1949 Dennis F1 Fire Truck Restoration

Hi Bugly, if you are tapping a thread into cast iron you should make it UNC. If the threads go into the water you can coat them with a sealer used on holden head bolts.I can't remember what the stuffs called but it works well.

Its called Holden Head Stud Sealer (or something similar), you can buy it from Holden spare parts (they will know what you are asking for). About $70 for a small 200 ml can, but it does work well. (Buying small quantities of aviation sealant will probably cost an equivalent amount anyway)

Bugly - Fine thread bolts have inherently more strength, in the direction of tension, because they aren't cut as deep into the bolt shank as coarse threads.

However, in practical terms, coarse threads are superior, because they are quicker to do up and undo .. and coarse threads are less inclined to "pick up" (i.e. - gall).
Coarse threads have a better ability to handle trash/corrosion in the thread, without damage.

Cat settled on coarse thread bolts (UNC) as virtually standard hardware, way back in the early 1930's (with a few odd exceptions) .. because essentially, fine threads are a right PIA .. with slowness in doing up and undoing, a major hassle .. and with regular thread destruction a common problem, where corrosion, dirt, dust, mud, and other nasties, are regularly thrown up, or build up, around the thread.

10mm is adequate thickness to retain a 5/16" bolt .. after all, it's 2 mm wider than the bolt shank diameter. My vote goes to UNC fasteners.
Also, another thing to remember, is that SS fasteners are not HT .. they are grade 2 or 3 at best, so go easy on the tightening torque on SS bolts.

Bugly, go UNC, Loctite make a hydraulic thread sealent which will work perfectly. I can't tell you the number because I'm at home, but I would imagine a small tube of this stuff would be about $20, you could even just use Loctite Master Gasket, it won't be a high pressure system.

Thanks guys, I really appreciate the comments! So far its 3 out of 3 suggesting UNC, so on the strength of the greater knowledge and experience of you all I will tap with coarse threads. I guess the original BSF threads have well demonstrated that fine threads when rusted or contaminated are a right PIA. If a coarse thread helps the bolts undo in the future, then its a good thing!

Bigcam, you're right ... The Dennis engine is not a high pressure system. In fact it is unpressurised, and relies on the water volume and the large radiator for cooling. Another good reason to fit a temperature gauge! And I guess in its next life it will be doing more of a leisurely cruise along than a hammer-down high speed urgent response.

I was talking to the other half (the financier and TA) yesterday and suggested that once Dennis is back on the road we should take some time off and do a cruise around the NT visiting all of the main fire stations - starting with the four Darwin stations as a 'shakedown' run, then Jabiru, Katherine, Tennant Creek, Alice Springs, Yulara, and perhaps Nhulunbuy on the way home. What a trip that would be!

Another reason for using a course thread has to do with the material you are tapping into. Typically cast aluminium and cast iron will have a course crystaline structure wheras the fine threads are more suited to steel etc which has been rolled or forged somewhere in it's processing. As whitworth supply is difficult the choice points to UNC. BSF tends to be courser than unf so should not be discounted completely if you have access to a supply of taps and bolts

also stainless bolts are suspectable to galling "picking up "on the threads more so than normal hi tensile bolts]
just a thought

And I guess in its next life it will be doing more of a leisurely cruise along than a hammer-down high speed urgent response.

Sorry Bugly, but I don't think you can use "Dennis F1" and "high speed urgent response" in the same sentence. : :.

"Leisurely cruise" would be the turn out description and "slow crawl" at other times. I guess you don't have too many hills around Darwin ??

Sorry Bugly, but I don't think you can use "Dennis F1" and "high speed urgent response" in the same sentence. : :.

"Leisurely cruise" would be the turn out description and "slow crawl" at other times. I guess you don't have too many hills around Darwin ??

Ummm ... ... on cruise control it will be for sure! And hills? Nah, we're known as the flat-landers up here! But I do remember a hill between Darwin and Katherine, another north of Tennant Creek, and a third one just this side of Ally Prings. Can't think of too many more this side of the border though!

Even the cog-shifters on the big rigs hardly get out of top gear once they've reached it!

A little bit of progress this week to report.

At manufacture, Dennis had only a bare minimum of gauges on the dash panel. There was an oil pressure gauge, ammeter and fuel level gauge for the engine, and a water pressure gauge for the pump delivery. The ammeter and oil pressure gauges are unserviceable, so en route from Wagga Tractors are an ammeter, an oil pressure gauge, and a capillary-type water temperature gauge to suit Massey Ferguson which will be fitted to Dennis. This still leaves me to sort out a speedo and a fuel gauge. With these, I will probably need to get the originals repaired, as to find a Dennis speedo would be almost impossible. I

Hi Bugly

The big switch is for the parking/head lights, should have 3 positions. Works anti-clockwise.

The little one above it is usually for the dash liights, but on some it has been for one of the ignition systems!!

The hole is for a red light - on some trucks it had been an "ignition on" indicator, others it was a battery charging light off the regulator.