music box

Thursday, March 26, 2009

Skimming The Cylinder Head

As per your advice before, true to your prediction, engine oil leaks from between the cylinder head and its gasket reappeared because nothing was done to rectify the cylinder head except changing its gasket twice. This time, the cylinder head was suspected to be faulty and the mechanic proposed that it be skimmed.

I am very wary of such a procedure and mindful of your earlier views about it because i would not want to suffer another round of workshop blues posed by different sets of problems. To use laymen, skimming seems a complicated and delicate process. What problems would arise if a hastily or not properly done skimmed head is fitted to the engine?

There are two ways to take material off the cylinder head:

1. If there is very slight uneveness, using valve grinding paste and a large flat glass, one cap lap the head until it is flat. This method takes off a very small amount of material and is usually not a problemat all.

2. The second method involves using either a shaping or milling machine to take off material from the surface of the head and this is done when there is a quite large amount of material that needs to be removed.

This procedure require quite a high degree of skill on the part of the machinist as he must know how to clamp the head in an absolutely level position in realation to the cutter and he must also know the limit of how much material can be removed.

Every cylinder head has a limit to how much can be removed because if too much is removed, the following can happen:
a) The compression ratio may get too high and you will get serve detonation resulting in piston failure.
b) The valves may hit the piston.
c) You may break into a water passage or the material may get too thin and when the head is torqued down, it may crack.
d) You may have difficulty keeping tension for the camshaft.

So my advice is to make sure that the guy doing the job knows that he is doing or else take the job to the franchisee holder who will have the right information as to what can and cannot be done.

Fuse For Horn

I wrote recently about changing my car horn which unfortunately went unanswered. However from your reply on ther column, I assume that it is possible to do so, provided the specs confirm with the electrical ratings and the installation is wired properly.

According to the fuse chart (interior fuse block) in the Owner's Manual the fuse for the horn is rated 10A. A specific fuse for horn relay is not indicated, although there is a main relay indicated in another fuse chart (engine room).

However, a fuse rating is not stated. Does this mean that there is no dedicated relay for the horn at present? I am seriuosly considering changing the feeble-sounding original horn on my Chevrolet aveo lux to something more "robust-sounding".

Please advise on the type of horn and suitable specs to comply with when replacing the existing horn, particularly on whether a dedicated relay is required and its rating.

The 10A rating for the fuse is all that you need. Most horns have relays already and you need to check if the relay has sufficient capcity for the new horn, or else you need to replace it with one with a higher capacity. Usually the suppliers of the higher capacity horns also supply a relay in the box. Check the wiring diagram in your Owner's Manual and it should tell you the location of the relay.

ABS System

I bought a new Honda Stream 2.0 i-Vtec year 2005. When I brake at low speed, it was OK but at high speed, 160km/h and above, there was steering vibration. Still under warranty, I sent my car to the Honda workshop. The disc was lathed three times but the problem still persisted.

Finally Honda changed the disc with a new one. The same problem occured. Then I changed the rear brake pads but there is no solution in sight. It is normal for the ABS system?

If the brake discs have been changed and there is no run-out on the disc, then obviously one needs to look at the wheel hubs if they are running true. Even if the car is now out of warranty, and the problem was brought to the attention of the franchisee holders during the warranty period, they are obliged to fix the problem at no cost to you.

I suggest that you make an appoinment to meet the head of the after sales division and have a chat with him about your problem.

Idling Poser

I have a 2000 Proton Waja MT which was running fine until recently when idling speed of the engine came down to less than 500 rpm after the engine had warn up. Normally it's around 750rpm. What is wrong with this car?

Have you send the car in to be checked? It could be faulty idle valve or even misfiring plug. The best is to let the people with the right test equipment check it out.