lifter bore fixture bbc

[gnicholson]

i was wondering if someone could tell me if the typical bhj lifter bore location fixture locates off the cam tunnel or another point of the block? if it does not locate off the cam tunnel and it was off from the factory seems to me by using the fixture and machining it you would create a problem with the cam to lifter alignment. in other words should the cam tunnel and lifter operation be done together or not at all? is this something that should be done on a typical production block ? i.e. is it worth the cost?

[xenginebuilder]

The fixture has a mandrel through the mains and the cam tunnel. If the cam tunnel is not right, you can't get the fixture end plates to assemble correctly, but I never encountered that particular problem.
Is it worth doing? Absolutely. In my experience the BBC stock machining on the lifter bores is some of the worst for location and angle.
For example, another shop (doing mostly stock type rebuilds) in my area invested in a BHJ fixture for their BBC rebuilds, and they were still using a block mounted boring bar to do their cylinder bore work. They told me that it eliminated comebacks due to lifter/cam failures, so I guess it was worth it to them...

[gnicholson]

thanks. probably a dumb question. how else would it locate

[ALKYAL]

Have had this type BHJ since 1988. Have not found one pass/hi perf pass/or bow-tie from the factory that the cam tunnel and the crank C/L were in-line ether in vert or horz planes. To correct this the cam tunnel must be align-bored to print dims. in a real align-boring machine. You can check this out by assembling the BHJ fixture and placing the assembled block/BHJ on a large milltable or surface plate. The whole assy will rock left to right[the front and rear end plates will not sit flat @ the same time] the amount of feeler gage you can put under a corner of the front or rear will help you decide if the block needs a cam tunnel align-bore. The actual function of the fixture is to correct the int/ex angle [cam timing] and to make sure the lifter bores are 90 degs to the camshaft/lobe C/L. The amount the tunnel is OFF will also effect cam timing to an extent. Also check the thrust face of the block/cam tunnel for being sq. in both planes.

[gnicholson]

thats what i was getting at.if the cam tunnel is off then you might be causing more problems by using the fixture to locate the lifter bores. how do the aftermarket blocks usually look as far as the cam tunnel alignment and lifter bore location? thanks for taking the time to answer me.

[xenginebuilder]

thats what i was getting at.if the cam tunnel is off then you might be causing more problems by using the fixture to locate the lifter bores. how do the aftermarket blocks usually look as far as the cam tunnel alignment and lifter bore location? thanks for taking the time to answer me.

I'm pretty confident that having the lifters aligned with the cam is more important than the alignment of the cam tunnel to the crank. While it is proper and desirable for the cam to be parallel to the crank, assuming the cam tunnel is not really bad, whatever minor mis-alignment exists can be absorbed by the timing chain/belt and end play addressed with roller thrust bearings. However, if the lifters are not aligned to the cam properly, I know flat tappet cams will wear prematurely or fail on break in since the taper is neutralized, rollers see edge loading and cause lifter and cam failures from the uneven loading, besides which the cam timing cylinder to cylinder is all over the place. Of the two, I'd rather the cam and lifters were in perfect phase. JMO..
My personal experience with lifter truing was that most (not all) of the cam tunnels were pretty close to the crank centerline, at least to the extent that the fixture could be installed without binding or rocking the block. Obviously, my luck was maybe better than ALKYAL's, but we did not do that many BBC's. Saw a lot of screwed up blocks that customers were too cheap to fix though.
You can tell when you ream the bores whether the original holes were close or not to begin with, and for me BBC's and 440 Mopar's were consistently out of alignment. Some SBC blocks were close enough that I was able to bore out to .875 without a bushing, all the BBC's I did I sometimes wondered if the 1" bore for the bronze bushing was going to be enough to clean it up.
A lot of the fancy race machined blocks I saw were machined using the cam tunnel as the reference to begin with, so the crank and decks were perfectly aligned from there. I don't know if this is still how these block are machined, maybe one of the block specialists can weigh in here with an opinion. I assume that the "CNC" machining performed now as a matter of course would guarantee proper alignment, but maybe not.

[Dave Koehler]

You can tell when you ream the bores whether the original holes were close or not to begin with, and for me BBC's and 440 Mopar's were consistently out of alignment. Some SBC blocks were close enough that I was able to bore out to .875 without a bushing, all the BBC's I did I sometimes wondered if the 1" bore for the bronze bushing was going to be enough to clean it up.

Never used one of these tools but always wondered how you control drift or deflection when enlarging the hole.

[robert1]

You have a plate with drill bushings that attaches to the end plates on the block above the deck surface. Then there is a mandrel that goes in the cam tunnel that is also located by these end plates via a slot on each end. The mandrel has drill bushings also. The reamer has a long pilot that goes through the original lifter hole but doesn't locate off of it. It centers off of the mandrel and upper plate. The reamer then cuts the new hole in the proper location.

[xenginebuilder]

Never used one of these tools but always wondered how you control drift or deflection when enlarging the hole.

Dug out an old picture of the basic fixture, you can see how it captures the reamer.

[k-star]

I have done big and small chevys with the BHJ fixture and the blocks are always better after, then before. On one big block chevy it tossed 3 cams in like 5000 miles before the lifter bores were fixed, after the fix, well it's still the same cam in there.

It may not be a .0001" fixture, but it will correct the lifter bores to a perfectly usable condition.


Keith

[Wolfplace]

And the BHJ fixture in use
This was when I still had my 650

[Dave Koehler]

Anyone figured out a way to check bore position and alignment without having the bhj tool?

[robert1]

Carl and Mike use a probe in their cnc machines to verify location. I suppose if you were determined enough and wanted to waste enough time you could do it in a mill. But then you would need all of the fixturing to hold the block to do this.

[CNC BLOCKS]

Anyone figured out a way to check bore position and alignment without having the bhj tool?

Dave

As Robert mentioned we Mike and myself use the CNC machines to do our work and we are able to probe them out for location and we have a tool we made that we can actually check the lifter bore angles if needed.

One other quick way is I have a lifter bore spot facing program and if a lifter bore is of a lot it will show up there.

If anyone is interested I have my BHJ fixture for sale.

[Wolfplace]

Anyone figured out a way to check bore position and alignment without having the bhj tool?

Dave

As Robert mentioned we Mike and myself use the CNC machines to do our work and we are able to probe them out for location and we have a tool we made that we can actually check the lifter bore angles if needed.

One other quick way is I have a lifter bore spot facing program and if a lifter bore is of a lot it will show up there.

If anyone is interested I have my BHJ fixture for sale.

Nah,,, I use a tape measure
Seriously we do it like so now,,,

340 Chrysler bushings





Sm Blk Chev


How it looks when they are not where they belong,,, this is at .875, barely made .906


Carl,,
Speaking where they belong you would have loved the Bowtie block I replaced the lifter bushings in yesterday that was done by some "pro shop" at one time or another,,, I think they really did use a tape measure,,

When I got done the goddamn bushings had about 20 thou of material on one side after boring to .906 they were so far off
Went back & checked to see if I messed up with my centerline,,,
Nope, the decks were also off by about 14 thou in Y too
I cannot believe some of the crap that comes out of some places,,,