TheSamba.com :: View topic - Simple, effective method to clean out manifold preheat risers

Mon Oct 19, 2020 5:53 pm

I'm doing some deferred maintenance on my 76 convertible and knew I needed to address the clogged state of my manifold preheat riser tubes before the weather got too cold. While I could blow a little air through mine, they were quite restricted and take a long time to heat up after a cold start. Searching this forum I found several suggestions for how to do this, including pouring vinegar in them, carb cleaner, heating, etc. None of these worked for me. So I wandered through the aisles of the local hardware big box trying to come up with something clever. Below is what I landed on, and I hope it is helpful to others. This forum has provided me with generous assistance as I learn how to work on my Beetle, so I hope I can start to return the favor.

What you need:

2 feet of 3/16" stainless steel braided cable. This cost me US $1.44 total.
A power drill
needle nose pliers
thick protective gloves, preferably leather or welding gloves
eye protection

(1) Give one end of your cable about 1/2" of frayed fibers. It should look like it had a bad hair day, like this:

(2) Insert the other, non frayed end of the cable into your drill chuck and tighten it down very firmly:

(3) Using your gloves and eye protection, start the frayed end of the cable into one end of the preheat riser. In my case, it helped to introduce a slight bend to the cable to match the bend of pipe. Manually force the cable into the pipe at least until it passes the bend, just a few inches.

(4) Now this part is important: set you drill so that it will spin the cable in the same direction as the wind of the cable. In other words, when the drill is spinning, it should be trying to "tighten" the windings of the individual cable fibers. In my case, this meant setting the drill to spin in reverse, as if I were unscrewing a screw. At no time in the process should you spin the drill in the opposite direction, or it will unravel the cable and make a huge and dangerous mess. Ask me how I know (hint, this is the second piece of cable I had to buy!).

(5) While gently guiding the cable with one hand as shown above, and holding the preheat tube securely to the floor with a foot or other heavy object, slowly start to rev the drill. If the cable starts to try to loop on itself, you're going too fast. Spin the cable, guiding with your hand and providing slight pressure in the direction of feeding the cable up the preheat pipe. The drill will do most of the forward work for you. Advance the cable until the drill chuck is close to the pipe end.

(6) You will likely need to occasionally check the drill chuck for tightness. If you haven't done so, retighten it when the drill chuck gets close to the pipe end, and certainly before starting to pull the cable out. The cable must be spinning to retract it, in my experience. Spin it (still in the same direction, don't reverse your drill) and pull gently until the cable end exits the pipe.

(7) Since a 2 foot cable isn't quite long enough to reach the other end of the pipe, re-fray your "bad hair day" end with your needle nose pliers and repeat this from the other end. To get a thorough cleaning may require several passes, each time re-fraying the end of the cable to get maximum scouring. Once you're done, stand the pipe on each end and tap it soundly against the floor (or tap the sides with a hammer) to get the carbon to come out. Mine ejected nearly a half cup of coarse black carbon dust, and when I was finished the entire pipe diameter was clean at both ends and there was zero resistance to air flow through the riser.

I hope this is helpful!

Mon Oct 19, 2020 7:00 pm

Nice write up. I do it pretty much the same, but I cut multiple pieces of cable in lengths about 2-3 inches longer than the last. I start with the shortest piece and work it in both sides until I can't reach any further. Then switch to a slightly longer piece. That way most of the cable is sheaved in the riser, and the cable doesn't flop around and take a bite from my arm or face.

Mon Oct 19, 2020 7:06 pm

I tried this on my 1971 manifold, didn't work. I had to drill holes and then use an extra long drill bit to clean mine out.

Mon Oct 19, 2020 7:35 pm

The cable thing didnt work for me by itself. I ended up heating the heat riser with a propane torch, tapping with a deadblow hammer, repeatedly until some carbon poured out, then did the cable thing again, and so on until I got thru. Took a few hours. I guess some heat risers are worse than others.

Mon Oct 19, 2020 7:42 pm

I was thinking about mine earlier. I need to do top-end gaskets and general cleaning before winter really sets in and this is part of it.

I'll give this a go!

Mon Oct 19, 2020 7:46 pm

virusdoc's method has worked for me on a dual-port manifold. I slid a 5" piece of old 5 mm fuel hose over the cable to grip it with my gloved hand on the free section. The cable spins easily inside it; holding the hose reduces the "whipping" when you first start out and all of the cable is still slack. Reduces wear on the glove leather.

Mon Oct 19, 2020 8:36 pm

I've had pretty good results just from repeatedly bonging the heat riser tubes with a
heavy rubber or plastic hammer. This jars loose the sometimes unbelivable amounts
of rust scale and carbon.

Just as with old rusted galvanized water pipes, cleaning out the rust can result in pinholes.
Those pinholes can develop all by themselves, also. Including into the interior of the
main manifold tube itself. Something to consider if you ever come across a
"vacuum" leak that just cannot be tracked down.

Mon Oct 19, 2020 9:43 pm

When I did this I tried the cable method for a number of days with very limited results. Then I used the long drill bit at each elbow and made enough of a hole all the way through tht I could go back in with the cable and clean out the rest of the schmutz. I got a nice-sized pile of stuff, too.

I patched the elbows with JBWeld and painted the manifold, and all is well.

Tue Oct 20, 2020 8:43 am

When you’ve tried everything else that didn’t work look at this.
https://www.thesamba.com/vw/forum/viewtopic.php?t=666905&highlight=