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Messages - James P

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I think the header diameter on the 370/400 will be too large to fit the 250 manifold.

Yes, you're right of course. I'd forgotten that the RM370 used a different exhaust stub manifold on the cylinder.


PM sent guys

Thanks - replied.

yes they fit I have A RM250B and a PE250B,C the only difference is the baffle in the chamber of the PE and spring location for the muffler

Excellent - thanks for confirming what I thought I knew :) . Should it follow that pipes for all 77-79 PE250, 76-78.5 RM250 and 76-78 RM370/400 are physically interchangeable...?
If they fit, I'd be interested to hear from anyone who has tried an RM370 or 400 pipe on a PE250 (or even vice-versa for interest) - is there much/any obvious difference in the shape, length or volume (internal space, not loudness ;D )? Any observations on performance?

Thanks & regards,

Suzuki / Re: 1978-onwards RM/PE250 lower fork yokes
« on: March 20, 2018, 05:08:09 PM »
...heating is required or you risk bending. Ditto when replacing. for thought indeed. I was tentatively intending to use some heat anyway - I will now make sure that I do. Thanks for the benefit of your experience Momus! 8)


Out of interest, how much do you want for the PE pipe?



Doh! I was going to ask that - you beat me to it Brent! :-[

S27 - Thanks very much for the info...and can I please have second dibs on your now-almost-NOS PE250C pipe?? :D


Suzuki / Re: 1978-onwards RM/PE250 lower fork yokes
« on: March 19, 2018, 05:21:50 PM »
Yes they are just a press fit. They can be removed. Don't loose the fine wire c-clip on the bottom of the stem. You will see it after you press it out.

Excellent - thanks for the info Leith. I knew I could rely on you :) .

I presume there should be no problem reassembling the parts again...? Hopefully everything will be apparent once I get the steering column out.


Suzuki / 1978-onwards RM/PE250 lower fork yokes
« on: March 17, 2018, 09:21:19 PM »
From 1978, lower fork yokes for RM and PE250s were supplied with integral steering columns. Is it possible to press the steering column out of the yoke and later reinstall it without damaging anything?

I can't tell by inspection whether the (supposedly) 1978 lower yoke I've got has the steering column pressed in or cast in...I don't want to scrap the assembly by trying to do the impossible!

Thanks & regards,

Suzuki / Anyone want two 1969 TS250s...?
« on: January 17, 2018, 06:24:49 PM »
I came across these (well, one of them) during a visit to a wrecker recently. I'm not sure how rare they are, but it was the first time I had actually seen one in the flesh (or metal at least ;D ). A quick check of Ebay revealed quite a few NOS parts available from USA. One bike is missing a flywheel rotor, but I must have seen at least five of these on offer on Ebay!

The wrecker (Mark Collins of The Motorcycle Wreckers, North Richmond, NSW) has two bikes; one at the shop and one at home. Each one is missing a few smaller parts. I was tempted, but decided that I already have too many projects and not enough space. I have no financial interest in these bikes, but am happy to recommend Mark as a helpful guy with reasonable prices and a fair amount of stock from 70s and 80s off-road bikes. Asking price for the TS250s is $1000 for both ($500 each).

I took a few photos of the bike he had at the shop and he sent me a couple more of the one he has at home. I'd be happy to pass these on to anyone interested by e-mail, or you can contact Mark directly. This is a link to the Suzuki section of his website, where you can see one photo of each bike:


Kawasaki / Re: KLX250 fork yoke dimensions...?
« on: December 27, 2017, 11:08:14 PM »
Thanks to all who replied, but I have now managed to obtain a set of the correct Suzuki yokes.


Yamaha / Re: Dimensions of yokes for Yamahas with 36mm forks...?
« on: December 27, 2017, 11:06:59 PM »
Thanks for your input everyone - I have managed to obtain the correct Suzuki yokes.


Vinduro / Re: 1980 Suzuki PE175
« on: December 27, 2017, 11:04:03 PM »
Gday guys...
Late reply I know... Currently building a pe175x and I'm wondering is there any mods that need performing on the ts piston or is it a straight up fit for the pe..??

Glen, I have an idea that the piston dome profile is different between the PE and TS pistons. I think the TS piston dome has a smaller radius, so has more of a pronounced dome than the PE piston (the PE piston dome looks flatter). However, this may only be the case for the early (1978-79) PE175 piston with offset transfer cutaways - I haven't got a later one for comparison.
Even if true, it is usually the case that production squish bands are cast to be a little steeper than the piston dome, in which case the TS piston dome could be a perfect match for the PE squish band... :-\ .

However, there is still the possibility that you would have to machine the squish band on the PE head for a) the bigger bore and b) the correct profile. The taller dome and larger bore may also give you a greater geometric compression ratio than you need or want. Squish clearance would also need to be checked.
It may be worth investigating whether a TS185 head (from any of the various versions) will fit the PE cylinder, but (if so) it also may not give the compression ratio or squish clearance you want. Whatever the case, I'm pretty sure the ring pegs on the latest TS185ER piston are in the same positions as those on the early PE175 piston (not sure about later type).

Please let us know if you discover anything more!


Wanted / Re: RM125, 250 or 400 fork yoke set...
« on: December 23, 2017, 01:48:02 PM »
Now sorted - thanks to all those who responded.


Suzuki / Compatibility of early RM and PE expansion chambers - 250cc models
« on: December 23, 2017, 01:30:23 PM »
Can anyone advise whether an RM250A, B and/or C model expansion chamber can be fitted to a PE250B, C or N model without modification to mounting points?

I am fairly certain that silencer mounting points are different, but always thought that the three mounting points for the main chamber portion (i.e. cylinder stub manifold, right-hand front frame lug and left-hand rear frame lug) were in the same relative positions for all these early RM and PE models.

Since I lack enough parts to try out the theory for myself, I am hoping someone has already investigated and can advise accordingly 8) .

Thanks & regards,

Tech Talk / Re: Measurements for side-bleed expansion chamber?
« on: December 23, 2017, 01:21:28 PM »
Think of it this way:
You have a pipe that works well. It has a 600mm stinger.
1. You cut the stinger off where it joins the chamber, make the resulting hole big enough, poke 300mm of the stinger into the pipe. Weld it in place. You now have a conventional pipe with 300mm stinger visible, But should perform pretty much the same? Probably quieter?
2.  You cut the stinger of where it joins the chamber, block the resulting hole. Cut the appropriate size hole in the chamber, weld the stinger into the pipe. Bend the stinger to fit as best it can. (Obviously in reality you’d do all the bending first.) should perform as above, and stock?

I’m far from an expert, but think the engine would “feel” the same thing with all three variations.
Yes, I agree wholeheartedly with your observations and suggestions 8) - the only problem is the location of the silencer. As it would be very difficult to locate it at the end of the "new" stinger for either of your two options, it would be much less hassle to leave it where it is and just increase the length of the stinger to meet it. Naturally, this raises the question of whether to increase the diameter of the stinger to compensate for its increased length.

No one knows the answers James. Make your chamber with a flange, gland or spigot at the end of the baffle cone and test variations. If you do this thoroughly you will probably be the world expert on this sort of empirical testing on your model engine.
Good advice, but I'm trying to get it right first time without having to experiment ;D . Two-stroke exhausts is one area where I prefer to use known concepts rather than to do my own development - I'd much rather buy someone else's pipe (if the design and characteristics suit my needs) than develop my own. I can appreciate how much work is involved in two-stroke exhaust development - I just haven't got enough time or resources to do it.

James P - as to stingers - they are just as complicated as the pipe proper - a good "starting point" is:

What Gordon Jennings said in his paper about expansion chambers.  You can go by his suggestion of making the stinger diameter 60% of the header diameter, and making its length 12 times the distance of the stinger diameter, which works fine for a well designed pipe. Using that as a guide I figured a 125 reving to 10,000RPM needs a 22mm stinger which provides .08psi back pressure. Jennings and Bell both said that the stinger creates pipe back pressure. I'm inclined to have a stinger that gives somewhere between .1 and .5psi back pressure.

Thanks for that info. I had a look at the details provided and further investigated the concept of pressure drop between one end of a tube and the other. Unfortunately, I found the "calculator" on the Gates web-site unworkable - it kept giving figures of zero for all the quantities it was supposed to calculate and annoyingly didn't display the formula it was using.
Nevertheless, I found another formula which seemed to work. I used what I believe to be at least semi-realistic figures for dynamic viscosity and flow rate, but these quantities were constant for every calculation I made - only the length and diameter varied. I made three calculations to suit my hypotheses and obtained the following results:

1. For my existing stinger (25.4mm ID, 380mm long), I obtained a pressure difference (between one end of the stinger and the other) of 0.34PSI.
2. Simply increasing the length of the stinger to 630mm using the same size tube gave a pressure difference of 0.56PSI.
3. Increasing the diameter of the entire 630mm stinger to 28.6mm gave a pressure difference of 0.35PSI.

These results suggest that the pressure difference would increase markedly (65%) if I just made the existing stinger longer. However, the pressure difference would not increase nearly so much (only 3%) if I made the entire stinger from larger ID tube.

My knowledge and experience of fluid dynamics are weak to say the least, so feel free to pick holes in my "logic" ;D . At this stage however, it appears that I can make a new longer stinger from larger ID tube to meet the silencer in its existing position without a drastic increase in heat retention. It is early days yet though, as I have plenty of other things to do along the way!


EDIT: I'm not sure that the quantities I used for calculating the pressure difference were all correct, so you may take the actual pressure results (PSI) above with a pinch of salt. However, the percentage differences obtained between the results for the various stinger diameters and lengths (65% and 3%) work out to be the same, so that particular comparison still seems to be valid.
While I'm in calculating mode ::) I have determined the ideal ID for a stinger 630mm long (to obtain the same pressure difference as I already have with the 25.4mm ID, 380mm long stinger) - the result is 28.8mm ID, not too far from the proposed 28.6mm ID stinger I intend to provide. Perhaps more usefully, I have also calculated the ideal length for a 28.6mm ID stinger - the result is a stinger 611mm long. Since I do have a little room for shortening, I may be able to achieve this figure.
I have to go head is hurting again :-[ .

Tech Talk / Re: Measurements for side-bleed expansion chamber?
« on: December 21, 2017, 11:14:53 AM »
I cant see that there could be much (any?) difference between a “side bleed” and an “internal stinger” that starts where the side bleed would exit. (You could even bend the stinger so the entry was near the edge of the chamber, where the entry to the side bleed would be) Externally, the second option looks standard, just an apparently short stinger (some hidden in the chamber)
Yes, there shouldn't be much difference, but I suppose it depends on whether one wants the silencer to stay in the same place. If so, the "internal stinger" arrangement provides an extra length of tube which is nearly straight (and hence as short as possible), while for the "side bleed" arrangement, the extra length of tube cannot be anywhere near straight (so must be longer)...although I wonder whether this admittedly small difference in extra length would have any detrimental effect :-\ .

I should point out so far that I am satisfied that both "internal stinger" and "side bleed" designs should provide significant noise reduction with little or no effect on performance. The only question which remains is the necessity (or not) of increasing the diameter of the stinger to compensate for the increased length (in order that the cylinder does not retain any significant extra heat).

A suggestion has been made to me for converting an existing "normal" pipe design (with 25.4mm ID stinger, about 380mm long) to the "internal stinger" arrangement, whereby the internal portion of the stinger would be made from 28.6mm ID tube (about 250mm long), but the external portion would still be 25.4mm ID and retain its usual length. As I lack expertise in this area, I must ask the following questions:
a) Would the proposed increase in length require an increase in stinger diameter to prevent excessive heat retention in the cylinder?
b) If so, will the suggested stepped design achieve that objective?
c) If an increase in stinger diameter is required, is it better to make the stinger of uniform ID throughout, rather than the suggested stepped design?

AG Bell offers some handy advice about stinger lengths and IDs in his book (120-280mm long and 26-28mm ID for a 250cc cylinder), but these measurements must only apply to "normal" stinger arrangements because he makes no mention at all of any alternative stinger design. A brief look through one of my other two-stroke tuning books (JC Dixon) revealed some info on both "internal stinger" and "side bleed" arrangements, but annoyingly no advice is given about length or diameter (other than to effectively state that diameter is very important and length is not so important).
Jennings' recommendation for stingers states diameter to be 58-62% of lead-in (header?) pipe diameter and length to be twelve times whatever the stinger diameter is. In my case, the ID of the stub manifold at the cylinder is 44mm, giving a stinger diameter of 25.5-27.3mm and a (nominal) length range of 300-330mm. Of course, Jennings' experiments with internal stingers were carried out while keeping the stinger length constant - only its position was varied.

This comment over on the Penton board may give some leads...

"...Ollie McKagen built some wild pipes. He also designed and fabbed some wild and crazy suspension concepts. He was the smartest/most "out there" guy I ever met...I saw him weld pipes with the "internal stinger". He was extra diligent to ensure the backflow went into the center of the pipe to provide bottom end grunt. He wrote some articles for Dirt Bike or Dirt Rider. He patented several items too. There is some info on him on the Eurospares website...
Thanks for the reference. I have had a look at the Eurospares web-site, but it only deals with Ollie's suspension arrangements (all the bikes in the photos are four-strokes). A few brief Google searches did not reveal any results relating to his internal-stinger pipes, but there were a few more results relating to his suspension arrangements - most particularly his "funny front ends".

Unfortunately I ran out of expertise on this topic a long time ago :( . Also I have to go and lie head hurts :-[ . Further contributions from anyone knowledgeable, experienced and/or interested are welcome!

Thanks & regards,

Tech Talk / Re: Measurements for side-bleed expansion chamber?
« on: December 18, 2017, 12:25:07 AM »
i dont know if you have access to the adb magazines in which you can see the terry schultz job. his stinger exited the right angle bend of the chamber underneath where it turned over the motor (kdx 200) and then the stinger / tailpipe ran just under the chamber before popping up and straightening to arrive at the muffler at the right spot. i think he had a piece of perforated steel as a guard over the lot.

cant place in my mind the PE pipe (i had an x from new) but i think it would be possible. ( note schultz's dx had no side covers or very small ones from memory)
I remember Terry's name coming up in internet searches I did some years ago when researching my previous side bleed pipe. I never saw any pictures of his bike, but I think I can visualise the arrangement from your description. My dilemma with such an arrangement is whether to make the stinger diameter larger to compensate for the considerable extra length...
If anyone can direct me to any pictures of Terry's bike or knows any measurements from it, I'd be glad to learn the details.

What about making a double walled alloy muffler?
The pipe was very loud when fitted with the matching silencer (with either of the two different cores), so I wrapped as much of the pipe as I physically could along with the silencer too, but it didn't make very much difference. Fitting the FMF silencer (not wrapped, but much larger than the original) did make a noticeable difference, but it wasn't quite enough. A double-walled silencer may reduce noise further, but I imagine it would have to be made bigger again - the FMF silencer is already about as big as I want to go.

Today I spent a couple of hours trying to envisage how the existing FMF silencer could be fitted to the bike in a side bleed arrangement. The only real possibility I came up with was to use the right-hand top rear shock absorber mount as a silencer mounting point, by the use of a custom-made adaptor. The resulting side bleed stinger would be about 150-200mm long, meaning that an increase in diameter should not be necessary - I think this is my best bet so far. The silencer would be a little close to my right leg, but I daresay I could fabricate a small tidy heat shield and perhaps wrap the stinger. I would have to drill/bore a fairly large hole (about 30-40mm diameter) in the right-hand side cover to allow the new silencer mount to pass through, so I may purchase a pair of reproduction side covers for this purpose, unless anyone can supply a rough restorable side cover for me to modify :-\ .
I ruled out fitting the silencer on the left-hand side, as it would prevent (or at least seriously hinder) access to the fuel tap and spark plug. However, I'm still open to suggestions if anyone can offer any other solutions.


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