[eda1bulletc5]

Hi Folks,
I have my UCE engine opened up and would like to get some suggestions on the two options that I have as upgrades (only these 2 due to budget!)

1. Change the stock piston head to 500cc AVL; AVL is flat head and thus the compression increases, and hope is it will have some improvements over the stock (or)
       --  I already have the AVL piston and rings for this
2. Change the cylinder barrel and piston to a 535cc. The stock 535 piston head is a dished kind (same as stock 500)
       -- relatively expensive, but is within my budget.

Which one would give me good torque and a decent increase in performance across the rev range?

My bike already has the following mods;
- Aftermarket mild cams, ACE intake + high flow exhaust and Power Commander V w/Auto Fuel Controller and tuned

Any input greatly appreciated!

Have a great weekend!

Sajiv

[ace.cafe]

I suggest AVL flat top piston, and do the "squish mod" by shortening the barrel exactly enough to allow the top of the piston to be even with the top of the barrel at TDC. Then use the 1mm thick head gasket to set proper squish distance.

Be sure to check that the valves to not touch the piston at TDC.

This gives a nice increase in compression which will help a lot with torque and will help out those cams you have.

Also, it's cheaper because you already have the parts. Changing to 535 barrel requires machine work on the engine cases, and requires new parts to buy.

[eda1bulletc5]

Hi Ace,
As always thanks a lot for your suggestions!

I will use the AVL pistons then and maybe do the "squish mod" later...

[gizzo]

I will use the AVL pistons then and maybe do the "squish mod" later...

Why not do it now? While you have the barrel off anyway? It's only a quick job at the machine shop...

[eda1bulletc5]

Gizzo,
Yeah, that is a good point.

I have to find out a good engine shop local to my town.

Ace / Gizzo,
what exactly entails the squish mod? It seems to get the barrel shortened, the top of the barrel needs to get ground such that the top of the piston head during TDC is flush with the top of the barrel
But beyond this how to perform the proper squish distance?

Thanks,
Sajiv

[AzCal Retred]

Here's a good explanation of squish. Soft clay or wax can be useful too in getting actual measurements.

https://en.wikipedia.org/wiki/Squish_(piston_engine)#:~:text=Squish%20is%20an%20effect%20in,mm)%20to%20the%20cylinder%20head.

[ace.cafe]

Gizzo,
Yeah, that is a good point.

I have to find out a good engine shop local to my town.

Ace / Gizzo,
what exactly entails the squish mod? It seems to get the barrel shortened, the top of the barrel needs to get ground such that the top of the piston head during TDC is flush with the top of the barrel
But beyond this how to perform the proper squish distance?

Thanks,
Sajiv

The thickness of the head gasket sets the squish distance. That's it.
Use the 1mm thickness head gasket.

[manxmike]

A friend of mine used to use plasticine to set up squish distances when he was working on classic Ducati racers. It always seemed to work for him.

[tooseevee]

A friend of mine used to use plasticine to set up squish distances when he was working on classic Ducati racers. It always seemed to work for him.

   Yes. I think it was called Plasti-Gage or something similar.

    I just used clay when I checked after the AceHead work. Worked fine.

[eda1bulletc5]

What is the normal height between the piston TDC to the edge of the barrel? In my enthusiasm to get the cylinder head + cylinder barrel to the shop - I forgot to get the measurement ...

I am wondering if there is a range of measurements that have been observed...I was thinking about asking the shop to reduce the cylinder barrel by 1mm (0.040").

Please let me know; thanks in advance.

[ace.cafe]

What is the normal height between the piston TDC to the edge of the barrel? In my enthusiasm to get the cylinder head + cylinder barrel to the shop - I forgot to get the measurement ...

I am wondering if there is a range of measurements that have been observed...I was thinking about asking the shop to reduce the cylinder barrel by 1mm (0.040").

Please let me know; thanks in advance.

Ya gotta get it back, and do the measurement of piston below top of the barrel with either the cylinder base gasket in place, or without, depending on how you plan to do final assembly on the engine.
This is not a "ballpark" sort of thing.

[Crispyduck]

I used a piece of 2mm diameter soldering lead to check the squish on mine. Make sure you get the soft type so it crushes fairly easily.

I'm no expert but it seemed to work well and u can measure it afterwards with a micrometer without easily squishing it further and then getting a false reading.

[eda1bulletc5]

Thanks for the replies!!! As always appreciate the support and guidance!

Here are some pictures of the piston at TDC; without the bottom gasket; it is pretty much flush with the top of the cylinder barrel.

The bottom gasket (composite) by itself has a thickness of ~0.040"; the top Multi-Layer Steel (MLS) gasket is ~0.030" at its thinnest part.

So if shorten the barrel by ~0.030" it should provide a squish gap of ~0.038 to 0.040". Does this sound about right?

Of course, once I have the cylinder work done and then put it all together I can actually measure this gap using a 2mm soft solder.

[ace.cafe]

As long as you end up with about 1mm squish distance, you can take any necessary route you want to get there.

[Crispyduck]

Don't forget about the thickness of the head gasket. If I'm not mistaken the squish is the distance from the piston crown to the top of the cylinder plus the head gasket thickness in its compressed state. Better to measure the squish physically though i think. Its not something u want to get wrong.