18 replies to this topic

[John Clayton]

Back in mid 09 I had a persistent overheating problem with my Mini which turned out to be a Cyl Head Gasket failure.
The head came off, re cut valve seats & built it back up with head skim (To Re-dress the valve seats. De-coke the head + re-cut the seats + a 2thou skim cost me £65).
It had a Copper AF460 gasket fitted http://www.minisport...info_AF460.html and has done the following events since then:
Track day
Autosolo
4x Rally Sprints
2x Woodbridge rally sprint
[diligently cleaned cooling system/Rad using a hose and Holts Rad Flush (2-step) http://www.halfords....tegoryId_165750 The water was running clear by the time I had finished, but I did spot a few flakes of rust lodged in the matrix of the car's brass 4-Core Rad subsequently, which was irritating. I refilled it with fresh Comma Red OAT antifreeze -which I confirmed was definitely OK for classic Minis -and distilled water).
A few hours of road driving (mainly on 1 day a couple of weeks before the Track Day)
Track day


The temp has been normal on all events, but they are often 'short bursts' i.e. 3-8 minute stages, typically. At Woodbridge we noticed that the Temp would be 25% above 'N' at the end of each stage but we drove around for a few minutes to get some airflow through the Radiator (Rad) before returning to the paddock each time and no problems resulted.

However, on the final event in the list above I noticed in the morning that the temp gauge (which has a scale of ' C N H') was halfway between N and H (and there was a light spray of coolant droplets on the passenger side of the windscreen) so I came off the track.

We continued to closely monitor the coolant level during the day and on each track session it would get hotter than 'N' and then spray a bit of coolant onto the windscreen after 5-7 laps. Looking at the water marks on the rad, I think it might have been bubbling out of the radiator cap and dripping onto the fan, which fits with the spray pattern I saw inside the engine bay. However, I don't know why the coolant wasn't going out down the overflow pipe in the radiator filler neck (I checked the pipe wasn't blocked).

The engine also sounded a bit rough and this got worse throughout the day. There is evidence of a small coolant leak out of the cyl head gasket on the front of the engine block (white/pinky staining from my Red AntiFreeze which got more obvious during the day).

We have done a Compression test and it was about 150psi in all 4 cylinders which I understand is well down? Back in 09, the cyl hd gasket failure was detected by cylinders 2&3 producing about the same psi (and the good cylinders were about 175psi).

• Anyone got any ideas as to why the Cyl Hd Gasket isn't lasting that long?
• The Minisport link to the gasket quotes it as for '1275/1400 engines' -my block is 1293cc so would this be causing a problem?
• Are the Head Studs 'stretch bolts' i.e. should I have replaced them when the Hd was off last time?
• I have just checked the Head bolt torque and they were all spot on 40lb/ft (as specified in the manual) apart from the one that is on the front right of the engine from the Driver's perspective (this needed approx 1 extra turn to make 40lb/ft). My mate was saying that I need to re-check the head bolt Tq every couple of outings on a rally engine (although this is a pain when it means having to glue a new Rocker Cover gasket on each time)
• Perhaps my problem is that the BLOCK is warped (rather than the head)? [I hope not because that is presumably an 'engine out' job to skim the block?
• Is there any head gasket cement that will help (especially if the car does have a warped block)? e.g. http://www.audioworl...hp?topic=2936.0
• Do I need to get Competition Head Studs? The ARP ones are hugely expensive! http://www.minisport..._and_Studs.html
• My intention is to try fitting the BK450 Metro Turbo Gasket (and buy the whole BK450 Gasket set) http://www.minisport...40BK#aGEG1140BK

If it fails again, then the only other option I have is this one:
HEAD GASKET COMPETITION 1300 AND 8 PORT
http://www.minispare...=...5695&title=

However, the other question is:
"Did the engine get too hot and then blow the gasket" OR "Did the gasket blow and cause the coolant to get hot"
Could the water pump have been turning so fast at the high revs involved (4000-6000rpm continuously) that the coolant was cavitating (and so the pump would need to be slowed down via a larger pulley wheel)

I intend to buy and fit this Oil Cooler:
http://cgi.ebay.co.u...=item20b78f10ce

and I could always try getting better cooling on the engine e.g.
Remove Rad and soak it in Bilt Hamber DEOX-C overnight to dissolve any rust inside: http://www.bilthambe.....osion Removal

If the car's still getting too hot, I could try Redline Water Wetter http://www.redlineoi...ts.aspx?pcid=10

or a new Aluminium Rad (or even a front-mounted Metro Rad but this sounds like a lot of work to make it fit).

The possibilities are endless! Any advice on how to sort out this problem would be much appreciated...


FYI, the car’s full spec is listed on the its blog:
http://www.theminifo...howtopic=129848

Edited by John Clayton, 24 May 2011 - 06:26 PM.

[Broomer]

I have found you you need to pay alot of attention to the retorquing of the head bolts after re fitting the head. i do this 4 or 5 times after the engine goes through a couple of heat cycles.

[bmcecosse]

First step - have you tried a new high pressure rad cap? Then - what thermostat is in the head ? If the car is pretty much just for competition use - a blanking sleeve in stead of a stat will help to keep peak temps down. Alos eliminate the bypass connections. Do you still have a heater connected? This helps to move water from the dead end of the head. I also found the smaller diameter water pump pulley from earlier A series engines works well. Your compressions are v poor for a competition engine - should be ~ 200 psi. The gasket hasn't blown - it may be weeping some water. And as above - did you retorque it after the first heat cycle ? The standard studs are fine IF they have the 'y' mark on the top. Using the shouldered nuts and oiled threads - torque in stages to 50 ft lbf. Certainly don't use any form of cement - and the turbo gasket should not be necessary.

[John Clayton]

I haven't tried a new Rad Cap yet -by "high pressure rad cap", do you mean a '15 psi' cap?

My existing one says 15psi on it, but I will get a new one in case the current one is faulty:
http://www.minisport...RC1110#aGRC1110
Radiator Cap - 15lb - No Sender, 1980-92


The car has a Thermostat Blanking Plate fitted.
I will check to see if the bypass connections have been eliminated -if not I take it this needs to be done?
I believe that the heater was disconnected long ago.
I didn't retorque the Head Bolts after the first heat cycle, but the mechanic who did the work on it may have done?
I will look to see if the Studs have the 'y' mark on the top
What are 'shouldered nuts' and where do you get them from?

[bmcecosse]

The A+ engines use head nuts with a washer (my 'shoulder') included. The nuts must be retorqued after the first heat cycle - and the valve gaps reset. But your compressions are very low - indicating a general engine overhaul is on the cards anyway ..... The bypass elimination is not 'essential' but worth doing if the head is off anyway. Either connect the heater - or at least the little rad out of a heater and mount it behind the grille - to help dissipate as much heat as possible.

[Sprocket]

Nothing wrong with 150psi comporession figures, it all depends on the overlap and duration of the cam. Air and engine temperature play a large part also. We have had this discussion before

Are you sure this is a head gasket issue other than an engine tune or cooling system issue?

Have the coolant in the rad tested to see if it contains any combustion products.

And if you are looking for an ultimate head gasket, try the laminated steel Cometic gasket

Edited by Sprocket, 25 May 2011 - 09:37 AM.

[John Clayton]

Here's some gen on the Cometic Gasket (and how to fit it -see bottom of 1st weblink):
http://www.rpmmachin...tin-acura.shtml

http://www.burtonpow.../c4146-051.html

http://www.sbdev.co..../2L_Gaskets.htm

http://www.importper...ticgaskets.html

[John Clayton]

I received the following info from the Mini motorsport expert Peter Valentine, which is worth passing on FYI:

Hi John,

What fan ae you using. You need the 6-blade 'Export' fan for a rally car and it is absolutely vital that the fan sits centrally in the shroud as it is, effectively, a 'ducted fan' and the tip to shroud clearance must be as swmall as possible. On my 'S', which is 1310 cc, I also use an electric fan the other side of the inner wing with a shroud between the rad and the inside of the inner wing (as a Mk.1 & 2 had as standard). Mine is manually switched from a permanent live (i.e. not via ignition) and can be left on when ign is switched off to give rapid cooling.
Get a capilliary-type temp gauge which reads accurately in degs C. Those electric ones are useless.
You should have a thermostat blanking sleeve rather than a thermostat.
I doubt that you have a distorted block deck. That would be very unusual. The only time I've ever seen a block deck damaged was after a car had been run with a blown gasket and the water eroded the block deck locally.
Use only a BK450 'black' gasket. Fit it dry with no oil on either the gasket , block or head faces.
For a competition car always use the ARP head studs. They are not 'stretch' studs, and you should use 50 lb.ft torque, getting there in 3 stages, 30 lb. ft., 40 lb. ft., then finally 50, making sure you use the correct sequence when tightening.
The compressions are definately down. Whilst the head is off, why not measure and re-calculate the C.R., re-lap the valves and check everything out. Don't forget, when checking the actual compressions, you must have all the plugs out, the throttle fully open, some light oil down the bores and a fully charged battery.
I've always believed that a 'fancy' radiator is unnecessary, but a good standard one in top condition, with the heater fitted and with the heater valve always open to keep the heater matrix 'in circuit'.
The only time I've had an overheating 'S' was on a Belgian Int. Historic Rally when the outside air temp was 102 deg F. We had to run with the heater fan on, plus the 6-blade and the electric fan, then it was OK, but we lost a lot of personal weight and had to drink literally litres of salted water! (but 7th overall and 1st in class was OK).
I doubt that you have any serious problem, rather that it's a build-up of small issues in the cooling system. A 1275 in rally trim can be a bit temp-critical and it doesn't take much to push it over the edge heat-wise.
The only other issue is fan pulley size. Too big and the fan runs too slowly, too small and the fan can go so fast that you nget what bis known as 'cascade effect' or 'discing'. That is where the blades are going so fast that no air flows as the fan acts like a solid disc. The original 16-blade fans used to this and 11-blade plastic ones can at very high revs.
I hope all this helps. Let me know how it goes,

All the very best,

Peter

Edited by John Clayton, 25 May 2011 - 04:12 PM.

[Ethel]

A series blocks, even heads, aren't easy to distort being all cast iron. They can suffer from erosion though, if the gasket has been blowing for a while. I'm not suggesting that's the case here. The head studs shouldn't get anywhere near yield, but it's worth thinking about if they have an unknown history.

As Sprocket said, I'd try and establish that the gasket really is blowing before ripping it to bits, analyse the coolant and/or do a leak down test.

[John Clayton]

Here are some decent Head Bolts for motorsport use:

HEAD STUD & NUT SET(STUDS IN EN24 NICKEL CHROME MOLY STEEL) C-AHT280
http://www.minispare...=...4310&title=
GBP 57 inc

http://www.minisport..._and_Studs.html
MiniSpares only uprated bolts appear to be ARP sets which are
a) Very expensive (GBP157inc)
b) Include the rocker bolts (which I don't think I need -unless anyone disagrees?)

[John Clayton]

I believe that I have 2x 2blade metal fans doubled up at present.

It sounds like the 6-blade fan (GBP 30 inc) is what I need:
http://www.minisport.../Mini_Fans.html

although interestingly, Minispares reckon that my existing set up is likely to be slightly better for cooling:
http://www.minispare...=...3081&title=

A lot of the events are relatively slow speed i.e. 15-35mph, with regular bursts up to 60mph, so not sure at what speed the fan's airflow is overtaken by the airflow resulting from the air pressure in the engine bay (from the grille intake)?

Edited by John Clayton, 25 May 2011 - 04:32 PM.

[John Clayton]

This 'variable pitch fan' is an interesting idea, but if the design was any good I'd have thought that it would still be available nowadays (but it's not listed by Minisport or Minispares):
http://cgi.ebay.co.u...=item4159f79094

[John Clayton]

A very good article on avoiding Head Gasket failures here (including which torque settings are best):
http://www.minimania...27/ArticleV.cfm

[John Clayton]

The only other issue is fan pulley size. Too big and the fan runs too slowly, too small and the fan can go so fast that you nget what bis known as 'cascade effect' or 'discing'. That is where the blades are going so fast that no air flows as the fan acts like a solid disc. The original 16-blade fans used to this and 11-blade plastic ones can at very high revs.

I found the above quite intriguing so got my 'aeronautical' head on to ponder further these questions:
Q1) Could the blades stall if the RPM was too high?
A1) I don't believe so as the higher the rpm, the greater the slipstream through the fan so the less the angle of attack. To put it another way, while 'coarse pitch' blades may be stalled when they initially start to turn (i.e. as the engine starts up), as they start pulling a slipstream through the angle of attack will reduce and they will return to laminar flow

Q2) What is the max speed of a propellor?
A2) Whilst the tips of a prop CAN go supersonic, "To produce maximum thrust at full power your tip speed should fall between .88 and .92 mach" (mach being the speed of sound). If a Mini fan is 12" in diameter and doing 6500rpm at 60deg Fahrenheit (15 deg C) then the tip speed is 232 mph which is 0.305 mach. An extreme example of a 14" fan in 105 deg F (45 deg C) doing 7500 rpm is still only 0.393 Mach. Therefore, the fan can rotate a lot faster before its airflow peaks and then reduces (although a Mini fan is not a well honed blade like a propellor and the airflow into the fan will be messy/partially obstructed by the engine being in the way, an apparent slipstream from 90 degrees i.e. the radiator is side on to the ram air effect through the grille etc.). http://www.pponk.com...S/propcalc.html

Q3) Could something similar to 'cavitation' occur?
A3) No -this appears to be purely something that only occurs in water (much denser/slower flowing than air) with a marine propeller screw http://en.wikipedia.org/wiki/Propeller

So how many BHP could be lost by a mechanical fan compared to an electric one (assuming the electric one is 'off')?

A 358.6HP engine lost between 19 and 40 hp (depending upon which fan was fitted) so a power loss of 5.3% to 11.1%:
http://www.carnut.co...mblin/dyno.html

In another test it was approx 6%:
http://www.carcraft....loss/index.html

Kenlowe reckon it is typically 8.5%:
http://www.kenlowe.c...fans03.html#no3
and they also say that "the energy absorbed by the fan goes up by the cube of the speed" which is significant for motorsport users as our fans' blades still have to be coarse enough to cool adequately at low rpm, but they will also then be revved far faster than the normal rpm range for a road car (i.e. the blade pitch will be WAY too coarse at normal rally rpm of 4000-6000 continuously)

Interestingly, Kenlowe also say in the article above that Fans with a Viscous clutch waste nearly as much power as a belt-driven fan, (but their stats may be marketing exaggeration).


However, when an Electric fan is running it will be using up some HP due to the extra load on the alternator and on a Mini with a side-facing radiator, I expect that Electric fans are on much of the time (certainly for motorsport/track use as is being discussed in this thread).

Will an Elec Fan also lose much horsepower?

A 60 amp alternator eats approx 1.46 hp according to someone on this forum:
http://speedtalk.com...php?f=1&t=22191
and this author reckons that a 100% efficient 55 amp alternator (something that will never occur in reality) will draw 1Hp, so there is broad agreement.

Therefore, for a typical electric fan drawing just 7.2A
http://www.minisport...fo_PACCF55.html
therefore this fan would draw only an extra 12% of the alternator's capacity (1.46hp + 12% load = 1.75 hp). Thus, an electric fan's load is likely to be only about 0.3 hp upon the engine -not much to worry about!

So if my 100Bhp engine went from a mechanical to an electric fan it could theoretically save about 5-11 Bhp at the wheels; quite a lot.

Edited by John Clayton, 25 May 2011 - 09:02 PM.

[John Clayton]

The post by chairchild » Fri 14th Jan 2005, 12:15am in this thread:
http://www.minifinit...i...30&p=145208
estimates that:
"If your engine's at about 6000 rpm, you'll save about 2Bhp by having an electric fan, and about 4Bhp by having an electric water pump. I'm also going to be fitting an electric oil pump - just to make sure"

I wonder how much power the Dowty Aerofan (variable pitch fan mentioned earlier in the thread) saves? I'm surprised that David Vizard, Clive Trickey or similar haven't had it on a rolling road to see...