Normal 403 running with a working thermostat is around 80C or 176 F. My 203 has always run around the same. A bit under on a cool day and bit over in the heat.
what he said
great job Dan
Here's an update on my woes with Toots.
So it was running a bit hot and then I noticed that it was blowing past one of the spark plugs.
One of those cracks that go between the plug hole and valve seat had obviously got out of hand.
So my engineer suggested I get a longreach plug and a big washer and use some holden head sealant. I arranged a big washer on a plug as he suggested but I wasn't aware of the ledge down there that the plug is recessed in. Of course the washer sat on the ledge , the plug half engaged in the thread and with a small twist on the plug spanner it dragged the thread out of the head. The engineer wasn't fazed. He suggested I send it to some crowd in Queensland. Needless to say I won't be going back to him or anyone he recommends.
So one night I ripped that head off and installed another with home ground valves and home surfaced face on a block of glass with wet and dry.
It went, but not very well and soon I bought a comp tester to find very bad compression in one cylinder [60psi]and only 90psi in the others.
So yesterday I took that head off to find those cracks had really opened up on this head as well, letting all that compression out.
I think these are the reasons why it has run just that bit hotter under load as it hasn't yet had enough compression to maintain correct power.
I also suspect that the spin on oil filter may be keeping the oil a tad warmer than the original alloy bell which would have acted as a bit of a cooler. I may install an oil cooler later.
I am going to see the man that Robbo goes to for heads, Unlimited Head Jobs in Ashfield and I expect he will have to weld cracks, machine and fit hardened inserts etc. I have four heads to choose from now.
Too bad I had the inserts done on the first head but they have to come out again if that head were to be repaired. Also that head had a stripped exhaust stud and the helicoil failed and then the next insert was already starting to pull out by the time I decommissioned it. Matt says perhaps the alloy has gone soft, which I wasn't aware of. He does a hardness test before any work is begun on these heads.
Someone was suggesting that there is some treatment for such heads. Does anyone know of that?
I spose these things are getting past their useby date but I'm still hoping to get it going right some day.
Then I'll be needing another good engine for the 49er, but one thing at a time.
Thanks for the offer Scotty, I guess the only 403 stuff I have that's any good is gearboxes and diffs but I really don't want to part with them as they are likely to be called upon in the next few years once I'm up and running.
Let me know how much filthy money you might want for it if that were an option.
But I really think these nice 203 heads will come up well so I'll work on building a twin carb manifold after I get some extractors made. Till then the crossflow of the 403 head does little with such restricted exhaust as the standard 203 provides. With a healthy motor I may not even bother with such mods. The extra capacity may well be enough for satisfactory performance once I have compression.
I discovered an interesting thing about both my 203 heads. They are the same pattern for the head gasket as the 403, meaning that the cutout to accommodate the piston is 80mm diameter so it will go straight on[after it's had valve seat inserts at the shop of course]. I have a very dilapidated 203 engine in the shed with the remains of a head gasket still clinging to it. This head gasket also has the 80mm openings though the bores are 75mm. Perhaps it was a 403 gasket or perhaps 203 gaskets are made exactly the same as 403 leaving a bit of space there at the top of the bore? Interesting thought.
I'm sure someone will tell us.