Re: The Wonderbus will NOT die!

Well, yeah that's one way to decrease the volume of the combustion chamber and lower CR. But I'd like to keep the "squish" area nice and thin, to get a more complete burn. As I understand it, the flat areas in the combustion chamber, above and below the opened up area where the valves and plug live, perform a useful function. As the piston comes up during the compression cycle, the piston gets real close to the head in those flat areas. The mixture squirts out and creates turbulence in the larger combustion area. This lowers the octane requirement of the fuel, good for a bus. As I understand it, the mixture needs to burn quickly and with a smooth progression from the plug to the outer edges of the chamber. If the flame's path is roundabout, some areas might detonate before the flame reaches it. A lumpy, unorderly mess. Like oatmeal with firecrackers mixed in. A short flame path and a lot of turbulence creates good, fast, smooth combustion -- reducing detonation.

From what I read, there is more than one way to achieve the desired turbulence. "High-swirl" stuff, like intake swirl as well as combustion chamber "squish." I don't think the VW engine uses intake swirl (as far as I have been able to determine) so I want to make sure that my bus's engine has plenty of squish.

I may have some of this wrong -- I'm just a student here.

You should also remove any sharp edges from the combustion chamber cause the carbon deposited on them glows red when the engine is hot and promotes detonation. Suspect areas are the edge between the flat and the concave area of the chamber, the valve edges from the chamber side which should be carefully rounded, and the spark plug ends (check that the spark plug round face doesn't protrude in the chamber). If the spark plugs protrude into the chamber, you can either fit 1 (only) copper washer between head and spark washer (making sure there is a good seal), or round a bit the sharp edges around the spark end every time you replace the plugs. If the spark is so long that threads are exposed in the chamber, you have to use a different type of plug.

You should not use a dremel or a file to round the sharp edges, just some wet or dry paper. A radius of about 0,5mm is enough for the purpose.

Bill, '67 bug.

This goes on the plug before installing? And we hope it does not fall off when the plug is removed for whatever reason and disappear down into the tinwork with a merry tinkling sound.

I'm not getting "round a bit the sharp edges around the spark end every time you replace the plugs." This is something that is done to the plug? Round off the end of the threaded portion so it's smooth like a baby's bottom?

Sorry for the slowness this morning. Brain is in neutral.

If you can find a washer which is a tight fit on the plug you won't have this problem. Anyway, if the washer falls from the plug, you can retrieve it with your finger. It wont fit in the cooling holes of the head, so it wont go too deep. Anyway, the idea here is to try the plugs with the heads removed to check that the plug's face is flush with the combustion chamber, and not leave it to chance. If it isn't flush, first try to find another spark make or different spark type that will fit. If you cannot find any plug that fits properlly, then use the washer to compensate the extra length.

Another preparation step for the new heads I forgot to mention before, is to check that the cooling air paths through the fins are unobstracted. Usually, to the sides of the fins there are casting marks that obstract air flow that have to be removed with a saw or other tool of your choice. Also the holes that go from top to bottom of the head near the exhaust ports, exhaust valve guides and bellow the spark plugs, are clogged with excess metal from the casting process. You have to unobstract these holes to permit the head cool properlly.

Bill, '67 Bug.

How is it that you are so wise in the ways of spark plugs?

Thanks for the advice on that. I'll be certain to set it up properly before cc-ing the heads.

Roger that. I have read about this step elsewhere and note that the tool of choice to remove the excess metal is called a "riffler file." If you got to

It's a step I failed to follow in the past until I read about it in a book. Then I was surprised to find out that in many cases the commonly used spark plugs would fit deeper than they should in the combustion chamber. With 50+ year old technology as the VW engine, there is VERY much experience and so much material to read about, either on books or on the internet. Whatever problem you have, someone else has come across it in the past and written something about it. That's a very wide knowledge base you will not find for many other cars (if any).

Bill, '67 Bug.

Ah books -- is there anything they don't know?

Pursuant to that, I am searching the 'net for a canonical list of spark plug types that can be used in the 1600 head, along with their dimensions so I won't have to ask the lad at Pep Boys to open all the boxes for me until I find the right size. I must not be Googling the right terms, 'cause I got nothing.

There is a Technical Data online source for spark plugs here:

This is not something you should lose your sleep about, especially since you use unmodiffied stock heads, just check the plugs on the heads before installing them to see if something is wrong.

Bill, '67 Bug.

Thanks, Bill!