Sachs trials engine tuning

[3putt]

Expect to have a need for subject soon, and assume the cylinder port timing for a trials engine different from other applications.
Is this a correct assumption ?
Are cylinders for trials engines available ?
Are cylinder heads different from others ?
Are sleeves for Trials cylinders available ?
Would appreciate any advise from Sachs engined trials riders before we get started, and will thank you in advance.  3putt

wnm

[Doug Wilford]

The Sachs engine is very versitile.  The 1251/A/5 was as good as it gets in stock form.  There are no porting changes made by the factory, the engine was designed for all applications, street,and off road.  Later the "A" was converted to an aluminum cylinder and 6 gears to increase performance and HP and all the different models after that were geared for speed and performance.  Some British manufacturers used the Sachs engine for trials.  I do not believe these engines came from Sachs with any different porting or compression specifications.  It is possible that the manufacturer could have changed them?

 

[OUCWBOY]

3putt,
I agree with Doug (and who wouldn't he is Mr. SACHS) All the data I have shows the same part numbers for the cylinder, head (except the diff between alum and cast) and piston. The only difference may be the carb. I own a Woodsman, which is a modified Trials bike, only difference is the seat and pipe. My Woodsman has the same power band as the other stock Penton 125s that I own. There is no difference in the timing either. There is a Wassell expert that's a member who should have all the answers. How about it Paul?
Donny

[Dennis Jones]

3putt

I have been competing in AHRMA trials on a Sachs powered Penton/Wassell for several years now. Everything I have learned goes along with the previous posts.
My current mount ( and by far the best ) uses a 125 1/5A motor with cast iron barrel with alloy radial head. The benefit of this combo is the iron barrel can be bored to 152cc if you can find a piston. The added displacement really helps. I have been told these pistons are for a 305 Yamaha twin but I am not sure of that. An 11 tooth c/s  and 54 - 58 on the rear will get your gearing  close. Hope this helps.

Dennis Jones

[OUCWBOY]

Dennis,
Thanks for the additional comments. I too have heard that the 305 Yamaha Piston is the one to use. I remember back in 69 my dealer (Mike Lewis) and Leroy Winter converted my Six Day into a 152cc and it did make a difference in the low end power. I think Kip has a 152 Six Day also. I think my head was replaced also with a sunburst head. My Woodsman is a 152 with a sunburst head. There may be 152 kits still floating around somewhere.
Donny

Edited by - oucwboy on 07/11/2002  1:25:15 PM

[Frenfroe]

What's the bore on the 152cc kit? Do you have to change cylinders/sleeves or overbore the existing sleeve? I assume you cut the head a new squish area.

 

[Dennis Jones]

I am not sure of the bore but measuring a piston with a ruler is around 55. You just bore the existing liner to size and the head does need to be machined. I can not do this myself so I can't give any details.I need to correct my earlier post. Rear sprocket size for tials should be 64 - 68 not 50's.

Dennis Jones

[3putt]

In order of your response- Many Thanks to Doug, Donny, Dennis, Frenfroe.  After combining all the input my assignment looks fairly clear, but maybe not easy.  If the budget will allow, I will be looking for the recommended engine and 152cc kit.  Forgot to ask what size carb you use on your bikes ?  I expect to be at VMD this week and hope to catch up with all at the POG Exhibit, and maybe some additional education.
Regards,  wnm    3putt

wnm

[rob w]

FYI, The Buehner's Supply Penton Parts catalog has Sachs 152 pistons. It reads, Note: bottom of 125 iron barrels must be machined down-cast iron heads must be replaced with an aluminum short finned radial head with an enlarged combustion chamber. Keep your feet on the pegs. rob

 

[OUCWBOY]

3putt,
Most of the cast iron cylinder Sachs motors came with a 24mm Bing. Installing a 152 kit, I would increase the size of the Carb to about a 28mm. Everyone else agree?
Donny

[OUCWBOY]

Rob,
Back in about 69 or 70, 152 kits were being installed without the alum sunburst head, just had the combustion chamber machined to fit the piston. I remenmber the rod ad t be reamed out to fit the wrist pin. This was when (I think) they were using the Yamaha piston. I know 69' was one of the first ones done and they had a little trouble doing it.
Donny

[john durrill]

Donny '
 Al says he has wiesco 152 kit  pistons that have 15 mm wristpins. they would fit with out reaming the rod. the Yamaha piston used a 16 mm wrist pin. Doug told me that they had to use  100 cylinders ( cast Iron ) because the 125 cylinder would bore out into the inner wall of the transfer ports . If you use an aluminum cylinder it looks like you can bore the stock liner out and have it resleeved with out doing that. the bore on a 152 is 60 mm I think. we explored this option  when i was looking for an increase in bore for my six - days. it looks to me like you would have to open up the cases a bit and re-machine the head  to keep the compression from going up too high  and the piston from contacting the head.
 Its the same bore size as the Sachs 175 gs 6
the 175 just uses a 61 mm  stroke i think.
 you just need a good machine shop that can do the work. Its a lot of money but when you price the parts and labor on new equipment it brings things into perspective. a piston for a new KTM 200 is in the 300 range.
  Speedy suggested getting the cylinder nico sealed. that would save the cost of haveing a custom liner made. thats over 300 with the porting fome LA Sleeve.

 

[OUCWBOY]

John,
Thanks for the data. Gosh, once someone brings up a subject, it's amazing how the old brain works to kick out some of the old memories. I was right in the middle of writing that last post when I went "WOW" I remember them having to bore out the cod too. I do know that wiseco had a kit that was much easier to install, but like I said, my 69 Six Day was one of the first that was done. Look at what you've done with the 175 KTM cylinder. I think that is AWSOME!
Donny