dt 250 piston in a ts1 pro's and con's

[tavspeed]

anyone running a dt250 piston in their ts1,are there any issues with ring peg position etc,i am eventually going to have my ts1 barrell re sleeved,so look a good option as plenty of oversizes,what rod are you using and are you using piston bushes,cheers

[Rich_T]

Both DT250 and TS250er pistons are suitable but will require 18mm wrist pins. I use modified TS250er pistons on the GT240 and GT250 kits, it was flatter if I remember). You will need to increase the rod length to 110mm as a minimum at which point you might as well stroke it to 62mm (or even 64 if you want to go mad). Depending on what you are doing with timings and stroke you may or may not need to machine the cylinder base gasket face.

[Warkton Tornado No.1]

Recently rebuilt a blown TS 70 mm that had thrown a rod necessitating extensive 'porting' into the bottom end (effectively to tidy up the slot created)

I bought a Mitaka DT250 non Dykes piston from Grampian to go with the 60 mm stroke long rod crankshaft. The rod was already suitable for 18 mm wrist pins.

I repegged the piston rather than faff about with fingers.

It was a very extensive rebuild IMO but all the more impressive that allied to a 34mm PWK & filter started with half a tentative kick.

It really has turned out to be a really good engine using a scrapped TS barrel.

I use the TS250 pistons a lot in piston port engines & always wondered why the DT250 wasn't the natural choice in reed engines, to the extent I've asked a certain UK manufacturer........(They are only 1 mm different in crown height & already have a port inlet side)

It looks like you have been answered by the earlier response

[tavspeed]

what rod did you use warkton,only rod i can find is the gt rod 110mm with a 18mm small end,as the compression height on the dt piston is 34mm,this would give me 144mm total length,so would i have to machine 2mm off the base of the cylinder to get piston level with gasket face
putting those figures into a timing calculator with a 60 stroke crank i get 186 deg ex duration,with a 60mm crank should only have to take 1mm off the base??

[Warkton Tornado No.1]

what rod did you use warkton,only rod i can find is the gt rod 110mm with a 18mm small end,as the compression height on the dt piston is 34mm,this would give me 144mm total length,so would i have to machine 2mm off the base of the cylinder to get piston level with gasket face
putting those figures into a timing calculator with a 60 stroke crank i get 186 deg ex duration,with a 60mm crank should only have to take 1mm off the base??

I'll check my notes when I can, but more likely that the rod was in the ball park of 115 - 118 centres.

Derinately a thicker base packing than 1.0 mm as I recall.

I tend to go for the longer rods with use of thick base packing as I always match transfer porting using them as templates from barrel to case & vice versa plus any increase in bottom end volume is welcomed IMO. I can't subscribe to the school of thought that deliberately NOT matching transfers is going to gain anything, despite the implication that dyno tests prove otherwise.

The small margins that exist by using 'best practice' methods are worth having on a lower state of tune compared to one of the latest kits that have massive reed intakes & more auxiliary transfer ports than were once common place.

[tavspeed]

rd400 and ktm 200 rod are 115 and 118,but 16mm pin,so would need piston bushes wich i would want to avoid,gran turismo have a 125mm long maico rod advertised with a 18mm pin,so would need a 13mm packer with a 58mm stroke crank,would you have problems with the exhaust or head cowel hitting frame tube

[Rich_T]

With a 13mm packer it will be close but would go if you used eccentric cones for sure.

60 stroke looks reasonable timing on a TS1 if you run a "0" deck height and machine the squish clearance in the head. If you run the piston out the top of the cylinder (-2 deck height) to keep the timings down and go up in stroke but but its risky and perilously on the edge. I have Maico rods in stock with a shorter 22 x 40.5mm pin so it goes straight into a normal crank.

[Warkton Tornado No.1]

rd400 and ktm 200 rod are 115 and 118,but 16mm pin,so would need piston bushes wich i would want to avoid,gran turismo have a 125mm long maico rod advertised with a 18mm pin,so would need a 13mm packer with a 58mm stroke crank,would you have problems with the exhaust or head cowel hitting frame tube

On the TS 70 x 60 mm engine, I anticipated having to use bushes, but did not require them. So I must dig out my notes from within the garage somewhere

However, I recall that the packing was substantially less than 10 mm & obtaining a wider wrist pin bearing easily & cheaply.

I profiled the head on my lathe fixture plate & as previously mentioned, the crown for DT250 is the same as TS250. As it's difficult to turn using a profile cutter without getting chatter, I tend to finish the face by sticking a polo shaped piece of self adhesive abrasive paper to the piston crown & finishing by hand to obtain a consistent squish.

The engines I build have a spigot fit of head to barrel if possible to centralise & seal. Otherwise I've made hollow dowels for two diagonal stud centres. I also do that & the bottom end for the barrel to case/packing. Fussy in the extreme.......

I must confess that the case involved was drastically ported by previous owners & most tuners/dealers would have rejected it or got it welded in the transfer areas. As it is a TV200 block, I persevered & externally, it maintains it's external appearance. It's like a Tardis inside though

On the point of bushes, I have used them for years, from hard steel type to the proprietary plain bearing sort. I've never had an issue, but "keep an eye on them" as Ralph Saxelby used to say.

The flanged type Glacier bushes are in a few engines of mine. The flange itself can be quite useful in taking up slack between piston faces & the conrod faces or for controlling wrist pin bearing float.

As for repegging, similarly, no problems ever. I used old needles from bearings. I know that one very vocal tuner has slated them, but he must have done something different to me for failures to occur. I suppose when somebody so important is so busy reinventing the wheel & claiming so many "first to do this, first to do that's" such little details as engineering fits might get neglected.......