PRD Fireball Shop Manual/Correcting Poor Head Seal

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PRD Fireball Shop Manual/Correcting Poor Head Seal

Do not try to reinstall the top when you have any doubt that it is probably not flat, or after having overheated the engine (delicate or extreme). As a substitute, confirm the flatness of the top floor. To take action, you will want a “recognized flat” floor – ideally a floor piece of marble, or a machined steel plate may also work as long as the tolerance is appropriate (as much as 0.001″).

If the top has deposits from the coolant passages, you haven’t any alternative however to evenly sand these down earlier than checking for flatness; use the next process to take away the deposits, do not try to sand them by hand.

Earlier than altering unique dimensions of any half that could be scrutinized, know the relevant dimensional minimums and maximums. For the 2012 PRD 125cc Managed TAG engine, the minimal cylinder top from machined floor to machined floor is 86.80 mm.[1]

To measure cylinder top as described above, place the jug the other way up on a “recognized flat” floor. Take a caliper, and insert the depth measuring implement into one of many bored holes for the top studs (the lengthy studs that run by your entire jug and the top). Fastidiously maintain the gauge as regular to the jug base as doable, and cease when the caliper simply touches your “recognized flat” floor. Your studying is more likely to be a round 87 mm.

Have a flat floor, a fats (chisel tip) Sharpie, and an assortment of wet-sanding paper in 200, 400, 800.

  1. Utilizing a chisel tip Sharpie, mark your entire (flat) floor.
  2. With 800 or larger grit paper laid upright in your flat floor, run water over the floor, over the paper, and place the paper in your floor, guaranteeing all are clear and freed from particles.
  3. Gently sand and the floor on the paper, making use of even power by greedy it centrally. Sand in a round movement for a set variety of revolutions. Repeat the identical variety of revolutions in the wrong way. Rotate the half 180 levels, and repeat the method.
  4. Observe the Sharpie marks. If the marks are fading moderately evenly (with none seen sample), your floor is sort of flat. If the marks are clearly eliminated in a area of the top, however are pretty daring in different areas, your floor is not flat. Comply with the subsequent step in case your floor is not flat. If not one of the Sharpie was left, you sanded too firmly or too lengthy. Attempt once more.
  5. Use at the very least 400, however ideally 200 if you could take away at the very least 0.001″. Utilizing the identical patterned sanding method described above, sand till you’ll be able to observe the cross hatching from the sanding course of throughout your entire floor. Sand extra firmly, however make sure the sandpaper stays flat in opposition to the “recognized flat” floor. You should not want to carry the paper right down to the floor when you have sufficient water concerned; the floor rigidity of the water will hold the paper firmly in place. If the paper is transferring, you may have particles in your floor(s), or your “recognized flat” floor is not very a lot so.
  6. Once you’re happy that the floor is flat, step your sandpaper up one degree i.e. 200 to 400, and sand for lengthy sufficient to easy out the rougher grooves from the coarser paper.
  7. Repeat the method within the earlier step till you have achieved a floor that’s polished to your liking – you’ll be able to actually do that perpetually, so do not go overboard except you are extra serious about sanding then racing. 🙂

Word: This process is an alternative choice to machining or “skimming” to realize a flat floor. Not solely is that this process simpler and requires no equipment, however additionally it is unlawful (typically) to machine your head. Utilizing a mill or lathe in an effort to take away as little materials as doable possible requires added tooling and time consuming fixturing effort; sanding removes solely the fabric required to get a working seal of the top.

Tremendous shut up of a superbly flattened jug.


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