Green Tanker Build

[mercaholic]

I was sorting thru my parts bin to come up with this winter build.

Does anyone know if this combo of parts will bolt up or/and has anyone tried this ?

- KG4 (early) crankcase
- Mk20 cylinder block (ported exhaust)
- flat-top pistons from a Mk35A  
- Mk20 carb converted to gravity feed

My plan is to mount this on a fishing KG7 tower.

[TNT Teen]

I don't see why that wouldn't work. Using the ported block, might as well use a bigger carb if you can.

[mercaholic]

I'm now realizing that the KG4 rods are somewhat unique such that fitting in a later piston design may pose a challenge getting the correct side clearance of the piston pins.

However, I will figure something out to make it work as I am looking forward to see how it breathes and if the extra compression will be noticeable.

[Fastjeff]

If they are like the later 20/ 22 cube parts, the difference in weight (of the two different diameter pistons) is taken up by fat aluminum washers at the wrist pins on the 20 cubers, and thin steel washers on the 22 cubers.  This way Merc could use the same crankshaft for both motors without special balancing.

Jeff

[mercaholic]

Struggled to get the correct piston pin washers (spacers) clearances and got it bolted up.

Lots to keep going on this.

Question:  were there flat top pistons available for the KG4/KG7 race blocks?

[rumleyfips]

There were flat top pistons for the KG4/Mk15/Mk30 engines. 20 inch flattop pistons were produced for the 20H/55H . They would fit the KG7 but it was out of racing by then.

[Fastjeff]

See that fat washer he's holding? That's the additional weight used to allow lighter, smaller diameter pistons to use the same crank. The larger bore pistons use thin steel washers that are lighter to maintain the balance.  Pretty slick!

Found all this out building my Mark 78 when I tried to install Mark 75 pistons.  Doh!

Jeff

[mercaholic]

Jeff, with slightly heavier pistons from factory and the large washers all around, can I expect any balance issues for this block ?

[Fastjeff]

You could weigh the parts a do a bit of careful metal removal.

Jeff

[zul8tr]

Struggled to get the correct piston pin washers (spacers) clearances and got it bolted up.

Lots to keep going on this.

Question:  were there flat top pistons available for the KG4/KG7 race blocks?

What pin washer side clearance did you use  

[mercaholic]

Struggled to get the correct piston pin washers (spacers) clearances and got it bolted up.

Lots to keep going on this.

Question:  were there flat top pistons available for the KG4/KG7 race blocks?

What pin washer side clearance did you use  

Just a few thous, enough to allow a small amount of lateral movement.

[mercaholic]

Installed the mk20 carb but now limited the advance by the fuel feed on top of the card.

[mercaholic]

Tank tested yesterday while the temps allowed.

I only ran it for half an hour to ease the break-in but still very tight.  

Compression is up to 110# on No.1 but only 104 on No, 2.

It sounds a bit more throaty but will need to wait until the spring to wring it out on the lake.

Note the ether can in the background.... .  Luckily I did not have to use it.

[SteveC]

Installed the mk20 carb but now limited the advance by the fuel feed on top of the card.

On my "Greased Lightning" project, that has a lot of alignment with your build here, I tackled this problem by moving the fuel inlet tap to the side of the carburetor cover and plugged the inlet on top.  I had plug a vent hole on the inlet I tapped, but this allows the throttle handle to make the full travel.  

Steve

Hopefully I can get some photo's up to show you what I was doing.  I am using a Mk-25 barn door case, so it has the fuel pump boss on it, so I am planning to use a fuel pump anyway.  The tank will just be there to hold the recoil and look nice....

[Genel]

Steve I would also like to see how you modified that carb. I would like to convert this one.

[mercaholic]

Likewise

[outboard315]

viewtopic.php?f=17&t=14625&p=117172&hilit=Gravity#p117172

viewtopic.php?f=17&t=13668&p=108453&hilit=Gravity#p108453

Here is a couple of threads where the conversion is explained.

[SteveC]

We have been traveling back and forth to the hospital for the last several weeks, so I have not had much time to work on the motors.  I hope to get a photo up soon.

Steve

[JW in Dixie]

I have run both Mk20 and 25 stock carbs on gravity feed - no problem. Good luck with the motor and the health. JW

[chuckw]

Can anyone post pics of the conversion, specifically the hole for the fuel shut off valve and what it looks like in the inside of the float bowl. . I am going to convert an AJ47A to gravity feed. What tap size do you use? I have two shut off valves, one from an AJ32A and another from a KE7 ( I think). Which one gets used? Or can I use either one? Thanks for the help.

[champhotrod]

I have converted several pressure fed carbs to gravity feed. Use an
AJ47A or similar carb as the newer carbs have a better idle circuit. Had to buy a special tap for the bottom of the float bowl hole.

[Bob]

I have a dial compression tester, what type do you use to be that exact 110 and 104 ?
Thanks
Bob

[SteveC]

Sorry it took so long to get some photos of how I modified the carburetor cover to give me clearance for the throttle lever.  

What I did was to tap 1/8" pipe thread into the side of the cover where the vent hole is drilled.  I then added a new vent hole through the top of the cover, and put a flush mount pipe plug into the original top inlet.  I then drilled a hole from the new inlet to the center cavity above the inlet needle.  Then finally, I plugged the original vent hole from that inlet so the fuel would have to go through the needle/seat assembly instead of going through the vent hole.  

When installed, the throttle lever can pass above this for full travel.  The fuel hose will pass from the fuel pump and under the backside of the carburetor and up to the new inlet location.

Steve

[SteveC]

I posted photos of the installed carburetor in the FrankenMerc section.   viewtopic.php?f=64&p=130831#p130831

Project "Greased Lightning"

Steve