Balance shafts and motor mounts

[DM333]

Hey guys, this is my first posting, previously i've only been on Rennlist and have only been a DIY porsche owner since this last march when i bought my 86 944 NA with 153k miles on it to turn it into a SCCA, NASA and PCA track car, but i recently had a massive engine failure in my '86 944 NA that required an engine replacement or over $3k in repairs, i found an 85.5 engine from a salvage yard nearby with almost identical milage and was able to have a local shop, one that a friend works at, swap the engine for less than the cost of repairing the original engine, since i've gotten the car back, it fires right up, but it has a few issues, the most concering issues is worrying engine vibrations from balance shafts that are out of time and the original motor mounts that are shot, and an oil leak that appears to be located somewhere just barely rear and up from the power steering motor assembly. the oil leak is hard to find because when the engine runs it seems to spray the oil rather than leak it, it started as a drip but has quickly gotten worse. as far as the vibrations goes, i've spoken with a friend that races SCCA and NASA events in a Mitsu Evo who says i should buy a balance shaft delete kit and semi solid motor mounts, ones like the lindsey racing ultra mount, and then send it to a mechanic shop to find the oil leak. i've also suspected that maybe the leak and out of time BS's are related and maybe the leak is coming from the BS located on the driver side, behind the power steering pump assembly. ive read a few threads about the dangers of balance shaft deletes, and how they should only be used on track cars, which mine is, with the exception of coming to and from the track. i just wanted your thoughts on using a balance shaft delte (because it may solve the oil leak, reliability and vibration issues) along with a semi solid mount like the Lindsey racing ultra mount, on a track day oriented car. i havent seen anyone say they use both mods on their car, which is causing me to suspect that it is simply not a good idea on any set up, or maybe the subject just hasnt come up yet. as always, thank you for your help.

[CHICKS]

Just do it, i'll be fine. It'll vibrate the **** out of you, and bolts will come loose. The only thing you would need to do is an oil pickup tube support. You really don't want that to crack. Since you're doing the support, you should do rod bearings, and nuts, pan gasket, and this, and that, some more of this. When you get that far, you might as well rebuild the engine and fix the oil leaks. Return the oil tube pick up support. Have $10k into a $2k 944. Repeat the cycle like a laundry mat....

Paragon- Products Oil Tube Support Bracket

[flash968]

i tried those ultra mounts. vibrated the hell out of me. the sleeve they use bottoms out, making the rubber useless. the threaded rod they use is pure crap. i think it's grade 2 or something. they should have used a high grade bolt and locking nut.

a balance shaft delete will result in harmonics. yes, there is some frictional loss that can mean a couple of hp very high up, but it can also mean a loss of power if things are not perfect, as you would then have things "fighting each other" due to being out of balance.

[Rasta Monsta]

BS delete is utterly foolish for a casual track car. I wouldn't even do it on my race car.

[flash968]

me either, but i know that there are a couple of guys who have realized the benefits. expensive motors though, as they really had to nail everything in order to avoid the power losses. definitely not for the faint of heart or light of budget. it's not the cost of the kit. it's the cost of properly implementing it.

[v2rocket_aka944]

Re-timing the balance shafts is too easy to justify a delete kit.
Not to mention it will not be as nice to drive without the shafts running, and will cause parts to fail.

There isn't enough power freed up by their deletion to justify it.
Just fix it.

[edredas]

There were millions of inline four cylinders engines built without balance shafts. Some are still built today and much larger than our 2.5 liter engines. Many tractors reached 6 liters and an not a single bolt ever came loose. This is all just speculation from people that have no idea what they are talking about. All engines to some degree have this vibration. Ask any trained engine builder, and he will tell you that they are for engine refinement and passenger comfort. Engineer have written many books on this topic, so read those, and don't parrot people that don't know what they are talking about.

[v2rocket_aka944]

Originally Posted by edredas

There were millions of inline four cylinders engines built without balance shafts. Some are still built today and much larger than our 2.5 liter engines. Many tractors reached 6 liters and an not a single bolt ever came loose. This is all just speculation from people that have no idea what they are talking about. All engines to some degree have this vibration. Ask any trained engine builder, and he will tell you that they are for engine refinement and passenger comfort. Engineer have written many books on this topic, so read those, and don't parrot people that don't know what they are talking about.

A 6 liter tractor has hugely long conrods (which helps with the vibes) and doesn't rev past 2000RPM, if even that high. The vibrations aren't so noticeable there.

Try driving with your B-shafts disconnected or misaligned and it is properly annoying to drive. It buzzes like you've got a bee in your nose. And the multitudes of broken oil-pickup tubes in 944 engines that had this done proves the point.

[flash968]

yup - it's all about harmonics. any engineer can tell you all about it.

some engines have a harmonic balancer. some have balance shafts. some have both that and balance shafts. some have dual mass flywheels. but there is almost always a mechanism to deal with second order harmonics.

[H.F.944]

Originally Posted by edredas

There were millions of inline four cylinders engines built without balance shafts. Some are still built today and much larger than our 2.5 liter engines. Many tractors reached 6 liters and an not a single bolt ever came loose. This is all just speculation from people that have no idea what they are talking about. All engines to some degree have this vibration. Ask any trained engine builder, and he will tell you that they are for engine refinement and passenger comfort. Engineer have written many books on this topic, so read those, and don't parrot people that don't know what they are talking about.

someone called "edredas" talked about this topic on the 924Board.org (subject: Balance Shaft Discussion).
Very interesting write-up from my point of view. It's worth reading.

[edredas]

V2, I don't have balance-shafts on my car, and haven't for over a decade. There is no locktie used on any of my bolts and I don't loose sleep because I don't have a reinforced oil pickup tube. You don't understand what this vibration is if you think that adding reciprocating mass; i.e. thicking up connecting rods will "help with the vibration". No, that would make it worse. As I said, there were Millions of large inline-fours build without balance shafts. If you don't like the tractor example, how about the 5.7 liter that Bentley built for their cars. It didn't have balance shafts and spun to 6000 rpm.

[flash968]

every four cylinder i have ever seen, in 30 years of doing this, has had some form of a dampening mechanism for dealing with harmonics. most cars use a harmonic balancer. this one uses balance shafts, originating from the mitsubishi design. balance shafts are used in a number of engines. google it. you'll find it's actually a fairly common practice for coping with second order harmonics.

a quick google search of "engine balance shaft" will also turn up a number of sites which explain what these do, and why you don't want to delete them.

don't take my word for it. google it yourself. there is a ton of stuff out there. it's not hard to find.

[edredas]

Flash, the 2.5 liter in the Dodge Dakota still don't have them.

[v2rocket_aka944]

Originally Posted by edredas

V2, I don't have balance-shafts on my car, and haven't for over a decade. There is no locktie used on any of my bolts and I don't loose sleep because I don't have a reinforced oil pickup tube. You don't understand what this vibration is if you think that adding reciprocating mass; i.e. thicking up connecting rods will "help with the vibration". No, that would make it worse. As I said, there were Millions of large inline-fours build without balance shafts. If you don't like the tractor example, how about the 5.7 liter that Bentley built for their cars. It didn't have balance shafts and spun to 6000 rpm.

I guess the best example would be the 944 factory racecars (and the 924GTR or whatever it was called with the 2.5 16v turbo in 1981)...all these cars kept balance shafts despite needing every last bit of power to be competitive in their class...why?

[edredas]

According to Porsche, the "compensating shafts"; (as they are called in the workshop manual) sap about 5 hp. So, they do not "add" power. Also, up until the 1970's balance-shafts were a joke and considered to be a liability since they could fail, and often did. Perhaps Porsche wanted to prove how good they were by racing with them, but that is just speculation on my part.

Porsche did not design them, they are nothing more that Mitsubishi "silent shafts", and this exact design is rarely used today. Wikipedia can get you all caught up. They are for Noise Harshness and vibration, i.e. passenger comfort. Not for anything else, Period.

[flash968]

maybe the dakota doesn't have balance shafts, and i'm sure there are plenty of others, but i'll bet it has either a harmonic balancer, or another harmonic compensating device, specifically to deal with the same issues.

i don't know where you get your information, and i think you are just trying to justify or rationalize something you have done to your car, but many motors use balance shafts. GM used them a lot in their cars, at least up until 2009, and ford in their trucks.

bmw is using them in their new N20 turbo I-4, and makes a big deal about it.

i'm quite sure many other manufacturers are using them. why? because they work.

over the last 11 years i've read a lot about people who have tried to delete them. the results have not been stellar.

no, they do not "add" power. what they do is prevent a loss due to imbalance. any vibration reduces the energy that can be transmitted. to get rid of that, you would have to do a lot of work, at great expense, to get everything balanced perfectly, each chamber matched, each piston fitted to exactly the same height, and still you would have harmonics.

things were so bad by the time they got to the S2 that they added a harmonic balancer to the front. in the 968, they went to a dual mass flywheel, in addition to the balance shafts.

[edredas]

Flash, as I mentioned, there are a lot of books on this subject. You don't have to take my word for it, but in your posts, you are confusing very different things. Balance shafts are just vibrators meant to make the engine feel a little smoother. Not having them doesn't mean anything.

[flash968]

as a mechanical engineer, i can tell you that you are wrong. you can calculate the harmonics. you can calculate the effects of the shafts (duh - that's how they design them. it's not guesswork). 30 years ago i could have calculated it too. now, i'd have to go back to my books. i did find a site with the math on it though. it wasn't hard to find, and i'd suggest reading it. the math doesn't lie.

it is also very easy to see the effect of a deletion on an engine, even for the average driver. for example, you can tell right away if you've ever had the balance belt belt break, or jump a tooth. in addition to the vibrations, the car will feel flat by comparison. it's a measurable difference in performance. it's not unlike having an unbalanced flywheel/clutch assembly.

this is why i hate the internet. people take bits and pieces and apply them out of context.

i can see that i, nor anybody else who has been doing this for a while, is going to convince you otherwise though, so i'm going to leave this alone now.

to anybody else, please do the reading i pointed to. it will tell you the realities.

[edredas]

Sorry, but this only heard in the 944 community. Most other car guys are smart enough to read a book and figure out how things work, but instead, we have guys that think they know everything but are actually just rambling about non-sense. I build engines for a living and see engines without balance-shafts from the factory all the time. A flat-plane V8 is like two inline fours running at the same time, but it is rare to see balance shafts on them... so rather than arguing with me, why don't you call those automotive engineers and tell them how wrong they are.

[flash968]

of course there are engines without balance shafts. that is only one way of dealing with the realities of harmonics.

again, i am quite certain they deal with the harmonics in another fashion, and you have failed to challenge that, or provide any example of an engine that does nothing about harmonics.

but, as i said, nothing i say will sink in or convince you, so i'm not going to try anymore. i've been doing this professionally for 30 years. i've seen pretty much everything.

why don't you ring up BMW and tell them they wasted the millions on development of their new 4 cylinder motor? maybe you should tell them how to do it. it's not like they make some of the best running engines in the world, and could build it any way they wanted or anything.

by the way, most 4 cylinder motors over 2 liters usually have balance shafts. not that i'm a big wikipedia fan, but here:

Balance shaft - Wikipedia, the free encyclopedia