TheSamba.com :: View topic

Sun Jul 14, 2013 1:00 pm

I know what you meant.
Berg, FAT, and VW, did give up on using used engine cases, about 20? years ago
The "mystery" of why a used engine case would run hot, make less power, ect, is no mystery when the case is inspected in close detail.

At that time it wasn't practical to spend that amount of time and effort into fixing an old case when the new ones were very good and reasonably priced at that time. Much has changed in 20 years, now there is more than used and new, we got the good the bad the ugly, and the who knows what :lol:

Tue Jul 16, 2013 9:03 am

Machine work is machine work. Anyone can replicate any machining challenge if you have the equipments and know-how. Lineboring is no deep secret. Doing it properly is the big mystery.

Most linebore jobs have tendency to overheat coz friction by misalignment of the bore job on the mains. If the 4 mains do not line up, then some journals will load harder and produce heat and cook the bearings.

The alignment is dictated by the end bushings -feed unit and tail. So if the bushings are worn, that same tolerance will impart on the dimensions of the holes and alignment. The Porta-Tool unit is very much prone to this as the bits are held on bodies and secured by setscrew -WOBBLY!

The TruLine does not have this issue w/ holding the bits. Also has the bigger bar as rigid as you can put in the case tunnel. Leadscrew feed is always positive feeding.

I do not have issues w/ larger main bearings. Most high-end cranks have 411 mains now. That is way larger than 0.080 size!! The key is to do the linebore correctly.

Tue Jul 16, 2013 12:22 pm

Why would a line bore affect oil pressure?

And just as a side note. It is what people have wrote, spoke or just plain muttered in error that creates most VW BS in the first place.

Tue Jul 16, 2013 1:41 pm

Oil pressure is a function of total clearances...lifter bores, rod side clearances, bearing clearances to journals, function of oil plungers, oil pump size.

The linebore should not have anything to do w/ oil pressure. Not really sure why anyone will think that.

Wed Jul 17, 2013 5:43 am

So you guys are saying that if I have a crappy line bore job and it's "egg shaped" or the bore is too large and it lets oil "leak" out past the bearing surface that won't affect oil pressure at all?

Wed Jul 17, 2013 9:03 am

The bores cannot be out of spec or you will NOT have bearing crush. PERIOD. There is so little mistake allowed....few thou so the tool had better do a good job the first time.

And each oversize bearings have to maintain stock clearances. You don't set that clearance, the factory did that. I have never had to extra clearance the ID of a bearing to accomodate the crank journals.

For undersized bearings ID, if the crank grinder follows the specs of a re-grind then all is well when you buy undersized bearings.

The only thing we lineborers manipulate is the bearing crush, out of round, bore finish. If you do these right -all within, there is nothing here that will affect oil pressure.

Wed Jul 17, 2013 9:25 am

Its very hard to do an out of round/eggshapped line bore. It is possible but you really got to be trying to mess it up to do it.
The whole purpose of the tools, either portable or stationary is to cut a straight bore. Using the portable line bores available to most it is almost impossible to get it crooked if it wasent crooked before. I say almost because you cad do it if you really want to. The main issue with the line bores is surface finish or over or undersized bores due to worn cutting tools or someone messing with the radius.

Wed Jul 17, 2013 9:57 am

^^^ yup, but it can be done by some type of"exsperts".

Wed Jul 17, 2013 12:11 pm

The tunnel can end up w/ tapering if the small bushing is loose. And quite possibly out-of-round. The bar will "wiggle" at the loose end and not at the tighter end. So there will be tapering on the mains.

These anomalies will not be there if the bushings are all within tight tolerances. I like slide-fit bushings. The bar will forward smooth and cutters will do their best if keen and proper radius.

It is all in the nature of the tool how well it is taken care of. Good tools will always give good results.

Sat Sep 14, 2013 6:25 am

In align boring my own old cases, here's what I've noticed:
The case half parting lines are no longer a flat plane as it was when initially manufactured. This can cause machining errors when cutting cylinder spigots that we would like to be perpendicular to the main bearing centerline.

Resurfacing the case parting line to re-establish correct flatness is time and labor intensive and may alter the cranks distributor gear to drive fit too much.

The front seal bore (flywheel end) that the align bore tool registers in is not necessarily concentric to the centerline of the original main bearing bore when the case is manufactured. Its not an issue until the seal bore is used as a registration point for re-machining the main tunnel. By using it (the front seal bore) as a register for locating the align boring tool, the main bearing bore may be shifted out of perpendicularity to the other machined surface geometry ( cylinder spigots) and cause the pistons and rods to be in a slight non-perpendicular relationship to the cylinders which were machined relative to the case parting line, causing a bit of overheating from increased friction And less than ideal oil flow around the bearing journals.

All these can be addressed by conscientious machinists taking unconventional extra steps...removing case studs and lapping case halves flat prior to machining, or doing spigot machining in a special fixture that registers off the new align bored main tunnel if the tunnel is no longer perpendicular to existing case geometry , but it does take much time and effort...which costs money. When cases were cheap, it certainly wasn't worth it. I feel perhaps gene berg became aware of these issues plus the other possible issues like fatigue and worn lifter bores, and realized it was more efficient to buy a new case than correct all the issues that exist in an old case. Perhaps now it is worth it...to the conscientious consumer.

The devil is always in the details and some consumers chose to ignore the non-obvious issues and hope for the best, but they are likely to be the ones to be disappointed later, especially in a high performance application, unless they are fortunate enough to have a case with good geometry to begin with. In that case it's really just luck, as the geometry is rarely checked when align boring takes place.
Ken

Sat Sep 14, 2013 6:57 am

Does the case need align boring?

A Vw case is soft and squashes it's self around the main bearings. You will be able to see a channel that the oil grove on the back of the main bearing has made in the case. The thrust bearing will wiggle if you just have that installed between the case halves with the crank removed. If the end play is extreme and was set correctly once , the thrust bearing saddle needs to be oversized. I don't see this explanation spelled out so I wanted to post it. I'm thinking that the more the end play, the more energy is created to mush the thrust bearing saddle. I had a badly damaged crank in a jeep which never effected the thrust bearing so some thrust bearing crankshaft designs are not prone to consequences from a beat thrust bearing. :shock: