Bongo Fury

Steve, you have a couple of emails.

Doone wrote:Steve, you have a couple of emails.

Thanks Al and Lorna - Had a good look at your diagrams and decided where the knife is going in (More likely to be a laser cutter now I have seen the pics).
Gotta say the head construction aint what I imagined. Not having EVER seen one in real life, I had conjoured up a picture in my mind, and how wrong I was
Surgery should be fun ........and of course informative

You may think I know nowt about cylinder heads, and you would be correct. This is the very first one I have seen.
This cylinder head to be dissected was donated by a well respected member of the forum.

On initial viewing, there is a definite crack in the head at cylinder No.3 between inlet and exhaust port (as marked on pic.)
Also, I observed sooty deposits on the inlet port at the crack (also marked on pic), which suggests that exhaust gasses have been escaping into the inlet port.
Any light thrown on this would be gratefully received, ideally prior to cutting. Any more ideas where I should cut?
When I put the head to the knife (laser probably) I am hoping it may show the extent of the depth of this crack.

How many cuts can you make ? Would it be worth slicing it in the horizontal plane several times say every 1cm that would expose all the cooling paths that the water takes perhaps - like you I have never even seen a head in the loose state so not sure what might be found !

g8dhe wrote:How many cuts can you make ? Would it be worth slicing it in the horizontal plane several times say every 1cm that would expose all the cooling paths that the water takes perhaps - like you I have never even seen a head in the loose state so not sure what might be found !

Hi Geoff
The original reason for wanting to look inside the head is to find the highest point at which air could get trapped during bleeding. Visually, this point appears to be at the sensor point above the coolant outlet on the drivers side/front of engine (needs confirming by cutting). Before Bongonads turned gangster, he did mention this as a point to release trapped air. Kirsty has already tried this and suffered scalding coolant for her troubles.
Number of cuts depends on machine used. I have the following at my disposal:
Laser cutter - Ideal because there are several different types of material in the head (aluminium, hardened steel valve guides and valve seats, etc) but I need to check the full depth to which I can cut. This machine can cut 50mm thick stainless steel, but the head is thicker. Maybe when cutting aluminium, a greater depth can be achieved. Also, I'm not sure what the surface finish will be like.
Milling machine - This will give a better surface finish, but metal is removed, hence the reason for being cautious about WHERE i make the cuts.
Band saw - Throat of saw limited - will only be able to get cuts across th head. Also, the saw may not be happy cutting through the harder materials (valve guides etc)

I have to admit to not reading all the stuff in this wonderful thread but found an interesting quote about the system the Bongo uses where the thermostat is in the return side of the radiator.........designed to keep the cylinder head temperature more stable and reduce the risk of cracking the head. It is being used more often in modern engines to reduce emissions.

Engines which require a tighter control of temperature, as they are sensitive to "Thermal shock" caused by surges of coolant, may use a "constant inlet temperature" system. In this arrangement the inlet cooling to the engine is controlled by double-valve thermostat which mixes a re-circulating sensing flow with the radiator cooling flow. These employ a single capsule, but have two valve discs. Thus a very compact, and simple but effective, control function is achieved.

This system uses the same 'stat that the Bongo and many others use

dandywarhol wrote:I have to admit to not reading all the stuff in this wonderful thread but found an interesting quote about the system the Bongo uses where the thermostat is in the return side of the radiator.........designed to keep the cylinder head temperature more stable and reduce the risk of cracking the head. It is being used more often in modern engines to reduce emissions.

Engines which require a tighter control of temperature, as they are sensitive to "Thermal shock" caused by surges of coolant, may use a "constant inlet temperature" system. In this arrangement the inlet cooling to the engine is controlled by double-valve thermostat which mixes a re-circulating sensing flow with the radiator cooling flow. These employ a single capsule, but have two valve discs. Thus a very compact, and simple but effective, control function is achieved.

This system uses the same 'stat that the Bongo and many others use

For those insomniacs who wish to see the Original Design patent
then feel free to read. As Dandy says, this kind of cooling system, designed and patented by Toyota engineers in 1992 is now more commonplace as Dandy says to reduce emissions due to faster warm ups, which indeed was part of the design brief

Ye cannae beat a Toyota HIACE eh? ...................although I remember seing the 'stat on the return side on a 1980s VW Passat

Although the Toyota Regius has some 60 pipes in the coolant flow and return system And we thought the bongo was bad!!!

Hi
Being a North of the Border man, I'm sure you're used to all these pipes...the Great Highland Pipes have only 3 drones and a chanter...imagine trying to get music from a Bongo
EEeeee...ya' jus have to love pipe music!!!!!
Cheers
Helen

The stat used in a Bongo, as Alan suggests, does indeed control the inlet temperature quite precisely due to its configuration.
The stat travel/coolant volume isn't proportional over its full stroke.
Of the 5mm total travel, the first 1.5mm has a restricted flow, initially allowing a very small amount of potentially cold coolant to enter the system.
The remaining 3.5mm increases the flow proportionaly as the temperature increases further.

A truly clever piece of kit.

A truly clever piece of kit.

Who was it who thought the Bongo was just a house brick on wheels... never judge a book by its cover.

Doone wrote:

A truly clever piece of kit.

Who was it who thought the Bongo was just a house brick on wheels... never judge a book by its cover.

Aye, Mazda are clever copiers................

g8dhe wrote:How many cuts can you make ? Would it be worth slicing it in the horizontal plane several times say every 1cm that would expose all the cooling paths that the water takes perhaps - like you I have never even seen a head in the loose state so not sure what might be found !

Spot on IMHO, localised boiling will be less controlled where it is needed most with the stat on the inlet (yes I know I bang on about it but it matters). There maybe a difference in colour of the exposed waterways close to the exhaust valve where boiling has taken place.
'Cooling paths' are difficult to understand as size alters speed this then alters pressure and then alters the boiling point.

Sorry about this (changing animations) but I thought it may simplify understanding of the circuits.

First of all, the heater circuit. This is constantly flowing when the engine is running. This diagram is to show the heater circuit ONLY and does not represent a condition that will ever be experienced - just the heater circuits.



This diagram shows the circuits flowing during the warm-up cycle - ie up to the point where the themostat begins to open - ie no flow from the radiator bottom hose to thermostat.



This diagram shows the circuits flowing during normal running conditions where the thermostat is positioned somewhere (anywhere) between its fully closed and fully open states.
Variable flow from both the radiator bottom hose and cylinder head to the thermostat now occurs.
The rate of flow from radiator and cylinder head depends entirely on the position of the thermostat.



This diagram shows the circuits flowing when the engine is producing enough heat to fully open the thermostat and extra cooling is required. Towing, either steep or long inclines, stationary vehicle (stuck in traffic with no radiator cooling from forward motion). This is where the fans are most likely to kick in.
Notice that the bypass circuit from the cylinder head has been cut off by the stat.


Please feel free to point out errors. I am really tring to get this absolutely correct.