help diagnose this engine!
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Joined: Jan 2006
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From: Louisville
help diagnose this engine!
help diagnose this engine!
<HR style="COLOR: #666666" SIZE=1>The engine in question is a flathead caddy, but really this problem is more of a general engine question. The problem is it won't rev above 3100 RPM. If you hold it wide open it revs slower than I would expect and then stops at around 3100 RPM.
The engine is on a stand so it can be ran and tested.
It has new plugs installed.
It has new plug wires.
The carb has been rebuilt.
The fuel was delivered by manual AND electric pumps (tried each way)
The oil was changed.
The water pump and generator turn freely.
The crank can be turned with 40-50 ft. lbs. of force.
At idle it sounds perfect, in fact, it sounds pretty good at all RPMs.
The compression is 110 on most cylinders and 80 on the lowest one.
It has a steady vacum.
It was tried at 100 degrees and 220 degrees. And thru that range.
The timing is set to the factory spec.
The transmission is a hydo-matic.
The engine has good oil pressure.
The distributor advances properly when RPMs come up.
So why won't it rev higher? Also in the vehicle it seemed low on power, but not undriveable.
<HR style="COLOR: #666666" SIZE=1>The engine in question is a flathead caddy, but really this problem is more of a general engine question. The problem is it won't rev above 3100 RPM. If you hold it wide open it revs slower than I would expect and then stops at around 3100 RPM.
The engine is on a stand so it can be ran and tested.
It has new plugs installed.
It has new plug wires.
The carb has been rebuilt.
The fuel was delivered by manual AND electric pumps (tried each way)
The oil was changed.
The water pump and generator turn freely.
The crank can be turned with 40-50 ft. lbs. of force.
At idle it sounds perfect, in fact, it sounds pretty good at all RPMs.
The compression is 110 on most cylinders and 80 on the lowest one.
It has a steady vacum.
It was tried at 100 degrees and 220 degrees. And thru that range.
The timing is set to the factory spec.
The transmission is a hydo-matic.
The engine has good oil pressure.
The distributor advances properly when RPMs come up.
So why won't it rev higher? Also in the vehicle it seemed low on power, but not undriveable.
Last edited by Torque1st; Mar 22, 2006 at 10:05 AM.
Post Fiend
Joined: Jun 2002
Posts: 13,873
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From: Atlanta GA
I thought 3,000-3,500 was about red line for any older flathead, including Fords?
> So why won't it rev higher
Usually because it is not designed to rev higher because of cam design, crank design (too much mass), followed by ignition design, followed by air/fuel limits.
> So why won't it rev higher
Usually because it is not designed to rev higher because of cam design, crank design (too much mass), followed by ignition design, followed by air/fuel limits.
Postmaster
Joined: Mar 2001
Posts: 4,968
Likes: 3
From: So Cal
Is the timing advance in the distributor working? Most of us forget that many of the old distributors need to be oiled. Usually there is a little cap right under the rotor where you add some oil. Or the advance weights may be stuck or the vacuum advance may have lost vacuum etc. Depends on the type.
If the timing does not advance with rpm, then eventually the engine will do just what you are seeing.
Doh, just re-read your post so guess timing advance may not be the issue. Does the advance go far enough. I do not know this engine but some engines will advance quite a bit.
Also is the exhaust restricted? If the exhaust is not flowing well enough it will choke the engine at higher RPMs.
Good Luck,
Jim Henderson
If the timing does not advance with rpm, then eventually the engine will do just what you are seeing.
Doh, just re-read your post so guess timing advance may not be the issue. Does the advance go far enough. I do not know this engine but some engines will advance quite a bit.
Also is the exhaust restricted? If the exhaust is not flowing well enough it will choke the engine at higher RPMs.
Good Luck,
Jim Henderson
Last edited by jim henderson; Mar 23, 2006 at 12:22 PM.
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From: Louisville
The engine *pause for effect* is out of a WWII M5 tank. It has two engines hooked to two transmissions and one final drive unit. The second engine runs VERY well. It will rev slightly above 4000 RPM. It also revs very quickly.
So...
The cam timing sounds like a good place to check, we had discussed it but not acted on it yet. A degree kit has been ordered from Summit. Now we have to learn to degree a flathead.
The RPMs should reach 4000 along with the other engine. A manual on it actually says during break-in it should be run at 4000RPM for 30 min. (that sounds like a lot for a flathead, we try not to even rev that high when driving!)
The advance seems to be working properly, the distributor has been rebuilt and inspected since then with the weights moving when the shft is spun. The exhaust needs to be checked. The muffler looks fine on the outside, I am unsure how old it is. The rest of the exhaust is very short and open.
Thanks for the replies, I will update any progress. If anyone has more thoughts on this issue let me know.
So...
The cam timing sounds like a good place to check, we had discussed it but not acted on it yet. A degree kit has been ordered from Summit. Now we have to learn to degree a flathead.
The RPMs should reach 4000 along with the other engine. A manual on it actually says during break-in it should be run at 4000RPM for 30 min. (that sounds like a lot for a flathead, we try not to even rev that high when driving!)
The advance seems to be working properly, the distributor has been rebuilt and inspected since then with the weights moving when the shft is spun. The exhaust needs to be checked. The muffler looks fine on the outside, I am unsure how old it is. The rest of the exhaust is very short and open.
Thanks for the replies, I will update any progress. If anyone has more thoughts on this issue let me know.
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From: Louisville
[img]file:///C:/Documents%20and%20Settings/cgarreja/My%20Documents/My%20Pictures/my%20tank.jpg[/img]
Probably no critters in the exhaust, it is stored indoors and driven at least every month.
Huh. I cannot seem to post a picture here. I will create a gallery and put it there.
Probably no critters in the exhaust, it is stored indoors and driven at least every month.
Huh. I cannot seem to post a picture here. I will create a gallery and put it there.
Last edited by 1969fordguy; Mar 24, 2006 at 09:01 AM.
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The engine that you have should be the Cadillac 346 Cu In flathead engine. These engines as I remember redline at 3500 RPMs. If your one engine has a govenor, and both should, it will slow the engine down on revving. My thoughts are that the other engine is over revving. Anyway, here is some info on the 346 Caddy engine in case you have none. The info is for the automotive engine which will be almost identical to the M5A1 tank you have.
http://www.secondchancegarage.com/public/490.cfm
Hope this is some help.
http://www.secondchancegarage.com/public/490.cfm
Hope this is some help.
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Sorry, I was wrong, the Caddy engine is governed to 3400 rpms. It makes 110 HP in standard military issue. The other engine is overevving. Here are some stats for you:
http://www.wwiivehicles.com/usa/engines.htm
The engine you have is on the second line. I worked on one of these many years ago for a WWII collector. These engines are pretty neat but a pain to work on in the tank. Luckily, you have all the room in the world to work on it. I can assume that the manual you have is for a different engine. This engine has a 4 1/2" stroke. It may get to 4000 rpms but it isn't going to stay together very long. The wrist pins are only .875 and that ain't much for the stroke and the old cast piston. I wouldn't suggest running it at that rpm if at all.
http://www.wwiivehicles.com/usa/engines.htm
The engine you have is on the second line. I worked on one of these many years ago for a WWII collector. These engines are pretty neat but a pain to work on in the tank. Luckily, you have all the room in the world to work on it. I can assume that the manual you have is for a different engine. This engine has a 4 1/2" stroke. It may get to 4000 rpms but it isn't going to stay together very long. The wrist pins are only .875 and that ain't much for the stroke and the old cast piston. I wouldn't suggest running it at that rpm if at all.
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Flash: it is good to hear that someone else has turned a wrench on one of these engines from a tank before! We are using a manual for the specific tank, it is very detailed. I will try to get the manual number as I don't have it with me now.
The cam degreeing process didn't work quite as well as we had hoped. All of the vavles open the same (measured with a dial caliper) so no cam lobes are wiped out. Without knowing the specs. for when each valve should open it is hard to see if the process is working right or not. I didn't get in on this test, there are several guys in the group that know engines and they worked on it over the weekend, our normal 'tank night' is each Tuesday and I will take another crack at it then. If anyone can explain the process to me I will certainly try it.
In the meantime another engine (probably a whole powerpack) is going to be rebuilt and tested/installed in the tank. We have events to do...
The cam degreeing process didn't work quite as well as we had hoped. All of the vavles open the same (measured with a dial caliper) so no cam lobes are wiped out. Without knowing the specs. for when each valve should open it is hard to see if the process is working right or not. I didn't get in on this test, there are several guys in the group that know engines and they worked on it over the weekend, our normal 'tank night' is each Tuesday and I will take another crack at it then. If anyone can explain the process to me I will certainly try it.
In the meantime another engine (probably a whole powerpack) is going to be rebuilt and tested/installed in the tank. We have events to do...
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