Diesel Crank In Mi16 Iron Block

[Mad Scientist 106]

At the moment I am going down the road of installing a XU11d crank into an S16/Mi16 iron block.

 

I have spent quite a bit of time talking to the guy who will be balancing the bottom end today and it has thrown up some queries.

 

With regard to lightening the crank, is this something that others have done? I have weighed the S16 crank and the XU11d crank and they weigh just about the same as standard. The worry comes from the diesel crank only having 4 counterweights as apose to the S16 crank having 8. This can be seen in Dr Sarty's project thread in the picture here: http://forum.205gtidrivers.com/index.php?s...74000&st=20 (thanks for that Rich).

Our worry is that the diesel crank is only designed to opperate at lower revs, and thus has been weighted to do so. Are the 4 weights sufficient to keep the crank running at higher revs without issue over time? We think that removing MORE weight would only make the problem worse.

 

I'm now thinking that just a careful balance may be more appropriate. If I want to save some rotating weight, perhaps a lightened flywheel and pulley would be more appropriate/safer.

 

I know Dr S has c. 8000 miles under his engines belt, but I am not sure what was done with his crank..................or whether he wants to share that information.

 

I'd appreciate some input here from those that have built and run these conversions.

 

Thanks,

 

Pete

[M_R_205 5 1 Cars]

I noticed and was thinking exactly the same thing last night while trying to find a diesel crank... I think if there were any problems with revving the diesel crank it would have been thrown up (literally) in Sartys car, from what i can gather i believe hes rev limit is around 8000-8500?

 

Paul.

[Batfink 201]

With the longer stroke you are creating a more lazy engine anyway so I think as long as its well balanced it should not be a problem..

Its sustained high rpm that will be the risk

Edited April 27, 2010 by Batfink

[dcc 855]

I remember reading somewhere about a 11k rpm race engine with an 8v crank fitted (4 counter weights) so I personally wouldnt be too worried about the weights.

[Silky 33 1 Cars]

I have a 1.9 DT engine sitting in my garage from a 306, took it out a couple of years back and the engine has sat in my garage ever since.

 

Am sure the crank is still in there, is available free of charge to anyone who wanted to collect it, don't know if this is the type of crank you guys are talking about

[Batfink 201]

I remember reading somewhere about a 11k rpm race engine with an 8v crank fitted (4 counter weights) so I personally wouldnt be too worried about the weights.

 

find out more! sounds wicked

[weejimmy 1]

the t16 crank is only 4 couhnter weights too and they rev higher than a td ok.

[GilesW 41]

My brain is struggling to understand what is the percieved differance between 4 or 8 counterweights?

 

? - some 'twist' stain on the crank?

 

Surely the counterweights are there to balance/smooth rotation against the rod/piston mass, so 4 would be as good as 8 so long as the mass was right.

 

Saying that I always thought that balancing the mass was more important than the weight matchin that it is expected to balance - ie balance so minimal vibration; but due to the balanced nature of teh 4 piston layout on the crank the physical weight of teh balanced crank had little effect on balancing the crank against it's rod/piston weight.

 

Indeed - very revvy race engine have very light cranks with no counter weights don't they? Yes they may vibrate more, and yes they might need more regular servicing (but that type of engine would for many reasons anyway) - so are we really focussing on the wrong thing, ie 4 or 8 weights are not a factor. Far better to find the lightest crank possible and get it properly balanced?

[Mad Scientist 106]

I guess one of the big factors to this is that I want to put together a reliable road car, that can drive to Germany and back without issues.

 

The 4 or 8 weights is not strictly a factor, but the 4 weights on the diesel crank were designed to compensate for the diesel rods and pistons which were HEAVY. I initially thought that quite a lot would have to come off them to balance up with the S16 rods and forged pistons. This is something I won't know until it goes to the balancing shop. I've looked at some of Dr Sartys other pics in his thread, namely the ones QEP took when assembling the engine, and it doesn't look lightened to me. I guess i'll have to wait for my pistons to arrive, then take it for balancing and see what they say.

 

I don't intend to rev the nuts out of this engine anyway. In fact, I expect 7500rpm to be the max, and only revving that far sometimes.

[sub205 5]

the additional 4 weights are mainly for a smooth run... the newer engines have to run smoother because the customers dont want rough idling and so on ... :-p

 

i converted from XU9JAZ to XU10J2 one year ago, its amazing how smooth the idle is, nearly no engine vibration while waiting for the lights to turn green.

[DrSarty 90 1 Cars]

Sorry to reply late.

 

QEP (well Nick specifically) did not do any crank lightening as far as I'm aware.

 

My engine will rev quite happily to over 7k, and there are no un-toward vibrations at any RPM; in fact I would say it's very smooth. As Anthony said: 'it pulls like a V6'.

 

My bottom end is balanced all the way through, i.e. rods match-weighted with pistons which are balanced to a balanced crank, which is finally balanced to the flywheel. But I thought this was standard practice anyway regardless as to how many counterweights the crank has.

 

So all told I don't think you have anything to worry about, and I believe the diesel crank's material/treatment makes it a tougher crank anyway.

[24seven 104]

My brain is struggling to understand what is the percieved differance between 4 or 8 counterweights?

 

? - some 'twist' stain on the crank?

 

Surely the counterweights are there to balance/smooth rotation against the rod/piston mass, so 4 would be as good as 8 so long as the mass was right.

 

Saying that I always thought that balancing the mass was more important than the weight matchin that it is expected to balance - ie balance so minimal vibration; but due to the balanced nature of teh 4 piston layout on the crank the physical weight of teh balanced crank had little effect on balancing the crank against it's rod/piston weight.

 

Indeed - very revvy race engine have very light cranks with no counter weights don't they? Yes they may vibrate more, and yes they might need more regular servicing (but that type of engine would for many reasons anyway) - so are we really focussing on the wrong thing, ie 4 or 8 weights are not a factor. Far better to find the lightest crank possible and get it properly balanced?

 

 

If you look at the picture of the crank with only 4 counterweights, imagine laterally along the shaft where the weight of the crank pin needs balancing to. Ideally you'd have an identical shape/size crank pin extending out 180degrees from each existing crank pin to balance them, but obviously this wouldn't work. Having one single balance weight off to the side is still better than having nothing, but it creates another twist in the shaft by being offset. If you have 2 counterweights per crank pin both evenly offset either side of it, you can balance it without inducing this other twist and so you're not putting an extra force into the bearings which can wear out quicker.

 

On a diesel engine, this isn't such a problem because of the low RPM. Same story on the 8v's with their sub 7k limit from the factory (6800? It's been too long since I've owned an 8v) Peugeot didn't think 8 counterweights were necessary so they only use 4 I assume, but on the 16v engines someone somewhere must have crunched a few numbers and decided 8 weights way the way to go.

[brumster 135 1 Cars]

I've mentioned this recently in another thread. The recommendation from Longman when I was chatting with their engine builder once was that for sustained high revs (say track race work) they'd look to use an 8-web design crank, but for the stage rally engines they were building for myself and Andy, they have used 4-web cranks with good success. But these engines are regularly stripped down and checked anyway, and I know Andy Baker has got through a few bottom ends over the years, but I'm not saying that's conclusively proof that the 4-web design is a bad idea (his 8v crank was reduced down to nothing anyway!). It makes for a very light, snappy, revvy engine.

 

Unless you're planning on bouncing it off the 8k+ rev limiter for minutes at a time and expecting a 60,000 mile rebuild interval, you're probably safe

[Henry Yorke 269 3 Cars]

As has been said, balancing is mostly there to stop it shaking itself apart at higher revs and aide smoother running. The balancing impacts the centrifugal force applied to the crank. The 2.0 Alfa TSpark 16V engines had twin balancer shafts, though this was not on the 1.8 version. This was due to heavier pistons etc being thrown about in the engine in larger capacity engines.

More info here: http://www.autozine.org/technical_school/engine/smooth2.htm

 

The diesel cranks will have been designed for lower revs and it will be more cost effective in the manufacturing process to balance one counterweight as opposed to 2. They may be made of stronger material to deal with the turbo torque though.

 

The Porsche 944 had a 3 litre 4 pot engine so it may be worth looking at one of those as a reference. The sheer nature of a 5, 6, 8 or 12 cylinder gives more balancing options as there are more sticky out bits on the crank to adjust.

 

The Longman 240bhp 8v I knew of had a custom (billet?) crank, but I don't know any more on the spec of that.

 

Would a hi revving not perfectly balanced crank just cause premature bearing wear and therefore early failure or would just be a sudden catastrophic event? Obviously a regular rebuild would address the former, but the later is less predictable

[brumster 135 1 Cars]

The Longman 240bhp 8v I knew of had a custom (billet?) crank, but I don't know any more on the spec of that.

 

Aye, so probably a lot stiffer and hence flex not something to worry about. But all 4-pots are inherently unbalanced, if that's the word, hence balancer shafts like you mentioned above - you're clued up on that already, I suspect

 

Would a hi revving not perfectly balanced crank just cause premature bearing wear and therefore early failure or would just be a sudden catastrophic event? Obviously a regular rebuild would address the former, but the later is less predictable

 

My understanding is the former; you'll see uneven bearing wear first. So plenty of warning if you're stripping your engine regularly, which is what most of the highly tuned race engines would be doing anyway?

[Mad Scientist 106]

Some interesting reading there. Thanks. I need to weigh up the balance (pardon the pun!) of longeivity versus engine spec. I don't really want to be pulling this apart very often...............or ever even!

[wracing 19]

correct me if im wrong, but what about a td crank 8 balancing wieghts and forged i think!

 

James

[Mad Scientist 106]

The crank i'm using is from a 2.1td 406.

[wracing 19]

haha, sorry misread

[petert 588]

I think it's more to do with the manufacturing process rather than anything else. Diesel and T16 cranks are forged, whereas others are cast. It's relatively easy to add the extra counterweights to a casting, but not a forging.

[B1ack_Mi16 67]

I've been revving the 2.1 TD one to 8000rpm for some time and it seem to be fine.

 

I've even increased the stroke to 94.5mm and hence using smaller bearings...

[Batfink 201]

if you are using custom rods and pistons they are going to be inherently lighter than the originals so there will be reduced forces at play.

[Tom Fenton 1,542]

The Porsche 944 had a 3 litre 4 pot engine so it may be worth looking at one of those as a reference.

 

2.5 litre, and has a balancer shaft.

[Anthony 1,003]

2.5 litre, and has a balancer shaft.

944 S2 was 3.0 litre

[24seven 104]

It came with 2.5, 2.7 and 3.0 straight 4's all with 2 balance shafts.

 

If the diesel cranks are forged, surely the extra strength over being cast will to some extent negate any reliability woes due to it being less balanced?

Edited April 29, 2010 by 24seven