The Tom Thatch Modification

[Dave Neptune]

Wear?

Tom, re your additional power concern regrding the crank flexing. I kinda have my doubts about the crank flex at the HP we are using which is around 20 on the hi side with the direct drives in cruise mode at around 19/2100 RPM's. I have seen crank flex and twist as you probably know in a hi output engine. However I would give serious consideration to to much timing due to the setting methods and a lot of inexperienced mechanics. I'm not talking about detonation but a bit to much lead causing a minor shock when the fuel is lit. I have seen many many bearing sets with excessive wear at the bottom center of the bearing due to this. You probably saw many engines that felt spunky because of to much lead when it was actually running rough due to a bit to much when the engine was maxed out at WOT.
RE more power I'm pretty much dreamin here. I do feel we could gain a bit of torque and a bit of power with a profile ground fo 2500 RPM instead of 3500 RPM. Im' sure you have seen many an engine with to much cam for what was being asked of the engine. I'm talking 3~4 more HP at the same cruising RPM's. There have been many gains in profiles since the 20's when these beasties were developed. Like I said though I'm dreaminon this subject.
If I ever wind up rebuilding mine and the cam needs regrinding I would seek a different profile and try it. Isky has done many a truck cam for me over the years and if they or someone else had someting available it may be a minor improvement.


Dave Neptune

[tartansailboat]

Thatch mod

Question for Don. I have just finished my springtime acid flush and saw this proposed modification for the cooling system piping. Sounds OK but do you "officially" sanction it? These A4's have been running for many years woth the present configuration and aside from occasional clogs in the elbow at the output of the manifold, they seem to do OK. Do you see any downsides to the cooling system change? No offense meant to Tom, just asking the obvious question before I change over.

[thatch]

Dave,
The wear I was referring to showed up recently on two engines in the group, where the owners were having trouble reaching what we consider "normal" cruising RPM's (2000-2500). It sounded like they were in a good state of tune, (probably power tuned for max rpm) but were most likely running too much prop, kind of like going uphill in high gear. Moving on to the design of the A4 crankshaft, there is a sizeable center counterweight that leads me to believe that Universal was probably relying on centrifugal force at the higher rpm ranges to maintain crankshaft straightness, in the absence of a center main. Having said this and if my assumption is correct, adding a few more horsepower would probably not do any harm as long as it was used at higher rpm's and not down at the 1500 rpm range. One item that is generally ignored but one that I feel is probably the biggest culprit in this odd wear syndrome, is ignition timing. As you are well aware, running an engine at borderline detonation may produce the most horsepower available, but is never a good practice, particularly in an engine that will be run at the same cruising rpm for hours on end. Universal did a very poor job of giving us good timing marks with which to accurately "time" our engines, in my opinion. I had mentioned previousely that I had done some research comparing the A4 to other engines and will post some interesting numbers if anyone is interested.
Tom

[roadnsky]

...I had mentioned previousely that I had done some research comparing the A4 to other engines and will post some interesting numbers if anyone is interested.

Tom-
Consider this as an 'official' request...
POST away!

[thatch]

Tartansailboat,
Please pardon me for "butting in" and there is no offence taken for your asking Don's opinion. However, I hate to see Don being put in a position to potentially have to critisize universals original design. My design change, (which I consider very minor)of rerouting the coolant flow comes from many years of converting automotive engines to marine use, and having to design the cooling systems from the ground up in many cases. If Don choses to give an opinion, (in either direction) I will most certainly respect it.
Tom

[thatch]

"Done deal"

Jerry,
I will gather my notes and post them soon. I just hope I don't put too many people to sleep.
Tom

[Dave Neptune]

Change

Tom et all, the design of the manifold is pretty symetric and is capable of being used with the exhaust at the flywheel end in some cases. So I would think that they cast the water jackets in the same manner. The water flow in most older engines was always from the bottom up so to speak and is a good idea on non presurized systems. Pushing the water up hill just makes sence and I doubt it would make much differance either way~~ie~~ with the Tom's mod I think the KRAP will just collect at the new exit end just as it did goiing the other way The reason for getting flakes in the system upon reversal of the flow is as the pile of KRAP is pushed in the opposite direction some will pass through as they begin plugging the new end. You will flush things out whenever you reverse the flow. My $02 on the mod and I will be doing the mod on mine in a week or so. It would be nice to talk to some of the ole timmer mechanics to see if they had any missgivings about it or experience with it.
I think I just have a bit more confidence in the rigidity of the A-4 crank. Although you make a good point with the center counter weight (especially lugging), I feel the crank is short enough to bear a bit more load at the lower RPM's we use. However the scaling up in cylinder preassures at a more rapid rate to get an increase in power will need to be much more closely monitored as to the advance curve and the timing would require a more closely controlled setting. All of this would be doable for the more experienced as we set them now via "ear", however if the timing is to far advanced or the curve to quick we may get a spot where the crank could shudder a bit and that's not good. Like I said I would be willing to try a different cam grind if I could find someone to do it if the cam needs a regrind or not. In my case I'm sure it does due to water damage to the cam when I bought her.

Dave Neptune

[hanleyclifford]

Dave,
The wear I was referring to showed up recently on two engines in the group, where the owners were having trouble reaching what we consider "normal" cruising RPM's (2000-2500). It sounded like they were in a good state of tune, (probably power tuned for max rpm) but were most likely running too much prop, kind of like going uphill in high gear. Moving on to the design of the A4 crankshaft, there is a sizeable center counterweight that leads me to believe that Universal was probably relying on centrifugal force at the higher rpm ranges to maintain crankshaft straightness, in the absence of a center main. Having said this and if my assumption is correct, adding a few more horsepower would probably not do any harm as long as it was used at higher rpm's and not down at the 1500 rpm range. One item that is generally ignored but one that I feel is probably the biggest culprit in this odd wear syndrome, is ignition timing. As you are well aware, running an engine at borderline detonation may produce the most horsepower available, but is never a good practice, particularly in an engine that will be run at the same cruising rpm for hours on end. Universal did a very poor job of giving us good timing marks with which to accurately "time" our engines, in my opinion. I had mentioned previousely that I had done some research comparing the A4 to other engines and will post some interesting numbers if anyone is interested.
Tom

Tom - Your discussion is exactly why I am opposed to so- called "power tuning" of ignition timing. Timing should be set with a timing light to factory specification without regard for RPM or engine performance.

[Don Moyer]

Tom,

I applaud your idea of reversing the coolant flow through your manifold, and I feel a bit remiss in not doing so earlier (without the need to be prompted). It will no doubt eliminate trapped air that can collect in the front of the manifold, and I love the fact that it only requires a couple feet of hose to implement.

For now, and only because of our historical effort to retain the original appearance and function of the O.E.M. configuration whenever possible, we plan to hang on to the traditional setup in our exchange engines. We will however, enthusiastically endorse your modification along with any others that enhance the performance and/or maintainability of the Atomic 4.

Don

[Dave Neptune]

Setting the beastie

Hanley I totally agree on the timing concerns you express. I was tqught old school on many duty rated engines without marks (mostly gas compressors and irrigation engines) to set them just as Universal states BUT I was also taught that when you achieved the max rpm via "power timing" was to ALWAYS back it off a "tic" before tightening the distributor. That is the way I set my beastie when I make changes in prop or playing with the carb jetting.
I like the idea of marking the aux pulley for timing as we have seen done on this sight and a great idea it was. My concern is can the inexperienced mechanic do a good job of being accurate at finding true TDC.
I will be marking mine hopefully this year mostly for curiosity about the centrifugal advance curve and where and at what RPM it is against the stops.

This is fun!
Dave Neptune

[hanleyclifford]

Dave - I think each distributor should be checked for advance curve as I have found considerable variation in this area. I like to clean and oil the area around the weights and springs because of possible sticking. I do believe that every engine should be clearly labeled for TDC. Those who don't have the experience to do it themselves should get it done by an A4 mechanic. I am especially concerned about this because of the distances I motor.

[edwardc]

A second reason for reversing the coolant flow comes from thermodynamics.

In most A4s (but not the V-drive models), the exhaust exits at the rear of the engine. With the standard plumbing, this has both exhaust and coolant flowing in the same direction.

Way back in college, I remember having to do the calculations for heat transfer for both cases: parallel flow and counter flow. It turns out that, all other things being equal, the counterflow case always has greater heat transfer. Whether it would be a significant amount or not in our case remains to be seen.

So this sounds like a win-win modification. No trapped air pockets AND better heat transfer!

The V-drive case is not so cut-and-dried. Since the exhaust in that configuration is taken from the front of the engine, the flows are already counterflow, but the coolant is still going downhill. You can get counterflow OR uphill, but not both.

[sastanley]

Ed, the solution for that is the MMI replacement manifold that Dave Neptune alluded to. Either end of the manifold will accept the exhaust flange, and it has a block off plate that you install in the other end.

Thanks for the info from the 'more experienced' bunch regarding timing. I plan to implement Tom's timing marks among my many other projects. Since I cut a hole in my boat so I can access the flywheel roll pin, I can get close to TDC..it seems the absolute test is to have a small screwdriver or popsicle stick in the cylinder resting on the piston and watch it rise as you get close to TDC..would this be accurate enough?

[thatch]

Don,
Thank you for your courteous responce to the design question dropped in your lap. I too agree that the improvement would have to be considered minimal except in cases where the engine were to be operated at or near the maximum 15 degree angle that Universal specifies as their limit. In these cases it might be a good idea to recommend that users change the coolant flow in the manifold. This change could actually go hand in hand with your improved oiling modification of the accessory drive unit.
Sincerely, Tom Thatcher

[thatch]

Dave and Hanley,
Of all of the engine related tuning topics discussed, ignition timing is probably the leased understood and potentially most destructive of all. Having seen the damageing results of excessive timing in automotive engines, I naturally approached the A4, insisting that my engine was running near factory specs. In the case of my Catalina 30, the TDC marker is hidden unless an access hole is drilled in the panel covering the flywheel. Perhaps, at this point we should put our heads together and develope a timing mark modification that others could easily install. Any thoughts ?.
Tom