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Hup Model 20 pistons


1912Minerva
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Hi All,

Getting ready to reassemble my Model 20 motor after fixing a water leak in the combustion chamber of No. 3 cylinder when we noticed that the gudgeon pins (wrist pins) in the pistons do not have the normal circlips to contain the gudgeon pin within the piston. There is a pinch bolt securing the gudgeon pin on the underside of the piston. We looked at adding circlips but noticed that when we moved the pistons on their gudgeons to a point where the circlips would fit in the grooves in the piston, the pistons seemed out of alignment with the holes in the crankcase. Does this seem strange to anyone? Is there any issue with running the motor with out circlips? Maybe the bolt holding the piston to the gudgeon is not centred properly?

Attached are a few images so you can see what I'm talking about.

Any thoughts / comments appreciated.

Regards,

Andrew.

post-91280-143142362222_thumb.jpg

post-91280-143142362211_thumb.jpg

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And...on a related topic! The valves on my motor seem very loose, they are Australian made DUFOR N valves that look to have been turned down to 7.8mm. I would be interested in what type of valves people are running in their Model 20's - will Model T valves work?

Cheers,

Andrew.

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G,day Andrew and Huppers. In one of our engines we have Holden valves the other engine has Ford Falcon .We used the spring caps and retaining cotters that matched the valves after adjusting them to length. We scrapped the fibre blocks and the screwed retainers and threaded the tappets to take adjustable grade 5 cap screws the same as a model 32.Sorry I don't know the models the valves came from as we just went over to the head shop and got them from the scrap drum in which there were hundreds and all for free. Use the ones not attracted to your magnet in the exhaust. On the first engine we made the pins a press fit in the rods and still used the circlips ,on the second engine we used the original system but with circlips as well. In both engines the pistons are NOS MOPAR. plus 030. I would not use the method of locking the pin into one boss of the piston better to use the original Hup style with the pin locked to the rod . use the original square head set screws if you have them. The pins can be deep dimpled to take them with a masonary bit in the drill press. allow at least an eighth of an inch clearance each side of the pin boss in the piston to the conrod.If the pins don't suit the pistons in length be sure they don't protrude beyond the skirts to rub the new bores.Good luck with the assembling. Max Burke Nulkaba 2325 Australia

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  • 3 weeks later...

Hi All,

Thanks Max for your reply - most useful.

I think I am getting there but have now completely disassembled the pistons and have found that the big end caps, although babbitted nicely, don't have any oil grooves located in the babbit bearing to spread oil across the bearing face. See pic below. I am assuming they should, to allow oil to get every where that it needs to? If I am correct in thinking this, what is the suggested pattern for the grooves? A friend has suggested a V-shape to take the oil from the inlet hole towards the edges of the bearing.

Also, my big end caps were fitted with Nylock nuts - do folk visiting this forum think they will be OK? (As opposed to locktite, wired up nuts etc.)

Thank you and regards,

Andrew.

post-91280-14314239073_thumb.jpg

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G,day all.Andrew there is no need to groove the metal in the rod but at the joining face file or cut a chamfer in the white metal about 3/32 but don't bring it out to the edge, leave about a 1/4 inch at each end, do the same with the cap. Now grab the dipper in the vyce and cut an X in the cap metal so the legs of the X run into the chamfers with the cross over the dipper hole. job done 3 to go. Max Burke Nulkaba 2325 Australia

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Hi Max - thanks again for that. Another q (for anyone!) - what arrangement do you use for the nuts on the big ends? My engine has nylock nuts fitted which seem to be OK but am wondering whether ordinary nuts with Loctite would be better? Does anyone wire the nuts?

Regards to all.

Cheers,

Andrew.

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