ph31mwl

I went to the machine shop a few days ago that is going to “freshen” my 327 engine. I am giving him a short block and he will remove the pistons and crank. The engine is going to be balanced and the flywheel, pressure plate and clutch balanced to the crank. He is also going to reassemble the short block. He suggested that since I am going to put in a hydraulic roller cam that they do it (good idea, I don’t know anything about the buttons or what is involved with a roller cam). I then asked about the harmonic balancer I need to give him. He said that since I am balancing the engine I do not have to use an 8 inch balance but can use a 6 inch balancer. I am building the engine with the Edelbrock hydraulic cam, matching heads, intake and carb. Edelbrock said that it should be around 370HP.

Is a 6 inch balancer sufficient or should I use an 8 inch?

Greatly appreciate your input.

Mark

Mossy66

Not knowing any better, I would use whatever size the engine came with, or is supposed to have. What timing tab are you using?


Gerry

MikeM

The harmonic balancer has nothing to do with engine balance and everything to do with canceling out torsional vibrations of the crankshaft.

ph31mwl

Thank you gentlemen. From what I have read on the Forum, an 8 inch balancer is used when the HP goes over 300. So since I am going to around 370HP then I will need to get an 8 inch.

Thank you for your responses.

Mark

GUSTO14

I believe that John Z posted something in the past regarding the differences of the two harmonic balancers'. As I recall the original balancer is designed around a rather narrow RPM range. One for the lower hp engines and one for the higher hp engines.

I think you will find that many of the new modern harmonic balancers available today are designed around a much wider range of RPM's. ATI, Fluidampr and TCI all produce high quality dampers that don't just dampen vibrations, they absorb them. As a result, engine crankshaft and bearing life along with valve-train stability can be substantially increased.

If you are not building the engine around NCRS judging standards, you may want to talk to your builder and see what balancer he recommends for an engine with the cam shaft you are using.

Good luck... GUSTO

Bluestripe67

FWIW, when the machine shop did all of my machine work on my 327, (I did complete assembly) it was recommended that the stock (6"/300hp) damper be used. I'm getting 390-400hp from my rebuild. At 112k miles later, zero issues, smooth reving. A heaver damper is just more weight for the crank too spin. Dennis

MikeM

The weight/diameter of the balancer has NOTHING to do with horsepower. It has to do with canceling out torsional twisting of the crankshaft which usually peaks at the rpm of maximum engine torque.

If you don't run the engine as a rule close to the rpm of maximum torque, I probably wouldn't worry too much about which balancer to use.

Tuning the balancer to the needs of individual custom built engines is probably several pay grades above anyone I know of on this forum.

pop23235

Every rotating device will exibit a natural frequency. With the Chevy SB (operating from a 45 year ago memory here) there is a natural harmonic on the crank at ~1500 rpm and then ~3000 rpm, then ~4500 rpm....on and on. So it depends on the rpm you expect to see and how often till the crank breaks. The 6" is sufficient to cover the 3K and 1.5K. Chevy added the 8" for the 4.5K and 6K harmonics. Now don't take the mathematical number to the bank. Memory is a strange thing, but the concept is correct.

MikeM

Based on my limited knowledge on the subject, this sounds correct.

FWIW, most 283 engines used a forged crank. Later ones used a cast crank. At some point, Chevy decided one or the other didn't need a harmonic balancer and just used a solid steel hub to fasten the crank pulley too.

JohnZ

That was only used on some low-performance passenger car 283's; all Corvette engines had conventional harmonic dampers.

GOSFAST

The crank material determines (to a degree) the size of the damper. If you're using a "cast" crank you should stay with a larger damper, for a "steel" one any size will be good.

On a higher end build with a steel crank the 6.000" piece is fine, less rotating mass.

The cam button is required with any retro-hyd-roller OR solid-roller cam build. The stock timing cover works fine. We've found most true-roller buttons won't fit with the factory "tin" t/covers so we use a teflon piece for these builds. If you're planning a cast aluminum cover you'll need a "short" (roller) button and it will require some "fitting". You need about .005" cam end play!

Thanks, Gary in N.Y.

P.S. You don't say the year? or cast or steel crank?? If it's early, have the shop drill/tap for a damper bolt!The only "tip" I would add, make sure you can get the corresponding timing pointer to go with your damper size! This could become an issue later.

MikeM

Yeah, all Corvette 283's had steel cranks. The cast crank started in late '64 on '65 model pass cars.

MikeM

Could you possibly clue me in why my (steel) crankshaft broke in my SHP 327 in my '56 Bel Air with 4.56 gears while I was cruising to work one morning at about 4000 rpm? That is the same rpm I normally drove on the highway. Just driving along steady and it let loose between the 4th and 5th main journals.

Five of my friends had the same misfortune with the same powertrain.

The common denominators? All of us had 4.56 gears and all of us used the small 265 balancer on our replacement SHP replacement engines.

Now, if I'd had a different rear gear and changed my cruise rpm, I don't believe I'd have a problem. See previous posts.

ph31mwl

Well, I finally had a chance to come back to the Forum to read responses (and thank you all for your input) and to get to the garage and see exactly what I have. Since I am building a 6500 RPM engine but will not be racing it or doing any street drag racing or spending a lot of time at the high end of the RPM range I am comfortable (based on all the research I have been doing on balancer size) using the stock balancer. I also talked to a friend of mine who years ago built a very hot solid lifter 327 and has had no problems with the stock balancer which is not an 8 inch balancer. I went out today and found the balancer that I took off the engine earlier this year. It is 6 inches in diameter and fits just under the timing tab on the timing chain cover. By the way, the nose of the crank is drilled and has threads for a bolt. Everything I have read indicated that the stock balancer is 6 3/4”. I do not think I can use the current 6” balancer because there is some rubber missing and a rivet or two were coming loose. I have been trying to research what engines the 6” balancer was on but am unable to find anything specific.

This whole balancer thing is making me nuts. I am a body and paint hobby guy and little technical things like this I just do not understand.

Summit has lots of balancers by lots of manufacturers. Do you think I can stay with a 6” balancer so I can keep the timing chain cover, or would a 6 3/4 be better. If I go with the 6 ľ or even an 8” since I have to replace what I have anyway, where do I get the timing chain cover that has the tab in the right place. Then to add to all of this, do I go with a press on, or since the nose of the crank is already threaded for a bold, one that is held on with the bold. I would like to go with the bolt type balancer but most of what I look at do not indicate if it is bold on. Then there is nodular iron, steel, and aluminum.

In Summit I just saw a couple of balancers that would fit under my current timing tab. One is the Pioneer Street Performance Balancers 872001 that is rated up to 6500 RPM, 6.12”. Another is the Professional Products Power Force Dampener that is 6” in diameter. No RPM rating though. Another is the Pioneer Race Balancer 872021 – 6.1”. There is a note, however, that says that “TDC mark is located 10 degrees from keyway. What the……………..does that mean as far as my application.

Way too may choices, way too many little differences that you need to know about how they would or would not fit my application, or what I would have to change……if I knew what to change.

I would appreciate recommendations as to what balancer. If it is bigger and 6” where to get the timing cover that would work with it and if and how to move the timing tab. Once I get this balance business worked out I can order it and the cam kit, and get the engine to the machine shop.
Thanks so much for your input. Mark

pop23235

I'll only attempt to address GM products as aftermarket is unlimited and very little data.
If you change from the stock 300 HP 6" balancer, you'll need an 8" balancer from a 327 SPHP application. This required a different timing cover and a large bolt and thick washer to install. It is good up to your 6500 RPM range by GM.

Randy G.

I just looked at all the harmonic balancers for sale on Summit's web site a few weeks ago and it gave me a headache. Some are pretty pricey. I figured the general got it right the first time so I ordered the GM Performance 8" for my 383 stroker that's going in my '62 and took my wife out to a nice dinner on the money I saved by not buying one of those fancy looking ones. The 283's in my other C1's all have the stock 6" what I call crank hubs.




.

rfn026

I've got an article coming out on harmonic balancers next month.

My advice is to stay with the GM OEM balancers. Maybe the GM performance items but avoid the others.

The dampers that use fluid have a problem with the fluid thickening and then becoming solid. A damper using fluid has to be replaced on a regular basis.

The ones that use rollers were designed for aircraft engines. They work great at a steady rpm. They're terrible though if you go up and down the rpm rpm range. Scat says 92% of the broken crankshafts come from this tip of damper being used in cars.

Here's an excerpt from the article.

"A few years back GM ran a series of test using a 427-cubic-inch small block. From 3,000 rpm to approximately 6,500 rpm all of the dampers tested limited crankshaft twist to no more than 0.6 degrees. Above 6,500 rpm things got interesting. At 7,800 rpm one damper allowed a rather considerable 2.0 degrees of crank twist. The second damper they tested allowed 1.7 degrees of twist, and the third had allowed 1.25 degrees of twist. And these were all brand new units."

Richard Newton
Car Tech Stuff

MikeM

Nobody wants to stick their neck out, eh?

In a street engine, the axle gear ratio has a lot to do with the required selection. That's assuming you're driving legally of course.

To the original poster. If your final drive is in the 3's and you're not going to be constantly ******* the engine, I go for the OEM replacement 327/300 balancer and not worry about it.

You've been advised in previous posts where to get an OEM balancer. No need to plow that ground again.

That is my opinion, based on opinion/experience not on engineering fact.

quahog

I'm in the process of getting a 6 in. balancer as we speak for a 67 327 with 300hp. Just got the engine rebuilt and the 6 3/4 in balancer I got with the car does not fit. 67's came with a 6 1/2 in balancer , the balancers key lines up with the timing mark on these balancers , newer balancers don't line up creating timing issues. Thru a post on ncrs I have found a replacement part # it's dayco pb1012n , in researching the availability of this I came across a powerbond balancer with the same # , more research and it seems the powerbond and dayco are probably the same part. The engine I have will probably produce @ 330 hp and I;m going with the dayco , it is a 6 in. balancer. hope this helps . Jeff

Mr D.

I'm curious, how long did it take to put 112K on the engine?