[Bullet Whisperer]

I think it's best to go 'open forum' on this one, rather than P.M.'s, so here goes ...
 I have been asked about my top end modifications to boost the C.R. to 9.2:1, using the standard parts.
 The piston crown needs to be machined inwards across the top from the outside edge by 10mm radially and to a depth of 2mm. This should leave a raised portion of the original top face of 64mm diameter and 2mm deep.
 Originally, the piston crown should have come up flush to the top of the barrel at tdc, the 1mm thick head gasket giving the 1mm squish clearance required. If the 2mm deep cut is made on the piston crown, it follows that 2mm needs to come off the bottom of the barrel to restore the original 1mm clearance with a head gasket. 2mm will also have to come off the bottom of the liner, or it will touch down on the flywheels.
 If for some reason, the piston crown came up higher [or lower] than the top of the liner before hand, this is the time to put things right and get the required 1mm clearance with a head gasket in place.
 I have personally 'done' two machines in this way and funnily enough, the owner of the second one called in today to tell me how happy he was with it.
 To anyone 'having a go', please follow the above advice and ask questions here and I will try to help, but I can't be held responsible for mistakes made by others trying to emulate what I have done. If you do what I did, to the letter, all should be well, if not, it might go horribly wrong, so please take time and care with whatever you do to your machines.
 Thanks,
 B.W.

[ace.cafe]

So, if I understand correctly, you are machining the 2mm thickness off the edge of the piston to create a small "dome" in the middle which fits inside the perimeter of the existing combustion chamber shape.
Then you are re-establishing the squish gap at the piston edges by removing the same 2mm amount of metal off the base of the barrel, and 2mm off the bottom of the barrel liner, so that the new top edge of the piston comes back up to the top of the cylinder bore and everything clearances okay.

The results being proper squish gap, increased compression ratio, and enough piston-to-valve clearance.

[Bullet Whisperer]

That is correct, Ace, but I feel I am having difficulty getting that across to some who want to try this for themselves and I am starting to worry that mistakes might be made as a result.
 I have received some P.M.'s relating to this, but as the questions are similar, I feel it is better to explain here, 'in the open', so to speak.
 B.W.

[Adrian II]

Hi B.W.,

from our previous conversations I understood about the 2mm deep by 10mm wide band machined off the piston crown and the 2mm off the cylinder base flange and liner to compensate, but I hadn't picked up on the importance of the 1mm clearance for the squish band. If my Redditch AVL ever gets the B.W. treatment it will need about 0.5mm off the top of the barrel before it even gets anything else done. It just shows the importance of understanding the WHOLE job. Perhaps you should market a set of drawings so you at least see a bit of a return on all your input!

As my poor old Electra might be in need of an engine rebuild it could well be time for ASBO AVL No. 3! (Still thinking about a Fireball AVL for the new project - nice to have a back to back comparison - if only my other bikes would stop sulking mechanically.)

Regards,

A.

[ace.cafe]

The last AVL head gasket that I saw was .075" thick! Almost 2mm thick. I think it was the Cometic composite gasket.
To get proper squish gap with that gasket, you'd need to have the piston coming up above the deck.
So, it is good to pay attention to the thickness of the head gasket that you are going to use, if you plan to set squish gap with it.
As B.W. points out, .040"(1mm) is a good target for a squish gap.

[AVL Power!]

Thanks for the post Paul.

The problem is most of us, including people who are working on my Enfield are working in different organizations, even tho we are enthusiasts. Most of us who work on these sort of things usually get to meet during weekend so it's pretty tough to know what's really going in there. I will still try to get there and see what's happening. According to the mechanic who did the Bottom and Top end assembling, there is a loud ping from idle till the mid range. He started the motor to check if it runs fine. They did mention there ther's no clearance issue.

In my case I did machine 2mm off the barrel and liner from bottom. The piston's 64mm center was left stock, rest 20mm was machined and stepped down by 2mm compensating the barrel's 2mm loss. But the problem is probably with the Gasket as I don't know how thick it is.

Do you think we could use a Solder wire 2mm thick  and see how much the piston to head clearance is?

Worst case scenario, I will buy another barrel and piston and try it on that once again. This time I will ask for Tej's help and work it out.

[ace.cafe]

Thanks for the post Paul.

The problem is most of us, including people who are working on my Enfield are working in different organizations, even tho we are enthusiasts. Most of us who work on these sort of things usually get to meet during weekend so it's pretty tough to know what's really going in there. I will still try to get there and see what's happening. According to the mechanic who did the Bottom and Top end assembling, there is a loud ping from idle till the mid range. He started the motor to check if it runs fine. They did mention there ther's no clearance issue.

In my case I did machine 2mm off the barrel and liner from bottom. The piston's 64mm center was left stock, rest 20mm was machined and stepped down by 2mm compensating the barrel's 2mm loss. But the problem is probably with the Gasket as I don't know how thick it is.

Do you think we could use a Solder wire 2mm thick  and see how much the piston to head clearance is?

Worst case scenario, I will buy another barrel and piston and try it on that once again. This time I will ask for Tej's help and work it out.

Yes, you should check the piston-to-head clearance. For the increased compression that this mod produces, having the squish working correctly will be important.
Ths fuel is probably going to need to be the high octane rating type, such as 98 RON, anyway.
It would be a very good idea to do a compression test, too.
If it is pinging on no load at lower rpms, there is an issue, and you may need to retard the ignition timing with Paul's box that he developed for the AVL.

[Bullet Whisperer]

Do you think we could use a Solder wire 2mm thick  and see how much the piston to head clearance is?

You could do that, I usually go for 1.5 mm thick solder wire for this purpose as it is easier to coax the piston over TDC if the clearance happens to be closer to 1mm than you might expect. Whatever you do, don't force the piston over TDC, but just keep some steady pressure on and allow the solder a little time to conform. This way, there should be no risk of damage. If it won't go over TDC and just locks up, you have too little clearance. If it goes over TDC with little or no resistance, then try the 2mm thick solder wire.
 B.W.

[AVL Power!]

@ Tom - Yes, I did talk to my friend. Once he's back, we will do a compression check. I remember last time my stock setup had more cranking compression. It was around 158psi, so I think I am on the higher side.

@ Paul - Thanks Paul! I will try this out and see the clearance.

Will keep you guys posted.

[armando_chavez]

just a thought, how come dampking says he machined 20mm radially and BW says you only have to shave 10mm radially by 2mm down?

[AVL Power!]

I meant outer 20mm, didn't say radially

[TejK]

just a thought, how come dampking says he machined 20mm radially and BW says you only have to shave 10mm radially by 2mm down?

He means turning on a lathe and turning down by 10mm from the outer edge. In my bike I turned it down to 11.5mm as there were some interference issues where the piston dome was touching the head casting. I have never had any issues with pinging and I made sure the squish was within tolerance (< 1mm). Additionally, the only time i had some pinging was on opening the throttle when riding 2 up, going up a slope in a high gear an low speed.

@Sanket : As i understand your problem is pinging from idle to mid range.

Apart from the timing, carb settings - also check if the valve seats and valves sit proud on the port - that could also potentially bump compression higher that you intended to. There is huge variation between the castings that I have seen.

 In any case if your bike had about 158 psi of compression statically when stock , did you check how much the other stock bikes have ?? Somehow that value seems a tad high for stock and the piston mod may have bumped the comp to a all new level !

[AVL Power!]

Tej - My motor had 158 psi stock when others has around 150. I remember Basanti reporting the same. Another friend has around 148 psi.

I still need to check the current cranking compression, maybe this Saturday.

[TejK]

I think as you are not working on the bike yourself and relying on other to do the right mod - I would suggest checking all measurement with a GOOD vernier which is accurate on all cuts made. ( I am saying this knowing the quality of machine shops here in Bangalore as when I did the mod I had to use the lathe my self and used my own measuring tools to get the tolerances right).

Am sure other here maybe able to suggest suitable solutions for the ping. The master 'BW' could prob shed some light on this ASBO not acting right !

Did you try 91 OCT gas for the bike and see if it runs alright ?   

[AVL Power!]

Tej - I am sure measurements didn't go wrong. Prashant himself got it done from a place where do stuff for aerospace, they're known for their work. But I will still get the entire thing re-measured. Anyways, I have ordered another block and piston, dad's bday gift to me

So I will re-do the mod on that new barrel and piston if this doesn't get sorted. I am not giving up on this I have waited enough and it's time to get it done right.

Also, I wasn't using any good grade fuel. The mechs there just wanted to start the machine and hear it run. So i will get 91 octane when I go there.

[ace.cafe]

If you are going over 158 psi reading on the compression test, it is crucial to have the squish working well, because that will be the only thing that will help prevent detonation at that kind of compression.
And you will still need high octane fuel.
91 ain't going to cut it.

And Sanket, I know that pictures can be deceiving, but that cut on the top of your piston looks like more than 2mm to me.
Have you measured that?

[AVL Power!]

I measured and marked it for them and left, need to re-measure it. Now that I compare my pics with BW's piston mod's pic. I think I went wrong somewhere. Which is a bad news! Still need to confirm.

[AVL Power!]

So from my understanding. Lets say that the deep cut on piston is now 3mm instead of 2mm, (Assuming). So in that case I need to shave my barrel 1mm more since it was 2mm before and also shave the 1mm of the piston's center crown right? To get the same compression ratio as BW mentioned? is this the only way to correct this mistake?

I am anyways getting a new barrel and piston kit so it should be fine if this one goes wrong.

[Bullet Whisperer]

Hi Sanket,
 The important bit is to have the new outer circumference of the piston crown, which has been machined, coming up flush with the top of the liner at TDC. If you have 3mm of 'original' piston crown standing proud, the C.R. will be around 9.5:1 or maybe a little more and will probably be too high for some fuels. Whatever amount has been taken off the piston crown in the vertical plane, be it 2mm or 3mm, the same amount needs to come off the base of the barrel and bottom of the liner - assuming the original flat of the piston crown came up flush with the top of the liner at TDC before any modifications were made. For example, if the piston crown was down the bore by 0.5mm at TDC, then you would want 2mm off the piston crown and 2.5mm of the cylinder base and bottom of the liner and so on.
 If you end up taking 3mm off the cylinder base, make sure your pushrod adjusters will be able to close down by a similar amount, I know they will screw in to reduce by 2mm but not sure how much further they will go.
 B.W.

[AVL Power!]

UPDATE -

Finally Saturday! and I had to time to go see the bike. A lot of things happened and a lot of confusion made things worse but in the end it all ended good, things went the way we planned

Paul - S cams made all the difference! and the compression bumping worked great. No Ping at all! Motor idles well, revs build real quick and goes higher and higher. Don't have the tacho yet but very soon.

About the Ping story - The guys who worked on the bike, are on other motor rebuilding projects so someone had to inform my friend about the bike's status, so the guy who had no idea about Enfields, started it and informed my friend what he heard and he heard the loud tappets and couldn't distinguish between knocking and the tappet notes and then came the whole bunch of wrong info from his end. (The loud tappet's noise being Pinging!)

The moment we started the bike we figured why that had happened so we made few tweaks and she runs really well now! 2nd gear and I could pull till 70kph and still had loads of throttle left! I am loving the cams!

[DanB]

Yes!  It's about time! 

Now you need to get out and ride to share with us!

[ace.cafe]

I'm happy to hear things worked out okay!
 

[AVL Power!]

Dan - Yes, few more work left, once done I will record a speed run video.

Tom - Yea, I was really worried about this whole thing a Ping was never included in my plans, luckily it's all good now. She really pulls like a train in lean settings, going more rich like BW said.

[High On Octane]

........She really pulls like a train in lean settings, going more rich like BW said.

Your bike will produce slightly more power with lean conditions, however, running lean is also a really good way to seize your motor.

[TejK]

Your bike will produce slightly more power with lean conditions, however, running lean is also a really good way to seize your motor.

+1 . Ask me how i know !!

Great Sanket !! Whew ! Good to know it's sorted ! I think you meant 'Built like a Gun, goes like a Bullet'

[Bullet Whisperer]

UPDATE -

Finally Saturday! and I had to time to go see the bike. A lot of things happened and a lot of confusion made things worse but in the end it all ended good, things went the way we planned

Paul - S cams made all the difference! and the compression bumping worked great. No Ping at all! Motor idles well, revs build real quick and goes higher and higher. Don't have the tacho yet but very soon.

About the Ping story - The guys who worked on the bike, are on other motor rebuilding projects so someone had to inform my friend about the bike's status, so the guy who had no idea about Enfields, started it and informed my friend what he heard and he heard the loud tappets and couldn't distinguish between knocking and the tappet notes and then came the whole bunch of wrong info from his end. (The loud tappet's noise being Pinging!)

The moment we started the bike we figured why that had happened so we made few tweaks and she runs really well now! 2nd gear and I could pull till 70kph and still had loads of throttle left! I am loving the cams!

That's very good news, Sanket, enjoy your bike - it should be a lot more fun now!   
 B.W.

[AVL Power!]

Tej and Adrian- Thanks a ton for helping me with all the information! I was really worried when I heard about the ping

Paul - Like you said it before, it really pulls like a train!! Needle is at 3rd slot, I will move it to 5th I feel that after this mod the motor is running on leaner side but I never run dangerously lean so I am safe I believe. Will share details on Acceleration and top speed as soon as possible.

[AVL Power!]

Paul - I had a doubt. I think I am going 535cc for now as the barrel needs to be bored, I can get a new set of 500's barrel and piston but before that I wanted to try out an 87mm piston with your squish mod. That is keeping center 64mm stock and shave down rest 20mm by 2mm. Do you think it's worth the shot?

Here we don't get oversized pistons for AVLs so 87mm is the only way for us to go bigger bore.

Regards,
Sanket

[Bullet Whisperer]

Hi Sanket,
 Yes, that should work for the 87mm piston just the same as for the standard one.
 B.W.

[AVL Power!]

That's good news for me!

Thanks Paul!

-Sanket

[Adrian II]

Sanket, glad it's all doing the business at last, is this still on the 34mm carb?

A.

[AVL Power!]

Yes Adrian, I am running a VM34. I talked to few old timers here, mostly racers who used Amals back in the days and still using Amals on their Iron barrel 500s and they are swearing by the MKIIs. So I guess I will get an Amal 36mm like BW used on his Asbo11.

-Sanket

[tooseevee]

The last AVL head gasket that I saw was .075" thick! Almost 2mm thick. I think it was the Cometic composite gasket.
To get proper squish gap with that gasket, you'd need to have the piston coming up above the deck.
So, it is good to pay attention to the thickness of the head gasket that you are going to use, if you plan to set squish gap with it.
As B.W. points out, .040"(1mm) is a good target for a squish gap.

            Do I remember correctly, Ace, (without looking back) that you shaved my AVL head by .020"?

[ace.cafe]

            Do I remember correctly, Ace, (without looking back) that you shaved my AVL head by .020"?

I don't think so.
As I recall, you measured the piston topping out at about .015" above the deck of the barrel. The .075" thick gasket will crush to some extent, probably at least .010". So that left a squish distance of around .050", which is within a reasonable spec for squish, and we needed some room around TDC for that big intake valve to clear the piston, so I think we left it at that. And you ended up with something like .032" piston to valve clearance, IIRC, and that is as close as we ever like to run it, so you shaved it all as close as was possible.
You got your compression bump from the modified chamber shape.

[SteveThackery]

Just slightly off topic.......

Ace (or whomever knows), am I right in thinking that one easy way to raise the CR on the UCE engines is simply to fit the Electra X piston?

I'm sure I read it somewhere but I can't find it in the forum.

[ace.cafe]

Just slightly off topic.......

Ace (or whomever knows), am I right in thinking that one easy way to raise the CR on the UCE engines is simply to fit the Electra X piston?

I'm sure I read it somewhere but I can't find it in the forum.

If it is a flat top piston, then yes, that can work..
However, pistons are not drop-in fit, unless you are unusually lucky, and will require honing in the best case, or if it is too small it will need the next oversize piston and rings.

The "easiest" way is to use a thinner head gasket, and/or a thinner cylinder base gasket, and measure your distance between piston and head at the squish pad areas. In other words, bring the piston closer to the head at TDC, but no closer than .040"(1mm) .

[SteveThackery]

Thanks, Ace.  So is the normal UCE piston dished, then?

[ace.cafe]

Thanks, Ace.  So is the normal UCE piston dished, then?

The ones I have seen are dished in the 84mm bore 500.
I haven't seen the 87mm piston from the GT yet.

[AVL Power!]

TejK is already using the 535 GT piston which is dished out I think.

Here's a link - http://www.enfieldmotorcycles.com/forum/index.php/topic,20622.0.html

Earlier, few bikes in India, that is Continental GT which came with Wossner's 87mm flat top pistons but later they got the home made crappier versions of the same for much cheaper price. Pistons are not bad but I am assuming they are inferior than Wossner. I might be wrong too

-Sanket

[Adrian II]

TejK also noted that the Wossner pistons were heavier, which might put some people off.

Exactly how deeply are the factory 535 GT/UCE piston crowns dished?

Regards,

A.

[AVL Power!]

Yep they are very heavy, when compared to stock 84 or even 87mm pistons.

About the dish - I am not sure but I can try measuring it in the garage.


-Sanket

[High On Octane]

The "easiest" way is to use a thinner head gasket, and/or a thinner cylinder base gasket, and measure your distance between piston and head at the squish pad areas. In other words, bring the piston closer to the head at TDC, but no closer than .040"(1mm) .

I just did this with my twin.  My cylinders pressures were around 125psi.  Me being the sporty guy I am, wanted more without spending money.  I knew I had about 1mm to work with before my piston came to the top of the cylinder deck, so I removed all the base gaskets and put a thin layer of hi-temp silicone on the base of the engine case, assembled the top end with .059" composite head gaskets and let it cure overnight before attempting to start.  I now have about 150psi per cylinder as just tested this morning.