holes or you may find the small end is getting starved of fresh cooling fuel /oil charge. an hour with a few small files will sort the problem.

Remember " the old style pistons, had no windows, did these windows not come in with the introduction of Reeds, /

the purpose of getting the charge of fuel into the crankcase earlier ,,

Never had any issues with small ends on my H2, it was old piston type, I think after market Small ends are suspect,,nowadays,

I always use OEM,

OEM is the way to go. iv had issues over the years with tuned 2 strokers and windows. certain engines all be it race engines i removed the rear of the piston skirts removing the windows completely to keep the small ends oiled.