Slide Valve
Engine Installation

by Eric Perez

How do we get a Novarossi Slide valve engine installed on the Traxxas Nitro-4-TEC or HPI RS4? The modifications shown here will let you successfully get more ponies into your ride. Note: This won't make your car any easier to drive. If you have any weak drive train components or a questionable belt it will show itself in the first couple of runs with this beast of an engine. Make sure your rear belt is not loose, or you'll break it in a hurry. We want the rear belt snug, not tight. The rest of the car seemed to stand up well to the increased power.

Note: on HPI cars you may need to bend the carburetor linkage slightly to get a smoother operation.

Okay, now that you've seen the pictures lets explain what to do. First follow the instructions from the traxxas/HPI web site on how to install the Novarossi engine on the chassis. To summarize things a bit:

Note: the following is a summary of how to convert the long-shaft Novarossi to short-shaft. The Nitro 4-TEC uses a short crankshaft engine. HPI touring cars use std length (also called std. airplane length) crankshafts.

1. Install clutch on engine and determine the excess amount of crank shaft that you need to cut to attach the clutch nut snug with the fly-wheel.
2. Remove 5 mm grub screw from engine crank-shaft and cut the screw slightly longer than your measured dimension. Note: do not cut the front of the 5 mm grub screw this is where the 2.5 mm hex wrench goes. Always remove the grub screw and cut the back portion of it. Remember you need the hex side intact so you can re-install the screw back on the crank-shaft.
3. Install grub screw on engine and clutch bell assembly. Tighten clutch nut. If it's snug, good job. If it's loose, cut or grind a little more material from the grub screw and assemble the clutch again. Repeat until the clutch nut is tight. Don't forget to use loctite on the grub screw once you have it the correct length.

Steps 4-8 for Traxxas Nitro 4-TEC only.

4. Take engine mount and cut the center section out. You can use a hack saw, band saw, precision saw  or dremel. Clean the cut with a file or sand paper.
5. connect engine to the (2) piece engine mount. Use lock tite on 3 mm screws.
6. Install header on engine. Use loctite on 3 mm screws.
7. Install clutch bell assembly (just like before). use Loctite on 3 mm screws.

This finishes the engine portion of the instructions.

Now for the not so obvious steps.

8. For the slide to work properly you need to grind off a small groove on the upper fuel tank rail. This is the plastic part that surrounds the fuel tank. The slide valve will interfere with the lip just under the slider. Remove a little plastic at a time from the fuel tank rail, until the slider will go over the lip without making contact with it. Note: You will be close to the tank, if your dremel or exacto blade slips you could damage the fuel tank. Work slowly and don't over do it on the cutting job.

The remaining steps are for both Traxxas and HPI touring cars.

9. Assembling the slide linkage:
    To get this section going you are going to need the following parts:

  • (1) Kimborough RC10 GT servo horn or Traxxas servo horn for your servo. Can be substituted for equivalent.
  • (2) linkage rod guides from Traxxas. These are the parts that screw to the servo horn and the linkage rods slide inside of them. Your current throttle linkage has (2) of these. Traxxas part No. 3180
  • (2) 2-56 push rods that have 1 inch of thread at the end.
  • (1) 2-56 small ball cup. Typical brands are Dubro, Sullivan and great planes. This is the part that snaps on the metal ball on the throttle slider.
  • (1) plastic 2-56 nut. This is to fine tune the brake action.
  • (3) plated wheel collars 2-56.
  • (1) small spring. You can use the spring that's in the barrel carburetor linkage in your kit. Check the Traxxas site for Part no.
  • (1) small piece of silicone fuel tubing.
Cut the servo horns so that they resemble Mr. T "I pity the fool". Drill out holes on the servo horn to fit the rod guides. Make sure the holes are large enough so the guides can rotate freely. Note: Exact length based on the N-4-T for HPI cars cut linkages 1/2" longer and trim to fit. Cut one of the push rods so that it has 1/2" of threads showing and is 2 1/4 " long. Attach the ball end and the collar, then the spring. Slide it into the guide and secure with another collar. Now cut the remaining rod so that it has 1" of threads showing and is 5 5/8 " long. Thread the plastic nut into the rod and slide a piece of fuel tubing. Remove the brake cam wire from the shaft and insert it behind the fuel tubing. Now insert the rod end into the remaining guide and slide a collar at the other end of the slider. see picture.

10. Remove the throttle servo from the chassis rotate it 180 degrees and re-install.

11. Attach the linkage to the carburetor and the cam lever on the brake shaft. test radio for proper throttle and break function. Re-adjust linkages as necessary, use pictures as a guide.

hope this helped. As stated earlier you may need to re-tune your chassis because the car will handle different. I suggest increasing shock oil wt by 10 to tame chassis roll down a bit. If your previous engine was a slouch you may also need to re-calibrate your trigger finger :)

Whoop some R/C Butt!!!

Eric Perez, 1998, 2011
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This page last modified: 07/26/11