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36hp Line Bore / Bearing Crush - Dims.
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Mr. Okrasa Premium Member
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PostPosted: Wed Jan 20, 2016 11:44 am    Post subject: 36hp Line Bore / Bearing Crush - Dims. Reply with quote

I'm setting up my (4) Tru Line boring bars for 25hp-36hp engines and reading online "different" case bore dimensions? When I check the measurement on
the actual bearing(s) O.D. vs. the "recommended" case bore dims., either the crush is not enough or sometimes way out there!?!?

Any recommendations as to what bearing crush is "good" based on prior experiences? Cheers! Mr. Okrasa Cool
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Mr. Okrasa Premium Member
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PostPosted: Sun Jan 24, 2016 11:44 pm    Post subject: Re: 36hp Line Bore / Bearing Crush - Dims. Reply with quote

Mr. Okrasa wrote:
I'm setting up my (4) Tru Line boring bars for 25hp-36hp engines and reading online "different" case bore dimensions? When I check the measurement on
the actual bearing(s) O.D. vs. the "recommended" case bore dims., either the crush is not enough or sometimes way out there!?!?

Any recommendations as to what bearing crush is "good" based on prior experiences? Cheers! Mr. Okrasa Cool


Anybody???
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PostPosted: Mon Jan 25, 2016 10:33 am    Post subject: Re: 36hp Line Bore / Bearing Crush - Dims. Reply with quote

As the crickets chirp.......

.001" to .002" on bearing crush is what is needed, however giving an exact dimension is difficult given the main bearings that are available today for 25/36hp vary in OD by brand. There are Repco, KS, Glyco, Metal Leve, some plain white box which are also Metal Leve and the Sintermetal Aregentena bearings (red box). Not to mention the factory VW sets that may be on a hoarders shelf somewhere. Setting the cutters is pretty much an engine by engine type of deal for early engines anymore.
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PostPosted: Mon Jan 25, 2016 12:02 pm    Post subject: Re: 36hp Line Bore / Bearing Crush - Dims. Reply with quote

Hi Matt,

Its hard to set-up the boring bars based on printed matter on the net. When bearings are measured, the sizes vary
from different manufactures so its difficult at best to try and set them up for "one size fits all" type of scenario.
My understanding is .0025 is a "good" crush but maybe that is a bit too much? Thanks for your help. Joe

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1950 Split Window 356 Coupe / Adria Blue Metallic
1951 Split Window 356 Coupe / Radium Green Metallic
1952 Split Window 356 Cabriolet / Azure Blue
1959 VW Karmann Ghia Coupe / Bamboo-Green / Denzel 1300cc / OG. owner, paint Wink
See this link: https://vimeo.com/139432553

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TomSimon
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PostPosted: Fri Feb 05, 2016 1:01 pm    Post subject: Re: 36hp Line Bore / Bearing Crush - Dims. Reply with quote

My experience has been setting up a T1 race crankshaft, that was made specifically with all 3 mains T4 diameter, for strength.

Not to be confused with the T4 center main, where you can just use an 'adapter" bearing in the centermain location (which turns out is just a BMW rod bearing, but that's another story) Rather, Scat made (still makes?) semi-custom T1 race cranks with all three large mains T4 diameter, a T1 nose bearing, and a flanged T1 rear main. A bit of a Frankenstein's monster, but as you guys know in the race parts world, anything goes!

Anyhow, that process includes having the T1 case tunnel bored to accommodate the larger (in both ID and OD) T4 main bearings. This took a couple tries to get it right, as the crush was off the first time around. As a result, I got a first rate education in having to sort it all out.

Like Matt says, it's kind of a crap shoot, no 'onesize fits all' but what I discovered is about .001" crush worked out well.

My crank was tight, would hardly spin in the bearings. I pulled it apart, removed the main bearings and crank, and re-torqued the 6 big nuts.

I used my dial bore gauge to perform a full on inspection of the mains, this time with no crank, only the bearings only installed. One was indeed tight, one bore was smaller than the crank's main journal. To find out if it was a bad bearing or mis-machined case, I needed 1 more set of measurements.

I pulled all the bearings and measured the bare case bores. Sure enough, one T4 diameter saddle, the one closest to the nose,was align bored undersize. measuring the 3 main saddle diameters, three places around the diameters as well as fore and aft in each saddle, writing everything down.

The holes were reasonably round and non-tapered, but one was small. Mind you this location takes a full circle bearing, and the nominal .0025" clearance was so squeezing the crank, it would hardly turn unless I loosened the 6 big case nuts! The machine shop fornicated the canine on that one...

What I found is this: The full circle bearing wasn't damaged, it sprung right back when ever I loosened the case nuts, which made the problem a little tough to isolate. Anything more than about .001" crush, closed up the bearing bore, giving less room for the final bearing to crank journal desire clearance. I also found there's no magic to it. Having your own boring bar Joe, puts you in the driver's seat. You get to set the case tunnel to suite your box of bearings!

What I'd do is measure the 1 full circle bearing out of the box, cut the tunnel with .001" crush. Install the bearings, measure with a dial bore gauge, do the math. The final test is install the crank with bearings and a few drops of oil, and give it a spin.
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PostPosted: Sun Sep 25, 2016 5:50 am    Post subject: Re: 36hp Line Bore / Bearing Crush - Dims. Reply with quote

Just found this thread. If I may input my limited experience w/ lineboring VW engines....

Nice micrometer tool there, Joe. Looks a lot like mine. Laughing

Lineboring is not new. Goes way back to the first engine. But the technique has not changed much.

To cut a straight and round hole along an axis, you have to have a very good end support bearing on each end of the bar. This is of the outmost importance -as you can imagine you cannot machine a round hole if the end supports are wobbly. YOu will just end up w/ an egg-ed shape hole.

So by the time you 'crush' the bearings in place, the egg-shaped hole will pinch the shaft. So your tendency is the bore the mains bigger and loose the 'crush' to loosen the bearings. But this is wrong! If you loose the bearing crush, then the bearing will spin in the mains.

How much crush is required? Well, depends on how big the bearings are. If you are pressing a small diameter bearing like a valve guide, 0.0005" interference is plenty. But on the other hand, if the bearing is 3 inches DIA across x 3/4" depth, you will need more than that.

When you bore the mains, like in a Type IV centers, you cannot cut that thing in one swipe. Which is what I am thinking people are doing. There has to be several roughing passes before the final sizing cut. I like to setup the final sizing bar to only take out 0.005 - 0.010" on its final pass.

You can set up a bar to do the roughing passes w/ dedicated micrometer tools w/ increasing cut/thickness to setup the bits. It need not be exact as it is roughing passes after all.

On the final pass, you have to creep up on the bits' stickout to get to the final pass. Yes, it is a lot of work to setup and cut this way but it is the most accurate.

I am working on a boring bar project I have had in my mind since I started doing linebore work. My best solution is to use microbore toolings. This is a very expensive proposition to use in this process. Otherwise, we are relegated to use the above process.

And one more detail in boring to Type IV mains, DO NOT USE the nose of the case to attach the end support. The best way is to machine a dedicated bushing that will locate in the #4 main saddle. Obviously, the reason for this is to align the rest of the mains to the #4 bearing hole.

There, I have given up all my lineboring pearls. Do I get a cookie? Very Happy
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PostPosted: Sun Sep 25, 2016 5:53 am    Post subject: Re: 36hp Line Bore / Bearing Crush - Dims. Reply with quote

Also, follow the factory size dimensions or tolerances for the size bearings you will be using. It is a range from tight - loose. I like the middle.

That is what she says anyway. Laughing
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PostPosted: Sun Sep 25, 2016 4:41 pm    Post subject: Re: 36hp Line Bore / Bearing Crush - Dims. Reply with quote

Joe, I like .0025 to just under .0015. Anything less causes me to worry.
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PostPosted: Tue Nov 01, 2016 10:22 am    Post subject: Re: 36hp Line Bore / Bearing Crush - Dims. Reply with quote

nsracing wrote:

When you bore the mains, like in a Type IV centers, you cannot cut that thing in one swipe. Which is what I am thinking people are doing. There has to
be several roughing passes before the final sizing cut. I like to setup the final sizing bar to only take out 0.005 - 0.010" on its final pass.


In referring to the top quote by NSRACING, I'm talking about line boring 25hp/36hp blocks and not type IV. When removing material when line boring say
from STD to .020", were assuming we are taking out less material than .020" since the block is worn. Knowing that, the cutter is removing .010"
per surface so doesn't that equal .020" which is what we are going for and less than .020" per pass? Rolling Eyes

Thoughts?
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PostPosted: Thu Jun 22, 2017 11:33 pm    Post subject: Re: 36hp Line Bore / Bearing Crush - Dims. Reply with quote

Well, the cut will be that much on each cheek so to speak. About 0.010" per side.

But you set the bits on what bearings you like to use. So measure the bearings and set the bits so you have your final pass and bearing crush.

It is tricky to come up to the final pass and have set the toolbits to final dimensions. Gotta have a way to measure the final bores and figure out total measurements. i.e. how round the bores are. A nice dialbore gauge is needed.
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PostPosted: Thu Aug 03, 2017 10:18 am    Post subject: Re: 36hp Line Bore / Bearing Crush - Dims. Reply with quote

Thought I would share my new tool. Since I made up the Tru Line style line boring bars because the later 40hp - 1600cc wouldn't work because the bars are obviously longer and the cutters in the wrong location for 36hp, I had another dilemma. The thrust cutter? The flywheel seal area where the Tru Line tool indexes from for the later engines is larger thus wouldn't work on the 36hp/356 blocks. If I had a 36hp block that needed it's thrust cut, I would line bore it first and then would need to take it over to my machinest and have him cut the thrust for me. This is fine but when he's about 2 hrs away round trip, that's too much time driving so.......I made up this thrust cutter. It attaches via the locating studs/holes where you bolt it to the transmission. I've used it a couple of times and so far, no worries. Whats great about it is you can use it for the later blocks as the cutter is adjustable! Cheers!

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1950 Split Window 356 Coupe / Black / #500X
1950 Split Window 356 Coupe / Adria Blue Metallic
1951 Split Window 356 Coupe / Radium Green Metallic
1952 Split Window 356 Cabriolet / Azure Blue
1959 VW Karmann Ghia Coupe / Bamboo-Green / Denzel 1300cc / OG. owner, paint Wink
See this link: https://vimeo.com/139432553

VW www.Okrasa.com
356 www.PreA356.com


Last edited by Mr. Okrasa on Thu Aug 03, 2017 4:39 pm; edited 1 time in total
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PostPosted: Thu Aug 03, 2017 2:20 pm    Post subject: Re: 36hp Line Bore / Bearing Crush - Dims. Reply with quote

That is an idea -

My only issue w/ this tool is alignment and perpendicularity. Since this tool will locate from the outside, establishing a square 'tilt' is at issue. If you do the cut on the thrust, did you mic the thickness of the thrust to be all even or close to even? If one cheek is not the same thickness as the other or has a taper, then the tool is not square to the thrust.

The beauty of the TruLine thrust cutter design is that you will locate from the back of the thrust and it is nicely machined flat already. The cutter body will home in from the back and bottom out and then held in there by a lock. So the cutter -coming in from the other side- will always follow that straight and you end up w/ an even thrust for the bearing.

Your design is basically like a milling machine head. Imagine the thrust as the mill table. And the cutter head/body is the milling head - which has to be trammed to be square w/ the table. Otherwise, you will not produce an even cut. It will be tilted - thick on one side and shallow on the other.

If the thrust surface happened to be even, then keep the tool same way mounted each time and keep however many shims it takes to prop the legs from the case bolts.

Nice tool.
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PostPosted: Thu Aug 03, 2017 3:17 pm    Post subject: Re: 36hp Line Bore / Bearing Crush - Dims. Reply with quote

Hi Nick,

That was also my concern about perpendicularity. The surface that the tool sits on is a hard location also. Nothing wears or gets out of round or ???
I have done several and mic'd the thrust surfaces and there are no variances in measurements so everything checks out. Cheers.
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1952 Split Window 356 Cabriolet / Azure Blue
1959 VW Karmann Ghia Coupe / Bamboo-Green / Denzel 1300cc / OG. owner, paint Wink
See this link: https://vimeo.com/139432553

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