Speed and engine size

Michael Dufault /

Recently I spoke with a close friend of the family who is also a mechanic. For over 10 years he worked on small engines (mini-bikes, snow-mobiles, mopeds, lawn-mowers, generators, etc.). For a short time in the 1980s, he was a dealer of SACHs engines in Oklahoma.

I asked him about the 70cc performance upgrade from Athena and he mentioned that I could do essentially the same thing by putting TWO head gaskets between the engine head and the lower part of the engine. Evidently, the extra space causes the engine to be larger and therefore does basically the same thing as the performance kit, for $4.00-5.00!!!!!

He said that if I did decide to use two head gaskets that I needed to make sure that I torqued the screws correctly to ensure that I do not get any leaks. He estimated that I should be able to increase my speed by about 25% (currently ~25, I should go to ~33mph).

Has anyone out there ever heard of this? or tried this? For the price of one head gasket and a little bit of time, I think I will try it!!!! And the best part is that because I will not be putting on a new head, there is no real "break-in" period. Besides, he said that if I did not see the type of power increase that I wanted, I could always spend the money and put the 70cc performance kit on later. It is too bad that he does not live close enough to show me how to do it.

The next time that I talk with him, I will ask him if I it is possible to put on the Athena performance kit AND the extra head gasket to increase the engine size even more.

Any thoughts?

MRD

Re: Speed and engine size

That is not correct. If you increase the size of the cylinder, the piston will not compress the fuel and air as much, leaving you with less compression and less power. My removing the head gasket, you will shorten the cylinder and create more power. A speed kit gives you a bigger cylinder and a bigger piston, which work together to create more power by compressing a larger amount of fuel and air. I understand where this mechanic could be thinking from, but it makes absolutely no sense and will definetely not work.

Re: Speed and engine size

yeah .. it been mentioned here many times.

Except you have your terms messed up .. and your buddy forgot to mention one problem with his plan.

The head is what the spark plug is in.

The head sits on top of the cylinder.

There is a gasket between the head and cylinder .. its called the head gasket.

The CYLINDER sits on top of the engine.

Underneath the cylinder is another gasket called the BASE gasket.

THAT is the gasket your friend was talking about.

He is saying put 2 BASE gaskets on .. not two HEAD gaskets.

.. and .. messing with the gaskets does NOT increase the 'size' of the engine.

It advances the port timing .. (which gives more top end power .. with a little less low end power).

The other part he forgot to mention .. is that the engine will feel pretty darn slow from 0 to 10 or 15 unless you REMOVE the head gasket also.

use the 'search' button above for 'spacer plate' .. ypou will find a little more info.

Playing with the gaskets is a fun way to try some different stuff without permanently changing your engine .. or damaging anything .. try it and tell us how you liked it.

To my knowledge nobody here has ever tried it.... (cept me .. with sp. plates).

Re: Speed and engine size

.. well thats wrong .. it WILL work .. but the kid has his terms messed up .. he said head gasket but he misunderstood that his mechanic meant BASE gasket .. and that you have to REMOVE the head gasket to get back the compression you lose by raising the cylinder.

try it .. its easy and cheap

Re: Speed and engine size

As you can tell, I am rather new at this :) That is why I decided to check with the moped army. I sort of figured that I had a few things confused. Thanks for clearing things up a little.

I will check the archives for "spacer Plates". Any other information in this regard would also be helpful.

Thanks

MRD

Re: Speed and engine size

Michael Dufault /

Fred,

I read the strings about spacer plates. Thanks for the info, but I still have a few questions if you do not mind?

1) If I were to use two base gaskets and remove the head gasket to compensate, wouldn't my engine leak? I though that is what gaskets are for?

2) Are base gaskets and head gaskets usually the same thickness? If so, I should just be able to add a base gasket and remove the head gasket and be finished??? If they are NOT the same thickness, then I should be able to add a base gasket that is the same thickness as the head gasket, and then just remove the head gasket???

3) Assuming that I successfully add the extra base gasket and remove the head gasket (of equal thicknesses) will I still lose a lot of bottom end power? Can I expect to gain ~20% (5mph) on the top end?

4) If I put the performance kit on, can I still try this spacer trick? It seems to me that if I could, then the 70cc performance kit would give me both low and high end power, and then the spacer would lose low end power but also add high end power for a net effect of ~no loss or gain of low end power but a big gain in top end power?

5) Finally, if these changes are done correctly, are they safe for my engine or am I asking too much from the little guy? I don't want to ruin a perfectly good engine just because I am greedy for a little more speed.

I know that this is a lot to answer, but I would be very grateful if you could take the time to address each point. If you do, then I think it should answer any future questions the I or others might have.

Input from others is also welcome.

Thanks in advance,

MRD

Re: Speed and engine size

pretty much everyone in kzoo (as far as i can tell) who's in the moped army has removed their head gaskets. we get a bit more performance.

no one has yet tried adding two base gaskets ... which makes sense. i'll try that when i get a chance. thanks, fred!

playing with gaskets

Let me start off and say that you never mentioned what bike.

And... I assumed we were talking about motors with aluminum heads on cast iron cylinders.

If you have an alum cyl on a aluminum cyl .. then it may well leak with no hd gasket.

> 1) If I were to use two base gaskets and remove the head

> gasket to compensate, wouldn't my engine leak? I though that is what gaskets are for?

Well yes .. but .. if it is an alum hd on a cast iron cyl .. then it will work .. especially if you 'lap' the head and cyl gasket surfaces... (do a search)

> 2) Are base gaskets and head gaskets usually the same

> thickness? If so, I should just be able to add a base gasket

> and remove the head gasket and be finished???

They are usually pretty close.

> 3) Assuming that I successfully add the extra base gasket and

> remove the head gasket (of equal thicknesses) will I still

> lose a lot of bottom end power?

probably just a little bit

Can I expect to gain ~20% (5mph) on the top end?

I doubt you would gain a whole 5mph .. maybe 2 3 or 4 though ..

> 4) If I put the performance kit on, can I still try this

> spacer trick?

I wouldn't .. the designers already are giving you more performance because they knew thats why you bought it.

It seems to me that if I could, then the 70cc

performance kit would give me both low and high end power,

> and then the spacer would lose low end power but also add

> high end power for a net effect of ~no loss or gain of low

> end power but a big gain in top end power?

Maybe .. only a test will tell .. but if you don't like it .. you could just go back to what they sent you.

> 5) Finally, if these changes are done correctly, are they

> safe for my engine or am I asking too much from the little

> guy? I don't want to ruin a perfectly good engine just

> because I am greedy for a little more speed.

Good point .. and thats why I would proba leave the performance kit as they supplied it... blowing up motors sucks pretty bad.

Remember .. I was referring to Alu head on a cast iron cyl.

(running with no hd gasket)

Re: Speed and engine size

miguel wrote:

> pretty much everyone in kzoo (as far as i can tell) who's in

> the moped army has removed their head gaskets. we get a bit more performance.

>

> no one has yet tried adding two base gaskets ... which makes

> sense. i'll try that when i get a chance. thanks, fred!

remember .. if you just add the extra base gasket .. you are definitely going to lose low end .. (because you;ve already removed the head gasket) .. the only way to make up for the lost compression is to have the top of the cylinder machined off an equivalent amount.

Re: playing with gaskets

Fred,

Thanks for taking the time to address all of my points. You make a lot of sense. I think I will just put on the performance can as it is supplied by the dealer. Maybe I will try to improve the speed with a turbo exhaust if I can find on that will work.

Also, I apologize for not mentioning the motor, I though that I had. It was in another thread. Anyway, it is a Sachs 505/1B, Ausf, 47cc motor.

Thanks for all of your help.

MRD

Re: Speed and engine size

Reeperette /

>>To my knowledge nobody here has ever tried it.... (cept me .. with sp. plates).<<

Being that I can cut some of that leftover gasket material and do this mod for free.... money being tight with the new house and all... imma try this.

I will let ya know how it works on a 93 Tomos Sprint with a Stock Engine soon as I do it, too.

-R

Re: playing with gaskets

When you do this, give your results. I've been tweaking my sachs a lot, and if this works, it'd be great.

The only problem I've seen is that sachs's DON'T HAVE A SEPARATE HEAD. So there is not a head gasket, only a base gasket. That also may be why there is a little confusion on terminology.

Hell, I'd like to try it too.

There is no head gasket on a Sachs

> The only problem I've seen is that sachs's DON'T HAVE A

> SEPARATE HEAD. So there is not a head gasket, only a base gasket.

Oh geeze .. now look at that .. essentially I wasted my time replying because I didn't know what motor we were talking about.

Re: There is no head gasket on a Sachs

sorry Fred

That's why we should all say make model, year and engine when you ask a question like this.

But on a positive note, your information will help everyone, if they are willing to search for it.

For the sachs- there is no way to re-gain compression.

I think the one-piece head is why the Sachs will always be at most #3 behind Tomos and Puch.

mrd: Question?

Did you ever follow your Olkahoma friends recommendation and put on two base gakets?

mrd: Question?

No Dennis I never did to use two base gaskets. Instead, I decided to change my sprocket ratios. I will cause me to lose a little acceleration but it should improve my top end speed. Eventually, I hope to add a 70cc kit upgrade, a larger carburator and an expansion pipe to the exhaust. If I can make all of these changes, my speed should be where I want it.

MRD

Re: mrd: Question?

The gear ratio change on my sachs made a nice difference. It took very well to the gear change. I looked down at the speedo, and it was about 5mph faster than it used to be, according to engine sound. cruising speed is up to a little past 30, and I still haven't gone thru and re- tuned it.

I want to see those results when you get all your german parts on it, OK?

Re: mrd: Question?

Well, the first of the parts arrived today. But they are limited to the front and rear sprockets, new spark plugs, new gaskets, and two different size jets (stock is 50, I purchased a 48 and 52).

Since this will be the first moped that I have worked on, I decided to start with the inexpensive stuff first. Who knowns, it is possible that a good cleaning, re-jetting, and changing the gear ratios may raise my speed to a level that is satisfactory (like 28-30mph).

I have no doubt that eventually I will add the parts that I mentioned previously, but as long as I learning and having fun, there is no rush. Two other reasons why it may take a little longer than originally thought:

1) I have an 11 week old son (my first child) so FINANCES and TIME are a little tight right now. My wife wants to save money now and make the parts my Christmas gifts.

2) I am waiting for the repair manual to be delivered from the U.S.A. so that I have something to fall back on in case I screw up.

When the time comes, I will keep everyone updated.

MRD

Re: mrd: Question?

Don't forget to change you transmission fluid to Dextron, if you are still running type F. Enjoy being a father. Seems like you're going to make a very good one.

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