spacer plate querry

two-stroke-brit · Post by **two-stroke-brit** » Tue Oct 20, 2009 7:01 pm

i have seen lots of info for porting of buffalo jugs but i wondered about using a spacer plate under the jugs and skimming the head the size of the plate to get the compression back towhere i started , i see that the porting is of slightly different dims but both seem to move metal from the cylinder in the same dirrection, and would be a realtively easy fix.
your thoughts are appreciated,
thanks mark

tz375 · Post by **tz375** » Tue Oct 20, 2009 8:36 pm

That's the easy way to get transfer timing right but exhaust duration is still too short.

People have been doing it for years and COMETIC sells spacer plates in a variety of thicknesses.

rngdng · Post by **rngdng** » Wed Oct 21, 2009 4:22 pm

I used 74 jugs, with a 2.25mm plate, and additional base gasket on mine. We milled the top of the cylinder 3mm, and installed the stock head. With 34mm VM carbs, K&N filters, and JEMCO pipes, I got 80 HP on the rear wheel.

Lane

CJF · Post by **CJF** » Wed Oct 21, 2009 5:16 pm

Anyone taken a similar approach with t500 engines?

Buffalo-guy · Post by **Buffalo-guy** » Wed Oct 21, 2009 5:45 pm

Lane.
When you did the lift plate conversion, did you leave the porting alone, or did you drop the exhaust and intake ports to match? What jetting did you use on those 34's to get them to work. My hotrod needs to go to the next level. I have a lift plate, and the 34's. Any info would be greatly appreciated.
Thanks. Fred

two-stroke-brit · Post by **two-stroke-brit** » Wed Oct 21, 2009 6:30 pm

hey lane ,what was the reason for using the74 jugs was it available to you or for the upgrade from that year ,talking of that have you seen the juds and pistons etc on ebay #290361557988 i thought worth it just for the wiesco pistons alone. or is the UKNOWN "PROFFESIONAL " a warning.
mark.

rngdng · Post by **rngdng** » Thu Oct 22, 2009 12:54 am

OOPS! I'm sorry guys, I used 75 jugs. With the lift, I'm close to TR specs. The best I can remember, I have 30 pilots, 3.5 slides (3.0 would probably be better) and about 200 mains. I can't remember what needle jets or needles are in there....whatever they had when I got them (came off an H2).

I matched the exhaust ports to the piston tops at the bottom of the stroke and cleaned up the transfers and intakes, and milled 2.5mm off the rear piston skirts, which left the intake timing almost the same (it was a guess that worked!)

Lane

tz375 · Post by **tz375** » Thu Oct 22, 2009 2:35 pm

The reason that spacer plates became popular was with racers who found that when they tried to raise the exhaust to TR specs, they broke through into the water jacket.

Exhaust height measured down from the top are:
J/K/L: 42.5mm
M/A/B: 40.0mm
TR750: 32.0/30.5mm depending on which article you read!

The roof can be raised to around 35.5 or 36.0 on a good casting (doesn't matter what year), but that's still way short of the TR, but add in a 4mm spacer plus extra gasket and it's getting close. It would also be hard to ride on the street.

Transfers are interesting:
Early J: 51.5mm
J-B: 53.0mm
TR750: 49.0mm

Using a spacer and no other porting increases all the duration times but leaves the same blowdown which is a nice simple way to push the overall powerband upwards.

The only way to know for sure whether more or less blowdown would be beneficial would be to try different timings and see the effect, but for a street motor you want to avoid increasing that too much.

So the simple fix is a spacer plate and just clean up the floors of the ports and maybe lower the intake floor just enough to clean it up. too much intake duration will hurt bottom end torque badly.

Lane has sensibly reduced his intake duration slightly.

For a race motor it's a different story and big HP requires wide ports ad they lead to other problems so choose wisely.

Lane's formula clearly works well.

BTW, try not to follow too many old school articles. For example 3mm off the head is said to be safe - It is not.

rngdng · Post by **rngdng** » Thu Oct 22, 2009 5:39 pm

Truthfully, my engine was a guess. I looked at what others had done (including the factory) and sorta picked what I thought would work for me. I got lucky. If I could lower the weight, I would really have something....maybe this winter.

Lane

two-stroke-brit · Post by **two-stroke-brit** » Thu Oct 22, 2009 6:06 pm

many thanks to all.
loads to digest and look at over the winter.
methinks i will get a spare set of jugs to experiment on when i come to it.
cheers mark.

Post by **Suzsmokeyallan** » Sun Oct 25, 2009 9:11 am

Richard if you post up all the Buffalo and TR barrel specs for all the years in one message it can be made into a sticky.

tz375 · Post by **tz375** » Mon Oct 26, 2009 10:18 am

Mark,

When you work out what you want to do, you could do worse that to contact Eric (Zookie) board owner around here or Bill Trippe in Illinois, both oh whom are good with a porting tool.

I use Bill Trippe because he's close and we use different software to work out what we want and then asymptote towards an optimal solution.

Scott Clough of SCR is another racer who makes his living tuning 2 strokes. I only know of one that he did and it was OK. Lanes makes more power with the same pipes!!!! OK so Lane has bigger carbs, and maybe he just got lucky, but then again, I like lucky people.

You could port the barrels yourself, but I try not to because they are too easy to screw up

two-stroke-brit · Post by **two-stroke-brit** » Mon Oct 26, 2009 5:12 pm

thanks i will probably ask zooke when i am ready to go ahead.
i am thinkin i want to have one standard bike and one to make into a cafe racer styley but i am getting ahead of myself.
thanks again.mark

tz375 · Post by **tz375** » Mon Oct 26, 2009 8:32 pm

remember that posting frequent pics is a requirement..

water cooled · Post by **water cooled** » Tue Oct 27, 2009 5:12 am

If the target height for the exhaust roof is 32 - 32.5mm from the deck, is there a dimension that needs to be held between the exhaust and intake roof. (I understand that the intake needs to be lowered to about 110mm but I am concerned about the height of the intake roof).