A35 base spacing

At bottom dead center the transfers are partially blocked. Has anyone base spaced their cylinder? Is there any benefit from base spacing or will the port timing just get thrown off?

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Re: A35 base spacing

I cut the piston, which is probably a dumb idea so I'm not recommending it.

Re: A35 base spacing

you cut the piston down at the transfers? How did it perform? Was it worth the trouble?

Re: A35 base spacing

i do the same, takes 5mins max

Re: A35 base spacing

> Alex hernandez Wrote:

> -------------------------------------------------------

> you cut the piston down at the transfers? How did it perform? Was it

> worth the trouble?

I did that on a TM125 that I installed an RM125 piston in . I also changed the skirt configuration .

That turned out to be the best motor . It would perform well from idle , like a trials bike , all the way through to high RPMs . It had no problems staying with , and passing some , 250cc bikes .

Re: A35 base spacing

Great insight. its way easier to mod the piston than to base space and have to mill the cylinder and change the port durations. How did you modify the skirt PD? Shortened, shaped? Was the jetting affected? Thanks for the input guys I appreciate it(edited)

Re: A35 base spacing

I simply drilled a couple of holes in the intake skirt . I don't remember the size , but they weren't huge . It was about 35 years ago . I'm lucky to recall it at all . ;)

Re: A35 base spacing

^^ Best answer, hahaha.

Re: A35 base spacing

Chöschi21 C.K. /

I do this kind of stuff a lot, realy wouldn't recomend to mod the Pistonhead, also, if you would only go up on the Transfers you will damage your Piston and Cylinder over time because the time between opening the Exhaust and opening the Transfers would get shorter, i added an image to this post, a good tip is to Shape the parts canals that you put into the Pistons how the Ports flow.

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Edit: if you can, use a Spacer, if not just go for 115° Transfers and 150° Exhaust.(edited)

Re: A35 base spacing

^thats upside down¿¿

Re: A35 base spacing

Nice!! That Chris that’s exactly what i needed. I think i am gonna go that route.

Re: A35 base spacing

If your picture is showing BDC... you could actually add or use a thicker base gasket to space it correctly and get more flow out of your transfers....

Re: A35 base spacing

How about the exhaust port would you lower it to compensate for the spacer? I would have to also mill the head to correct the squish. Is there any advantage to base spacing over piston modding? seems like dremeling the piston might be easier.

Re: A35 base spacing

Chöschi21 C.K. /

DO NOT lower your Exhaustport timing.

Re: A35 base spacing

> Christian K. Wrote:

> -------------------------------------------------------

> DO NOT lower your Exhaustport timing.

i think he meant lowering the floor of the exhaust port, which would not affect the timing.

I would lower the floor of the ex port after you install the base spacer. it should be level with the piston crown edge at bdc.

Re: A35 base spacing

That’s exactly what i meant! Thanks.

Re: A35 base spacing

Played with different thickness base gaskets Went with .3mm. Instead of raising the bore the whole amount i needed i chose to raise it .3mm and mod the piston to match the transfers. I raised and widened the exhaust about 1mm. I didnt alter the intake port but i did open it up from the back where the reeds sit. Widened the transfers where they meet the case and modded the piston skirt. Finers crossed for this thing to work.

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Re: A35 base spacing

Still need to finish modding the piston, hone the bore and check the squish.

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Re: A35 base spacing

I just want to know where you got that cool circular port timing map? would be cool if it had blowdown too.

Re: A35 base spacing

this maybe off topic but the cylinder top needs to be cleaned up, it wont seal as is.

Re: A35 base spacing

The port map I poached from an old thread i found here on MA. Iam definitely going to sand down the cylinder and head for a better seal. thanks pat. I under estimated The work involved in bringing back a busted motor. I might have been better off buying a better condition jug maybe even a cheap kit. The way iam justifiing it in my mind is that iam recycling and saving the earth. i just hope this thing runs.

Re: A35 base spacing

> Alex hernandez Wrote:

> -------------------------------------------------------

> The port map I poached from an old thread i found here on MA. Iam

> definitely going to sand down the cylinder and head for a better seal.

> thanks pat. I under estimated The work involved in bringing back a

> busted motor. I might have been better off buying a better condition jug

> maybe even a cheap kit. The way iam justifiing it in my mind is that iam

> recycling and saving the earth. i just hope this thing runs.

Yer doin' fine . I don't know how much earth you're saving , but , better to use what you have . ;)

Re: A35 base spacing

Decked the cylinder and head used a little bit of copper spray to ensure seal. The piston rings were already gapped to big at 1.8mm so i left them alone.

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Re: A35 base spacing

With the base gasket and piston mods the ports are unobstructed at BDC. No head gasket just copper spray i got 1.03mm squish band.

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Re: A35 base spacing

and....

Re: A35 base spacing

Brandon Weiss (Detective brandon to you) /

BOOM

Re: A35 base spacing

And then... the reed valve.... the carb...

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Re: A35 base spacing

And then...Motor on the bike.

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Re: A35 base spacing

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Looks good. Seems like you put a lot of work into it. I usually cut this bridge out between the windows on the piston.

Hope that copper spray works. I always had trouble with it staying sealed. But it may have been user error.

Re: A35 base spacing

I thought about taking out that bridge in the piston but didnt cuase iam not really sure what iam doing. I did recess the bridge a little bit for clearance when it heats up. You cant really notice in the picture.(edited)

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