Repurposing batavus m48 reed block

The stock reed block on the M48 Laura found in Batavus mopeds comes with stainless steel reeds. There are many reasons to switch to composite material reeds (insert reasons or link here). This is a tutorial on how to reuse the old block and install your own custom reeds to hopefully save you some money!

Before You Start

Noticeable improvements in performance can be gained from upgrading reeds in an old reed block from stainless steel to a composite materials. The way the reeds are secured on the stock M48 Laura reed block isn't the best for the DIYer looking to squeeze some power out of their moped on a budget. A solution is buying an external mount to get your own reed block on the engine, buying new old stock, or buying a re-machined one that might fit some small modifications. There is however, a fourth way which involves drilling into the rivets on the stock reed block, cutting your own reeds out of reed paper, and slightly sanding down the edges on the crank case hole to fit it all together.

Not to worry the process isn't as invasive as you might think, and I've tried to write this tutorial to be viable with the most minimal set of tools possible. Worst case scenario you mess up a reed block you were gonna throw away anyway!

That being said, make sure you have the basics:

- Cordless drill

- Drill bit set (we only used a 3/32 size bit for this project)

- Small set of files AND OR a Dremel with a cylindrical metal sanding bit

- Gasket paper

- Reed valve paper. I used carbon fiber with a 0.3 mm thickness

- Scissors and an exacto knife or similar

- Threadlocker. I use blue Loctite Threadlock

- 4 round head machine screws although countersunk screws would be better. We used M8x8mm Round Hex Machine Screws.

Modifying the reed block

First step is to drill into the rivets securing the reeds and reed bracket to the block using a drill bit that is just a little smaller in diameter than the machine screws you'll use. Take care not to damage the old reeds if possible and try to drill in the center of the old rivets so you can re-use the old bracket to hold the new reeds in.

Carefully drill holes into the rivets and check to make sure the diameter of the machine screws will be tight enough to hold.

once you've drilled the appropriate holes you could tap them with a tap and die set to make the machine screws go in cleaner, but I was able to get away with just screwing them in as is with a little Loctite in the threads.

Make sure the machine screws are a short enough length to be flush with the inside of the reed block to prevent a disturbance in the airflow. If not sand them or cut them down to the appropriate size. The length should be 4 mm. Mark the screw and sand it down to size if its longer than that.

A belt sander can be used to sand the bolt down to the correct length after marking it at 4mm.

Cutting and mounting new reeds

Grab your reed paper. Here I used a carbon fiber sheet from Treatland that's 0.3mm thick. Use the old reeds to trace an outline on the reed paper to the appropriate size and mark the two holes you will need to drill into to mount onto the reed block.

Cut the reeds with an Exacto knife or a good pair of scissors. I used scissors here since I opted for a single reed flap per side. If you try to copy the original shape of the stainless steel reeds you may need to cut more precisely with an Exacto knife.

Once the reeds have been cut grab your drill bits and cordless drill to make (insert size here) holes into the reeds. Take care to do it slowly and with little pressure as to not damage the reed paper since a tear will make it perform poorly!

Install the new reeds and make sure to use blue Loctite on the threads when tightening it all up.
Using original reeds to trace new reed on gasket paper.

Fitting it to the crankcase

Given the extra size the reed block gains from the machine screws you have now mounted, you will have to sand down a few little recesses into the crank case opening for the reed block. Not to worry! If you used small round headed screws like I instructed, you shouldn't have to remove too much of the crankcase and a perfect seal can be maintained if you choose to buy a stock or aftermarket reed block that fits how its supposed to.

Use a round mini file or the rotary tool such as a dremmel with a cylindrical metal sanding head to sand down 4 corners on the crank case hole. You can do this by eye. Simply place your modified reed block up to the crankcase hole, noting where the screws are and how much clearance they need and slowly start sanding a space for them, occasionally checking with the reed block to see if you have enough clearance. once the reed block is able to sit flush with the crank case opening, you're set for the next step.

Use a piece of a rag or plastic to block off the opening into the crank case. This prevents metal shavings from going inside and potentially harming the internals!
Here I'm using a Dremel to make the recesses into the crankcase opening to fit the new reed block and its mounting screws
This is what the final product should look like. Be careful not to overdo it. Try to fit the reed block often to check your progress so you only have to sand the bare minimum to fit.

Finishing up

Cut a new gasket to fit into the crank case side, noting that the inner hole will have to be slightly larger due to the increased size from the machine screws. Place the new gasket on the reed block and install like you would the old reed block.

Recut crankcase side gasket using some gasket paper (or cereal box cardboard). This will have to be done to fit the bigger reed block profile.

Keep an eye out for any gas leaks or a visual sign that you haven't given the reed block enough clearance to sit tight on the crankcase hole. If there's a gap it will affect crankcase pressure and the moped will perform poorly. If you notice a negative change in performance go back and make sure everything is sealing properly.

Everything mounted like nothing ever happened!

Good luck and have fun!