Author Topic: Flathead V-8  (Read 142512 times)

Offline gbritnell

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Re: Flathead V-8
« Reply #585 on: March 03, 2016, 05:05:28 PM »
I tried to start my just completed flathead V-8 engine. I got very little action and realized the compression was lower than it should be. When I designed the engine I didn't take into account all the extra volume out over the valves and really didn't do a number calculation as to what the actual compression ration was. As built the engine calculated out to 5.2:1 compression. To remedy this I could go one of two way, new heads or new pistons. I took the easy way and made new pistons. The problem was I had to leave room for the spark plug and the compression I achieved was 6.4:1. I tried to start the engine and it tried to run which was an improvement over the first effort. The next step was to fill up the combustion chambers in the heads. The heads were set up in the original fixtures and the pockets machined out to accept fitted plugs. The plugs were lightly pressed in place and a retaining screw was put in from the water jacket side of the head. (The heads are made in two pieces to form the internal water jacket cavity). I then took a couple of week break to visit family in Florida and with the weather being cold here in Ohio I haven't had an opportunity to restart the engine.
With some time available I took the plunge and started on new high compression heads. These were machined similar to the original set in two pieces but with a simplified parting surface. All the holes were drilled to allow mounting on the fixture plate. The water jacket side of both the lower and upper pieces were machined first, then the fins were cut with a .093 mill saw, offsetting .031 to achieve the .125 fin spacing. The combustion chamber side was machined using the fixture plate and my angle milling table. The valve pockets were cut and then the remainder of the combustion chamber was stepped off to a layout line. The final finishing was done with small mounted stones and riffler files.
These heads will get me up to 8.6:1 so if the final modifications to the original heads won't do the job the new heads will be installed.
The small witness circles in the valve pockets are from when I plunged the cutter in to cut the pockets. The next step was to put in an end mill with a matching radius and clean up the surface. It's hard when you're dealing with .001 here and .001 there to get a good clean up sometimes. The rings are probably no deeper than that but if you try cleaning them up then you go chasing you tail trying to blend into the pocket radius.
gbritnell
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Offline cfellows

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Re: Flathead V-8
« Reply #586 on: March 03, 2016, 05:18:39 PM »
I'm kind of surprised the engine wouldn't run on the lower compression ratio.  Most of my engines have a 5:1 compression ratio but then, my engines are all one or two cylinder.  Maybe the higher number of cylinders cause the engine to run differently...

Chuck
So many projects, so little time...

Offline gbritnell

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Re: Flathead V-8
« Reply #587 on: March 03, 2016, 05:30:14 PM »
Hi Chuck,
I don't think it's strictly a matter of the CR as much as all the friction produced by having 24 piston rings dragging. The engine did try to start but wouldn't keep running so I'm thinking with a boost in compression it will give it a little more kick. Once the rings are broken in and things free up some I would probably be able to go back to the original heads, if need be.
gbritnell
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Offline Zephyrin

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Re: Flathead V-8
« Reply #588 on: March 03, 2016, 06:35:26 PM »
I'm regularly watching your threads and always impressed with your incredible talents and skill for building functionning engine models, thus it is not easy to comment a built of this level.
But it reminds me touble I had in the past with a flat head engine, (a single cylinder one...not a v8 !) namely the combustion chamber did not communicate well with the gas mass in the cylinder, i did not gave enough space around valve to reduce not further the compression ratio, already weak, but it was a mistake, a poor runner. then  I gave some air in the combustion chamber around valves and everything went well, a fine runner with a 1/4.4 compression ratio !

Offline petertha

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Re: Flathead V-8
« Reply #589 on: March 03, 2016, 07:23:07 PM »
I hate to see the extra work George, but I know you'll persevere. When I was drawing up this radial project of mine I was surprised at how seemingly small geometry changes & nooks & crannies can translate into rather significant % CR changes. Being more in the 10:1 ratio (methanol glow) I had to re-think how to ensure I'd have a safe margin to begin with, figuring its easier to add shims & gaskets to lower CR. But options get more limited trying to raise it.

Can you add artificial 'dome-ing' shape to your piston tops to compress up any cavity volume, or is it 'straight top' cylindrical geometry? I've also wondered on the gas side, does higher octane or any other additives work towards helping matters?

Online Roger B

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Re: Flathead V-8
« Reply #590 on: March 03, 2016, 08:11:45 PM »
Sounds a bit of a pain  ::) I'm sure you have already re checked all the basics, but are the ignition timing and cam timing actually what you planned? Is a gear a tooth or two out?

I know you have been following my fun with my vertical engine  :ThumbsUp:
Best regards

Roger

Offline gbritnell

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Re: Flathead V-8
« Reply #591 on: March 03, 2016, 09:50:09 PM »
Hi Roger,
Cam timing is correct. As far as ignition timing I always start at about 15 degrees to get the engines running. From there I adjust to where the engine seems to run it's best and then retard a few degrees.
Other than a couple of engines most always take quite a bit of tinkering, modifying and adjusting to get them to run like I want. With this engine the dual carb setup is something I've never done before so I'm sure it will take a little adjusting also. It's hard when you have to wait for the weather to cooperate but next week were supposed to have a couple of warm days so stay tuned.
gbritnell
Talent unshared is talent wasted.

Offline Don1966

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Re: Flathead V-8
« Reply #592 on: March 04, 2016, 12:15:29 AM »
Just tuned in on the engine post George and sorry to hear your still having issues. But I guess it's isn't something you haven't dealt with before. We will be waiting for the outcome and have no doubt you will prevail.

Don

Offline sshire

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Re: Flathead V-8
« Reply #593 on: March 04, 2016, 12:26:30 PM »
George
You know, and we all know, that it's going to run in superb fashion. My vote is for the drag of all those "new" rings. Once broken in, I'm betting it will run like your other engines when I see it at NAMES.
Best,
Stan

Offline fumopuc

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Re: Flathead V-8
« Reply #594 on: March 04, 2016, 08:21:45 PM »
 Hi George, take the time needed for necessary R&D work and you will get it. Waiting with patience for your next steps.
Kind Regards
Achim

Offline CHP

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Re: Flathead V-8
« Reply #595 on: March 04, 2016, 11:52:56 PM »
George
I feel sorry for you  :'( having to change so wonderful parts   :'(

now that I'm done crying ;) if I can suggest something, especially because
you think it's a matter of c/r

I would try it with different kind of fuel, gas, super, ethanol, in your case
I would go with regular with octane booster if this solve your problem
you will be sure you need more c/r

good luck
 :cheers:
12x36 lathe,Seig7x10 lathe, Taig lathe
9x29 Mill, Emco 55 CNC mill.......

Offline Mayhugh1

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Re: Flathead V-8
« Reply #596 on: June 21, 2016, 10:23:06 PM »
George,
Have you been able to make any more progress, either forward or backward, on your flat head?
Terry

Offline gbritnell

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Re: Flathead V-8
« Reply #597 on: June 22, 2016, 03:16:13 AM »
Terry,
Thanks so much for your interest. This one really has me stymied! I've done head changes, piston changes and ring changes. I'm amassing a stack of experimental parts that's ludicrous.
Here's what seems to be the problem currently. I started wth the first set of Pistons having just 2 compression rings, made to my own sizes. When I spun the engine in the lathe to break things in I was getting oil past the rings. Even after extended run-in time. When I put in the second set of Pistons I went strictly with Trimbles's numbers, and added oil rings. I have never made oil rings this small (.830 bore) so they were kind of experimental in design. Run-in seemed to produce the same results, oil migrating past the rings. At this point I started from square one. I took the whole engine apart, made a new lap and meticulously honed each cylinder until they were round and true to each other with the measuring tools I have available. This made the bores .0015 larger than original which necessitated new pistons, and rings.
I made the new rings the same dimensions as the previous set, except that they were made the new bore size. Same results! Once again I took out all the pistons and rods, took off the oil rings, made a chucking fixture to hold the pistons true and recut the oil ring grooves for slightly wider, stiffer rings. This explanation is actually the condensed version. I have taken the screws in and out of the block so many times that the threads will probably start to fail in the near future.
When I try to run the engine it has good vacuum, good compression, adjusted timing, my best ignition box etc. etc. It will try to start but won't make enough power to keep running. When I continue to crank it over it becomes flooded. The last time it did that I let it sit on the bench overnight and the next day when I pulled the heads the cylinders were still full of oily gas so the rings are sealed otherwise it would have leaked back into the crankcase.
If I could just get it to run for 10 seconds on it's own I could better diagnose the problems.
gbritnell
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Online Roger B

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Re: Flathead V-8
« Reply #598 on: June 22, 2016, 07:15:39 AM »
Two really basic questions that I am sure you have addressed:

Is the oil level in the sump too high?

Is the crankcase breather large enough?
Best regards

Roger

Offline Hopper

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Re: Flathead V-8
« Reply #599 on: June 22, 2016, 09:36:31 AM »
GB, be careful not to make your combustion chambers too small, ie compression too high, or you will impede gas flow in and out of the cylinder.
I mess about with old Flathead Harley engines and the rule of thumb is a maximum compression of 6:1 before you start to restrict gas flow in the "throat" between the valve pocket and the cylinder. The other critical area is to leave clearance around the back side of the valves and above the valves so gas can flow up and over the valve from the masked side.

Harley raced Flathead engines right up to 1969, at which point they were lapping the Daytona Speed bowl at 149.9mph with a compression of 5:1. Gas flow was found to be more important than compression.
On their street bikes, standard compression was 6:1 and the military models were 5:1 for low grade fuel.

I know the (full sized) Ford Flathead guys still use Harley KR racer combustion chamber shapes as the ultimate role model when building performance engines.

If you google Harley KR combustion chamber, there is a wealth of information out there ranging from downloads of the original race bike manuals (including detailed drawings of combustion chambers) to discussion of what guys in vintage racing are doing today.

How relevant this full sized stuff is to model-sized engines I don't have the miniature experience to know firsthand but it might be worth keeping in mind.

And beware of getting addicted to the dark art of squeezing maximum performance out of this least efficient of combustion chamber formats!
« Last Edit: June 22, 2016, 09:44:28 AM by Hopper »