Another HIF factory .... anomoly

This must be the month to find weird manifolds and SU carbs!

This time is HIF pistons. An HIF piston has about a 1/4" groove through the bottom, from front to back. I would assume that between this groove, and the idle bypass circuit, is the reason an HIF has been reported to flow a bit more air than a like sized HS carb.

In the construction of the SU pistons, there is a steel portion that I assume the alloy was cast around. The steel portion serves as the guide into the piston chamber, the cylinder for the damper and it's oil, and also as the protrusion to the bottom of the piston that the jet needle seats into.

In an HIF piston the biased/spring loaded jet needle has had a variety of the steel keepers that allow the needle to float on the spring pressure. They are always aligned to have the needle biased toward the rear of the piston. Some guides are have a flat side to insure the lock screw has the guide situated correctly, some have a groove, and some only have a line scribed in them to indicate the rearward positioning. In an HIF piston the portion of the previously mentioned steel part, is the housing for the biased needle guide.

I have had 2 sets of HIF's this week where the steel portion was cast differently into each of the 2 pistons. Now, this could be a switched piston issue, but I would have to guess that the design criteria was for the steel portion to be flush with the 1/4" machined grooves in the bottoms of the pistons. Most that I see are flush. Some are equally off, but when like in the attached pics, is enough to alter airflow and to also make it a real question of where to set the depth of the 2 jet needles.

BTW the upward ends of the steel inserts are equally different.

Edit>>>>> well those pics don't show too well. Better pics: http://britcarfun.com/images/HIFPistonAnomoly/

just bought a pair of HIFs on ebay. Pretty sure they will need a freshening. Wonder which version I'll get.

Interesting Jimmy!

The idea of switched pistons seems reasonable to me as the HUGE CHANNEL LOCK teeth marks on one of the bells and the ghost of water contamination on the smaller section of one of the pistons could indicate that the carbs might have been, shall we say, neglected, stuck together and roughly disassembled at some point.

Were there any noticeable differences in the piston-to-bell clearances?

How were the guide tubes different?

Jack

I'm stuck on a set of HIF myself at the moment. The Wiz (Mike Barnes) was kind enough to send me a photo showing how to reference the float to the carb body and then set the float at (.04 +-.02, 1/16" below... whatever). Great if you a flat top on the float to work with... but what do you do with a wedge shaped float? I had the car running (fairly well too) BEFORE I tried adjusting the floats by using the top of the "arc" on the float as the reference point. The car will only run with the choke full so THAT'S too low.

Any ideas... Jimmy???

Cheers,
Newt

Newt,

If you remove the jet and temp compensator, it is much easier to set the float height adjustment with a straight edge. 2 tips while there: be sure that the rivits holding the brass tabs on the floats are tight (they can be tightened up if loose), and also set the tab so it is tight againt the curved portion of the plastic float and the tab set so the float will be above the edge of the body. This way to get your adjustment you are pulling up (as looking at it) on the brass tab to set the float. It gives a more solid end result to the setting.

Pic: http://britcarfun.com/images/HIFfloat.JPG

Jack,

Actually the one piston chamber had been marked with 3 grinder/file marks, as well as one piston.

The pistons/chambers are in average/above average condition, and the plating is still on the steel portions with no signs of having been corroded or stuck.

The steel inserts are solid, and not moveable. I have to assume that they had the alloy cast to them in different heights. The steel insert is the same length on each, and is as short on the top of one as it is long on the bottom.

The discoloration in the lower part of both pistons is definitely due to carbon that had built up on the engine side, which is fairly common to see.

Jimmy, will do but is the float clearance measured from the plane of the carb bottom to the middle of the inside arc on that wedge float? Although I just tried it at the top and THAT didn't work either! On the bright side (sorta) I discovered that the running on valve is broken!

Thanks,
Newt

Newt, To the bottom of the arc. I attached a link to a pic in my previous post.

Also, some needle & seat sets have a spring loaded pin or ball in the top. You have to make sure that this is not compressed when setting the float level. If the spring is a bit weak, the weight of the float can compress it. So to counter that you sometimes have to hold the carb at a bit of a backward angle, as is also shown in the pic.

Sorry Jimmy, I'm new to this link stuff! Unless it's links and there's 18 of them (27 on a good day!).

Oddly enough, the photo in the link is the same one Mike sent me! Good stuff gets passed around no? What confused me was that in your photo the float is laying flat against the square and as you see in my photo (I exaggerated the lift so you could view the entire top of the float in situ) it has a dramatic slope to it and I didn't know if I should set my clearance at the carb or at the jet side. SO! The jet side it is.

Is this a commonly used float in the HIF4?

Thanks again Jimmy... send the check to your work address?

Newt

Actually, looking at it again the bottom of the arc is on the carb side isn't it?

Darn drugs!

Newt

Newt,

Here is another alternate view: http://britcarfun.com/images/HIFfloat1.JPG