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New valve guide install
Posted: Tue Mar 02, 2010 8:37 am
'67 Ducati 250 Monza spring valve (non-desmo)
I am installing new bronze valve guides. Heating the head enough so that I will be able to slide the new guides in. Wife has given me the permission to use the crappy household oven. What temperature should I heat it to? 300 degrees to much?
Should I or should I not put the guides in the freezer for 24 hrs to chill them just prior to installing them?
Posted: Wed Mar 03, 2010 9:33 am
Not too sure on the exact temp but I`d like to think an hour or two at 200 C should see her right. I`ve always done the heating with a big gas multi heater and evenly warmed her and concluded she was hot enough after i spat on her and it sizzled off real quick. Beauty of an oven is the heat is nice and even. Mind i`ve had no problems with distortion with the above method but i took care to heat it evenly and wrapped it in a heat proof welding blanket to let her cool nice and slow.
I have found freezing things to have a negligable effect to be honest. Heating can be measured with a micrometer but putting things in the freezer and measuring I saw little, maybe 1/2 a thou but that was about it. Some swear by blasting a CO2 extinguisher over them and that shrinks them. I guess freezing them in the fridge can`t hurt though.
Most important is I found that the guides should still be a very slight interferance fit even with the head hot, You don`t want them popping out just cause the engine got to running temp. To aid this it`s best to have a mandrel that fits in the hole and is stepped over the top of the guide. Also avoid smacking them with a hammer cause this bruises the top of the guide and sometimes makes the valve not go into the hole. You can repair them but why damage them in the first place.
Lastly a good hydraulic press is by far the best way to push them home. Not found in every home work shop, certainly not in mine.
I`ve never done a Duc single, actually never done a Duc valve guide replacement but have done a few other alloy bike heads with this method and they worked out ok.
Posted: Wed Mar 03, 2010 12:44 pm
Oh, nearly forgot. The valve will have to be re-seated. If your lucky you can get away with some pretty vigorous lapping but often the seat will have to be re-cut. If thats the case it`s probably best given to an expert. As with the press not too many home workshops have that sort of stuff on hand.
I do have one in my dream workshop however, right next to the lathe but a little forward of the milling machine that is getting in the way of my Green frame, 750 Sport, 500 Gilera and 750S Guzzi. Like that lady I met in a bar said............in your dreams buddy.............
Posted: Sun Mar 07, 2010 10:59 am
DONE. It is amazing what you can do with the household oven (shhhhh, dont tell the wife). Baked the head at 300F and used 12mm deep well socket, short extension and hammer and tapped it gently in.