Author Topic: Holt 75 from Germany  (Read 15594 times)

Offline michelko

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Re: Holt 75 from Germany
« Reply #105 on: November 10, 2023, 08:23:27 AM »
Thanks to all for the kind words.
After some lazy time i am realy motivated to finish the project as soon as possible.

Any sugestions about the valve timing? maybe george can give some information?
I am not sure how to set it. The engine should run at low rpm

Regards

Offline gbritnell

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Re: Holt 75 from Germany
« Reply #106 on: November 10, 2023, 11:50:41 AM »
My engine runs best at about 15 degrees BTDC. I can adjust it while the engine is running but it doesn't change the performance much. Unless you advance it too much. If you get it down about 8-10 degrees the engine will run slower but then it won't throttle up very well.  The biggest issue with the engine is when you run it real slow for an extended period of time the fuel will collect in the updraft manifold and when you Rev it up it will smoke for a couple of seconds while it pulls the unburned fuel out of the manifold. I have been able to idle my engine down to 4-5 hundred rpm.


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Offline michelko

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Re: Holt 75 from Germany
« Reply #107 on: November 10, 2023, 08:26:24 PM »
Hi george thanks for your reply.
You wrote about the ignition timing. Thats adjustable without disassemble the engine. So its easy trial and error.
I wouldlike to know the valve timing. Thats not to easy to adjust so it should match as good as possible.
When did your engine starts opening the intake cycle?
Thanks in advance.
Regards

Offline gbritnell

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Re: Holt 75 from Germany
« Reply #108 on: November 11, 2023, 02:11:53 PM »
The camshaft is what is known as a symmetrical cam. The intake cycle and exhaust cycle are identical. There is even overlap at TDC. The way I set the cam to crank relationship is to rotate the engine until the #1 cylinder is at TDC. Adjust the cam position until the intake and exhaust are moving as close to the same as possible. (Intake opening, exhaust closing.) I usually make a mark on the flywheel with a felt tip marker at TDC, with a register point. When the intake opens make another mark. When the exhaust closes make a second mark. They should be evenly split from the TDC mark. The firing will be 360 degrees from this point. (1 revolution)
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Offline michelko

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Re: Holt 75 from Germany
« Reply #109 on: November 11, 2023, 05:22:01 PM »
Perfekt. Thanks.

Offline michelko

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Re: Holt 75 from Germany
« Reply #110 on: November 27, 2023, 02:43:03 PM »
Hi all. Another step is done. Sunnday was piston ring day.
Made them from GGG60 after the Trimble method.
Used my little oven for heat treatment.
I made a little jig to hold the rings for the annealing process.
The rings came out nice.
Happy with the result.

Regards Michael

Offline michelko

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Re: Holt 75 from Germany
« Reply #111 on: December 03, 2023, 03:12:40 PM »
Hi,
today i made the valves.
I used 3mm drillrod for the stem and 9mm for the disk.
The two parts are silversoldered together.
I made a dummy guide from brass to check the funktion. Still waiting for the bronce to make the guides.
I hope it will arrive next week.
The seats will be cut with my selfmade seatcutter.

Michael

Offline RReid

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Re: Holt 75 from Germany
« Reply #112 on: December 03, 2023, 03:41:37 PM »
Very nice work on the valves, Michael! I made a seat cutter just like that one for my last engine, and will use it again on the current one.
Regards,
Ron

Offline Roger B

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Re: Holt 75 from Germany
« Reply #113 on: December 16, 2023, 08:18:52 AM »
Excellent  :praise2: Having a small furnace to heat treat the rings is much better than a gas torch  :ThumbsUp:
Best regards

Roger

Offline michelko

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Re: Holt 75 from Germany
« Reply #114 on: May 13, 2024, 03:29:57 PM »
Hi guys,
slow  and little steps but the project already lives.
I did the pushrods and the bushings for the rockers.
While turning the crank over by hand i can feel the compression.
I am very happy.
I also did the small flywheel. I bought it again from Bengs Modellbau. Because of the smal hub i soldered a bigge Part on both sides.>This will also take the groove for the Waterpump belt and blower belt.
I did the keyway with my cnc mill. Worked realy nice again.

Cheers


 

Offline Admiral_dk

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Re: Holt 75 from Germany
« Reply #115 on: May 13, 2024, 07:26:18 PM »
Not much missing is there ?

As far as I can guess - Inlet system (Carburator + Manifold), Exhaust System + Plumbing for the Cooling System .... or is there more ?

Good looking Parts  :ThumbsUp:

Per

Offline michelko

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Re: Holt 75 from Germany
« Reply #116 on: May 14, 2024, 04:34:38 AM »
And some parts for the ignition.

Offline gbritnell

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Re: Holt 75 from Germany
« Reply #117 on: May 14, 2024, 01:14:28 PM »
Looks great to this point!  A couple of things I noticed. You have no windows in the crankcase.  Not that they are needed but without at least one you have no way to check the oil level. You could add oil through the breather but with a splash oil system you don't want to have too much oil. I keep my oil level high enough so that the bottom of the rods just dip into it by 1-1.5mm. The other thing I noticed is your valve springs look very light. (Wire gauge). I'm sure the engine will start and run but it might not rev up too much. Not trying to be picky, just helpful.
gbritnell
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Offline michelko

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Re: Holt 75 from Germany
« Reply #118 on: May 14, 2024, 03:46:31 PM »
George i did some modifikation to your design.
I build an tube to hold an oil dipstick to check the Level.
I can bee noticed on pic three in my last post.
If this will not work properly i will cut at least one Windows as you mentioned.

 I also use shaft seals from rubber on the crankshaft ends.

Michael

Offline Roger B

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Re: Holt 75 from Germany
« Reply #119 on: May 20, 2024, 09:42:18 AM »
Coming together nicely  :ThumbsUp:  :ThumbsUp:  :)
Best regards

Roger

 

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