unit53

good point ,i know the crank is different and theres probably better support for the bearings, and hopefully any suggestions jody may have shared got included ,in this new about to be realeased version,i was thinking the same thing as proof my early issue straight plug mt70cc twin ,really runs great,his shop and qc people can be part of a real winning respected team or possibly face other options, just think ,,a real fair priced builders kit?that one can honestly say at least 98 out of 100 will only have simple or no problems,,i would consider that excellent,the way shippers sling boxes,allwats is an issue but yes i really want to see this mtengine line suceed , and as stated,,you cannot repeat the mistakes of the past and expect different results..

unit53

PlaneKrazee

My Feedback: (14)

So,

How's this engine coming along?

Super08

My Feedback: (2)

I think everything is still shut down for Chinese New Year...

unit53

check your mail again

PlaneKrazee

My Feedback: (14)

A two stroke case needs to be stuffed as full as possible for proper pumping action. Can't use a four stroke type crank in a two stroke engine design. If you cut the counter balances off you need to replace them with plastic and the center interconnect needs to be round and full.

aussiesteve

That is not the entire story. Whilst the pumping action is critical, it is also possible to have the crankcase volume to cylinder displacement ratio out of whack and lose power. There is a point where the crankcase volume can be too restrictive and performance will suffer.

The filled crank voids are more to do with turbulence issues than to do with just filing crankcase volumes.

PlaneKrazee

My Feedback: (14)

Aussiesteve,

Are you saying the twin throw crank in the photo would have no excess volume? Please.

If the secondary compression is too high you could loose power but I doubt that will happen in a properly designed engine.

aussiesteve

It is impossible to answer on the volume accurately without seeing the crankcase it is installed into. What that crank wil give is a very turbulent crankcase and a tendency to supply one cylinder wiht more fluid than the other cylinder (I am making an assumption that it is from a horizontally opposed twin cylinder 2 stroke). It is a good example of where performance gains could be made by filling the voids on the crankshaft as shown in your first photo. However, the overall crankcase volume needs to be correct also.

You are completely right, a Properly Desinged engine doesn't have excessive secondary compression, nor is the value too small. Unfortunatley there are a lot of engines in this hobby where "artistic license" overpowers good design and performance suffers immensely because of that. a 2 stroke engine, whilst a very simple machine, is also quite complext to get all elements to balance in the Rev range where the power is required.

unit53

just to keep it within laymens terms,,,,remember ,i used the analogy of th fake rolex ? as un-technical as the statement was ,,regarding artistic license over powering good design,,hit home for me,,,and i have first hand experience.

Antique

My Feedback: (4)

Not entirely true...I cut the crank webs completly off the twin crank on two different 2 stroke engines, a GT80 ahd and a Herbrandson 289...Only difference isnperformance before and after was faster spool up, no change in power or vibration level....
Your results may vary.....

PlaneKrazee

My Feedback: (14)

Ralph,

Doesn't the GT-80 have intake ports on the cylinder with a manifold to each with a single carb? How is the Herbrandson intake set up?

unit53

my case appears well stuffed,,i dont think this is or has been an issue with the current design,or the original either.

Super08

My Feedback: (2)

Have you run it yet and how does it look?

PlaneKrazee

My Feedback: (14)

Take another photo at BDC.

unit53

because there needs to be refinements or just go back and use proper qc on the original design ,,this one ran poorly due to air leaks,,tommy says he has several,,good performing examples running but mine had the following issues ,,,,,the cylinder attachment needs to be done in a manner that allows secure tightening,,as you will see there is no credible way to get a wrench around the current setup,,instead of o rings to seal case flanges ,simple well made gaskets should have been used the o rings can remain but cannot be relied upon,,also theres a phenolic plastic type spacer used under the front cylinder,maybe to add to the sealing aerea for the cylinder to case ,that should be probably aluminum and made to fit ,,this also causes me concern of failure,,so bottom line ,,i wasnt willing to tinker with something ,,that should have worked right away ,,i transferred my parts back to my original case ,,,have flown several times since,,,tommy also suggested i use o rings to help create a cylinder/ case seal ,,but without a groove cut in either to capture an o ring,,i could not even fathom that working.

unit53

cant do it pk,, the reason is its all back where it came from,,,in its original case and running fine,,but i will share this tidbit,,,when all parts were on the new case my crank hit the bottom of the cylinder shanks where they protrude into the case,,,i had to flat grind and chamfer each cylinder tto get clearance also had to redrill each cylinder mount hole to 5.2 mm to accept to poorly designed stud,and locknut setup,, which would not worrk and i didnt trust.

Antique

My Feedback: (4)

PlaneKrazee..The GT80 has a manifold with one carb.
The Herbrandson has a carb on each cylinder.
We don't use carbs on our race twins, just a venturi with a fuel nozzle in it...Crankcase pressure through a one way valve to the tank pushes the fuel through the venturis.....We first used a brass plate with a big hole in it to have some control over the speed, but since most of the running is at wide open, we just richen the mixture to slow it down..We can get down to about 4000 rpm that way, 12,000 wide open...K I S S rules...
On our new ZDZ 210 twin we use a little fuel pump instead of crankcase pressure, controlled by a computer program...The 210 has a custom machined back plate with a WAY bigger intake hole in it.....The 210 is so far the strongest of all our engines, 800 or so more rpm than the 289 with the same prop and about 3 1/2 lbs lighter...To say we're happy with the way it runs would be an understatement...
We're doing the same things to a ZDZ 160 and an 80 twin, haven't done any testing yet.....If the 160 runs percentagewise like the 210 the DA 150 and 170s will be looking at our tail feathers....
We estimate about 40 hp from the 210 at 9000 rpm.....

aussiesteve

The spacer on the forward cylinder is there to smooth out a running condition caused by a design fault.

There is a tendency for that cylinder to "rob" all the fuel from the case and starve the other cylinder.

I hope this is not a case of the usual "Artistic licence" being supplied and I hope it gets sorted out before it is too late.
Wasn't the market failure of the original of this engine only because of QC related issues?

PlaneKrazee

My Feedback: (14)

Ralph,

Please take some photos of those set ups! They sound really cool.

aussiesteve

Wasn't that the only real problem with the original one? - poor QC (I am being nice).

It is as if Tomy doesn't actually make the engines himself and he is relying on another company to make them for him. Why else wouldn't he be able to implement what is needed. Surely even a blind mans dead dog can see that this issue can be a death knell for his brand.


Tomy think about these questions and be truthful with yourself when you do.

Do you have control over your own destiny?
Do you rely on another person to control your success?
Is that other person totally interested ni making you successful or are they more interested in their own brands?

My advice to you Tomy - If you do have any control over your product, then do what needs to be done to make these engines work right every time. If you don't care about the engines at all, please don't bother wasting the fliers money by trying to sell to them.

unit53

hi steve what i was refeering to was pertty allways dosent equate to functional,,all of tommys engines have a degree of neatness to their appearance ,and i am under the impression that alone got engines noticed and sold,,,but lets take my mt57 ,for instance,,it had those qualities but the prop stud hole was bored off center ,,and no one ever noticed it prior to it being packaged and shipped , ,now if a competent employee ran this engine first ,no one but tommys crank supplier or machinist would have known and the problem could have been corrected at the supply level,,good well made consistent parts ,,is one aspect,,good consistent assembly and testing is the other,,see you said it as well,,, a design flaw caused the use of some type of plastic to fill the void,,,where there wasnt any design flaws in the original,,why take a good thing and make it bad?ormore complicated,,im not going to even suggest how tommy should run his buisness but will offer my opinion.and wish him well.

PlaneKrazee

My Feedback: (14)

If Tomy took the original design, lengthend the case to get a slightly thicker non pinned interconnect rod, installed a ball bearing in the rear case instead of the roller bearing and corrected tolerances and QC he would have a good engine. I know Jody said the original design was fine but feel this would be better.

Who am I kidding, Will Tomy EVER take and follow advise completely?

unit53

its been like expecting the blind to see,,,thats been my experience,, i havent heard of any rear bearing failures on the original,,and ive heard another poster say awhile back,,one dosent need to reinvent the two stroke twin,,,i like you have tried to analyse tommys shortcomings when it comes to whats being presented for the market ,and ,im still confused about the outcome ,he adressed the rear bearing issue ,in the new case ,but caused other problems ,i believe he no longer deals with the original crank manufacturer and the new style unpinned,,can be machined to work with the original case ,,im actually waiting to find out from tommy ,after c.n.y .is over,to see what his next move is,,, will he scrap this design,,or make changes ,based upon recent input? or will he take the old design and make ,,some inprovements? i can honestly sat this ...the original design ,,although not perfect,,has not had any issues besides the front bearing leak ,,every other problem i read about was related to qc in every aspect,,,from dirty insides to missing parts,one couldnt beat the price ,,for a 70cc twin?maybe pay the careful employees more and fire the rest,,i cant speak for everyone,,but i agree with pk,s statement made way back,,,i wouldnt mind paying more for a consistently good product,,,,,,buying one good costly engine cost less than two bad ones.

PlaneKrazee

My Feedback: (14)

Considering you can get a great running DLE 111 for under $650.00, a MT70 with no QC is no bargin at any price.