Another Duratec question - does the bottom end need balancing?

[Shaun_E]

I am in the process of replacing my K with a Duratec (target 263bhp). It will have steel rods and forged pistons but a standard crankshaft. It will have a rev limit of 8500ish. The question is: should I have the bottom end balanced?

I've had the bottom end balanced on both my previous K series engines but it has been said that the Duratec doesn't need this done.

[Paul Deslandes]

not sure about balancing but you should get the cam chain gear keyed to the crank. Standard is friction washers apparently.

[elie boone]

It's always good practice to balance, and while you are at it balance the lot, crank,flywheel and clutch cover.

[Pendennis]

Not necessary, would be a waste of money.

 

Keying the crank in the long run is well worth the money, if crank has already been used get it crack tested, but if new don't bother

[Shaun_E]

Thanks folks. Yes the crank, pulley and gear are being keyed and a heavy duty chain tensioner will be used.

[Pendennis]

The standard chain tensioner is modified to prevent it and the chain from bouncing during high rpm, from memory approximately 6mm section of an old valve guide is all that is required

 

Edited by - Pendennis on 5 Nov 2012 16:12:08

[AMMO]

I haven't built an engine in the last 30 years that hasn't been dynamically balanced. In the case of the Duratec the cranks from Ford are very good as standard. They require little or no work. Once you start adding the pulley, flywheel and clutch cover is when balancing become necessary. I demonstrated this on a balancing machine at a Duratec clinic I did years ago. In fact rather than talk about balancing the crank we should be looking at the crank assembly as a whole.

 

I year or so ago I re-built an R500 engine where the crank assembly had not been balanced from new. I keyed the crank and balanced the assembly as a matter of course. The customer commented that it was much smoother after the re-build.

 

The chain guide is something that I started modifying years ago after problems with the standard ratcheting tensioner over-tensioning. I think Rob Grigsby was one of the first people to encounter this problem. From memory the engine lost power and deveIoped a very bad vibration. The chain was incredibly taught. I think I explained exactly what happens elsewhere on this forum years ago. If you do a search you may find it.

 

To resolve the problem I calculated the expansion of the block and chain and worked out how slack it needed to be when it was cold to give the correct tension when the engine was up to temperature. We checked this on the dyno when the engine was hot and the calculations were spot on. The amount of tension when hot was perfect. You have to get it right as re-tensioning the chain involves taking the timing cover off.

 

I make the tensioner adjustable as it is better to use a lightly worn chain rather than a new one. The new one will wear very quickly early in operation and would result in a slack chain in no time. Within a thousand miles. You cannot just make a spacer of a fixed length because the block or head may have been skimmed for squish or compression. Also being adjustable means that you can re-tension it quite easily in the future during a re-build.

 

Hope this helps.

[Rob Walker]

Nobody keys the cranks anymore its not necessary, and hinders the valve timing process as nobody uses the vernier cam chain sprockets.

 

I would not bother balancing the crank as Ford seem to do a very good job. I would check the individual weights of both the rods and pistons some of the recent ones that I have bought have been as much as 1.5 grams out. By far the most important area for the attention of the balancer is the flywheel and clutch assembly.

 

The cam chain tensioner is modded by removing the hydraulic plunger and discard the spring and ratchet pawl then tapping the hole to take a 6mm cap allen and k locknut the plunger can then be set to the fixed desired tension.

 

Rob

[Pendennis]

I keyed my crank and it did not hinder the timing, in fact I think it made it easier because I could do it comfortably without the timing cover being on. Rob, I had the front crank pulley oil seal fail during a race meeting on 20th October, the problem was I needed to be at the Birkett on the 27th October. I managed to change the seal, stress free in 40 minutes because I had keyed the crank, I can't see it being that easy if the crank wasn't keyed. I'd like to add the key is good tight fit, thus no slop.

 

I also considered balancing the whole bottom end as mentioned above, but could not convince myself it was money well spent, how could I be certain the clutch plate cover would be in the exact position during assembly. And, after 8-9 years of racing a Duratec, during which I have probably fitted 4 clutches, each time I slapped it on and aligned the plate, never had an issue, just like your Mondeo won't went it leaves Ford after a new clutch

 

Ian

 

 

 

 

Edited by - Pendennis on 5 Nov 2012 18:46:00

[7 wonders of the world]

The balancers usually mark the flywheel and cover with 1/4 so you can aligh them in the same orientation during final engine build.

[Pendennis]

yer, but do we presume the clutch plate is symmetrically balanced then and what happens when you need to install a new clutch assembly

 

Like Rob's idea of weighing rods and pistons, wish I thought of that 😶‍🌫️

[7 wonders of the world]

Understand your point on the plate however most of the mass is nearer the centre so any inbalance will have less effect.

 

Most (but not all) balancers will have a 'slave' we used to have a crank / flywheel balanced to zero so we could balance new covers on this for customers this assumes the rotating itmes are individually balanced and not done as a total assembly.

 

ie balance bare crank, add sprocket/front pulley, add flywheel, add clutch cover.

 

Rod and pistons should always be checked, recently replaced 1 piston from a well known maker only to find it was 4.8g heavier than the others 😳

 

Most rod sets are supplied within 1g now

[Rob Walker]

Pendennis,

My post about not keywaying hindering timing can be misunderstood and needs explaining in that it allows the builder to follow the ford timing method which is the way you have to go if you also go without the heavy vernier cam sprockets in favour standard oe sprockets and cosworth diamond washers. The idea is to reduce the rotation mass of the valve gear and also save money. I am aware that keywaying does have its advantages but wanted to post that most current duratec engine builders no longer keyway the crank. I personally like the keyed cranks.

 

When balancing I have found the biggest balancing issues have been with the flywheels the worst being 27grams out. In recent years AP whoes clutches I use have gone to some effort to balance both their clutch covers and friction plates, this certainly was not the case when we used their clutches back in the 90s on the K series engines. Imo balncing a crankshaft down to 0.1gram is just not necessary on Duratec that is reving less than 9000rpm.

 

Rob

[Pendennis]

no worries Rob.

 

 

[elie boone]

The Mahle forged pistons i bought 20 years ago also had a weight differnce of about 1,5gr it seems the industrie standaard

But 1,5 gr is a big shunck out of the piston, lucky i have scales to 0,1gr at work that i can use

Rods are more difficult to measure on both sides but forged one's seem to be pretty near equal

[Rob Walker]

For rods and pistons you can buy small drug dealer scales off ebay they are accurate enough for this job + - 0.1gram cost about £20.

 

As regards removing material I took a trip up to Steve Smith (Vibration Free fame) and made carefull note of where he removed material. On the pistons he took material out of the taper on the gudeon pins with a die grinder and on the rods off the sides where the rod bolts enter with an angle grinder. Easy pezzy I was gutted when i got his bill for the full balance £250 plus vat. I now do my own static balancing .

 

Rob money saving expert.

[AMMO]

I've been thinking about cranks a lot lately so I thought I would add some comments to this thread.

 

My personal opinion is to always balance. My way of engine building is to do the best job possible and to build engines for customers as if they were for myself. When I get to a point that I have to decide what to do on an engine I ask myself what would I do if it was my engine that was going in my car. I don't want my engines to vibrate. It is bad for the engine to have the flywheel and / or clutch cover out of balance. Crank balance is not something to save money on. No point in balancing the pistons to 0.01 of a gram if the flywheel is 10 grams out of balance. The only way to find this out is to put the crank assembly on a machine and check it.

 

The vibration periods tend to be around 4,000 and 8,000. So for an engine that revs to 8,500 it would be pretty essential in my opinion. Especially if you are going to use the engine at that rpm at a regular basis in racing or on a track. Touring cars are limited to 8,500rpm. Do you think that the people that build these engines don't balance their cranks?

 

Getting a crank assembly balanced is a pain in the neck if you have to drive miles to drop it off and again to pick it up, or if you have to parcel everything up and send it buy courier. I can understand that for a road car you might want to give it a miss. After all there is a good chance you can get away with it. I'm in a very fortunate position that an ex-employee and friend has a balancing machine 10 minutes up the road and can balance an assembly while I wait if neccessary. So for me it is not a problem. I also get the cranks crack tested on the Magnaflux machine and the journals micro polished at the same time. That goes to explain why my engines have always been that little bit more expensive than other people's. I just put more work and expense into them.

 

It is also not true that nobody uses the vernier sprockets on the cams anymore. I had to order some of my own profile cams for two customers with race engines in Italy recently. Whilst I was on the 'phone I asked how many cams are sold with sprockets and how many without so they can be used with the original factory sprocket. The answer was that they sell ten times as many with the vernier sprockets as against the ones without. I have built 210 bhp entry level engines with the standard sprocket, but anything more expensive I always fit the vernier sprockets.

 

Apart from ease of cam timing there is also another reason for using the cams with the sprockets. If anyone can guess what it is I will donate £10.00 to NTL.

 

 

[oilyhands]

I always balance unless instructured not to.

 

Oily

[Golf Juliet Tango]

I'm not an engine builder, so feel free to discount my opinion but (as a buyer) I would suggest that the question is not "does the bottom end need balancing?" but "Is there any reason not to balance the assembly?". It certainly won't make things worse. Considering the cost of the whole engine, the added cost for some peace of mind strikes me as sensible.

[Birkin S3 ZA.]

I always balance my bottom end, when you pay attention to detail on all the work you do to a motor. it all adds up when you can gain very small amounts, just a small percentage makes a diffrence when it's 250hp.

It also gets Nitrided as well after shot peened, then crank balanced then + front pully then + flywheel then + clutch plate. Sounds 🙆🏻 but thats how some of us are 😬

My Duratec is stripped and will undergo all the pain and cost, I only want to do it once.

Chris

 

Edited by - Birkin S3 ZA. on 2 Feb 2013 19:13:02