Bigger's better
I'm testing the 12 bolt as well. Done about all to it that I can (welded tubes, Large Ford ends Steel Cap w/half inch bolts, 35 slpine axles and spool and a girdle) so it will either live or die.

 

Bowties have a cleaner finish, IMHO. Dart has several dead giveaways, most noticeably the scallops under the bores. New
Bowties start as Gen style 1pc RMS but has a factory installed Mark version 2pc RMS adapter. Still has the taller lifter bores - sorry you don't want to buy new ones, but taller is better, particularly for the lifter bores. If you find a dogbone style that you like, the Bowtie has lifter valley provisions for a hold-down, Dart doesn't.

 

Why not 540 with the Dart?

 

Was just hoping to not buy new lifters and push rods. But since they both have taller lifter bores looks like I'm stuck. Here's a picture of the bores. Seemed to run fine but was leaking coolant into 6 which is the pics with the drip down the bore. Other pic is cyl 8 which had no coolant leak. Not deep but I can feel it with my nail.

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Or I try and clean the cylinder a bit with a 3 stone then a ball and put it back together and run it till it dies lol.

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Why not have the block decked and honed, have the heads surfaced and reassemble everything. Looks like you have a lot of nice parts there.

 

Why not go to a 540 here is a link for a 2 piece rear seal Bowtie block Chevy 19212191: Bow Tie Sportsman Engine Block, Standard | JEGS

Why does you block have O-rings ?

 

It's an old LS6 and has been decked over the years and the pistons come .014 out of the hole. So the previous owner (a machinist) o-ringed it and threw on a .062 copper head gasket for ptv clearance. And for some reason it was getting water in cyl 6 so I pulled it apart.

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This is the bottom side of cyl 6 gasket. Looks like cylinder 2 was about to go.

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It's my understanding that Bow Tie blocks are now sourced by GM from Dart.

Your problem with the head gasket is kind of common, two cylinders on each side are "missing" a head bolt.

The after market blocks (including Bow Tie blocks) have the bolt slots to add in an additional bolt to these cylinders that's wrenched from the lifter valley before the intake manifold is installed.

 

Those decks on an OEM block are pretty frail I don't think you would see this on a Dart block or should I say this has never been an issue with a Dart block.

 

You can buy pretty much any thickness gasket you want from Cometic.

 

Carl, I "think" he's talking about the Bow tie race blocks.
Does that make a difference?
Chevy Performance BBC Bow Tie Race Engine Blocks | JEGS

 

I am referring to the sportsman blocks. I plan to keep it all motor and spray a small shot when I'm feeling froggy lol.

 

dont they make a CNC bowtie block?

 

Chevy Performance BBC Bow Tie Race Engine Blocks | JEGS

Cast Iron Bow Tie Race Block Technical Notes
Precision CNC-machining means +/- 0.001'' tolerances
Standard deck (9.800'') or tall deck (10.200'')
4.240'' Finish Bore (4.600'' Maximum Bore, .250'' Minimum Wall Thickness)
A sonic bore check data sheet is provided with each block
Lifter bores are .300'' taller than standard blocks
Siamese cylinder bores
Improved cooling around number 1 cylinder
Accepts Mark IV or Gen V, Gen VI cylinder heads
Use Gen V head gaskets with Mark IV and Gen V cylinder heads
Use Gen VI head gaskets with Gen VI cylinder heads
Requires Mark IV design 2-piece rear main seal oil pans
Requires Mark IV design crankshafts
Can use Mark IV and Gen V, Gen VI camshafts, timing sets, lifters and timing cover
(aftermarket belt drive timing covers may require clearancing)
Blind-tapped head bolt holes; extra inner head bolt bosses provided
4-bolt SAE 8620 main caps splayed 16° on the three center mains
Priority main oiling wet sump system
Provisions for dry sump oil line provided
Honed camshaft and crankshaft bores
0.842'' lifter bores (maximum 1.06'') may be relocated
Distributor gear clearance at bottom of number 8 cylinder bore should be checked
Machined mechanical fuel pump pad
Tested to 1,200 horsepower!

 

I believe the Bow Tie blocks have thicker decks. They do have blind head bolt holes.

The blocks rated to 800 HP have nodular iron main caps, 1,200 HP rated blocks have steel caps.

 

SMH

I keep throwing money at this Mark IV I will NEVER get my Big M...

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Jesus I just need my Mark IV to disappear.

Every time I turn around it takes me farther from my Big M goal.

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I still have my old Merlin II block after 14 years. :crying:

And my 12 bolt.

 

I still have my old Merlin II block after 14 years. :crying:

LOL...me too...except it's been 17 years.


It's been a great block and handled lots of abuse!


JIM

 

Dart is a great block but they have one inherent oiling problem that Dart refuses to acknowledge as a "problem", but needs to be addressed especially if running hyd. lifters.

 

Like what?

Do tell, inquiring minds gots to know.

 

Dart is a great block but they have one inherent oiling problem that Dart refuses to acknowledge as a "problem", but needs to be addressed especially if running hyd. lifters.



Like what?

 

Looks like I might go with the merlin 3 block. That way I can just swap everything over (solid lifters, push rods) keep it 505ci and afford some aluminum heads.

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I've had Bowtie Sportsman and CNC blocks side by side on engine stands and other than the steel caps, I haven't been able to find any real differences in them. I haven't sonic checked for thickness of cylinder walls, etc., but to the naked eye, they look almost identical.
I snagged a Sportsman from a local racer after he'd run it for a couple of seasons at 4.625" bore. It has .903 bronze lifter bores and will easily hone at 4.630. Since it will run N/A, I don't have any doubts it'll handle more than I can throw at it. I grabbed a new Scat 3.76" stroke crank last year for it, this is the newer style with center counterweights. If I ever get it built, I'm going to buzz this beyotch to the moon!

 

For about 2 years now we started modifying every block regardless of brand so the oiling to the top doesn't get interrupted when the lifters are at "peak" lifts.

Not sure if this is what Scott is referring to but it's an area that needs attention anyway!

It's compounded when lobe lifts rise above .400". The brand of lifters also comes into play, some are fine "as-is", some don't make it.

Before we fabricated some tooling to modify the lifter bores we would occasionally modify the lifters themselves to solve the issue, problem was when they went to direct oiling to the wheels with the small EDM hole we weren't comfortable with "grinding" on the lifters anymore. We needed a better method!

We now "sight" the lifters in the bores at max lift (directly through the front oil galley with the oil plug not in place) at full lift during the mock-up period on almost every race build. This gets done with the correct parts for the build, leaves no room for error.

Thanks, Gary in N.Y.

P.S. Here's a couple shots to explain some of what I'm saying. One is how we use to modify the lifters, the other how we do the blocks now! Really not necessary on the lifters anymore. Takes us about 20 minutes per block to do the 32 slots.

 

Comp lifters are way to short of a lifter compared to other lifters out there.


No matter if your running a .300 lobe or a .500 lobe at max lift the lifter will be at the same height.

I would think there would be a bigger problem with the 55MM cams and so far no problems, I do modify lifters on the rear of the block as I groove between the oil band and the oil holes.

 

Gary, It looks like you are grinding a little chamfer ^ the lifter bore to keep the oil band getting oil at max lift?
X2 on the brand of lifter.

 

When you say height, do you mean the oil band on all lifters are the same?

 

This will be a video of information. We are selling anything. We give the dimensions to make the plug and how to install it. Anyone with access to a lathe can have both the install tool and the plug made. We feel our experience and this modification will will help many in the hotrodding community.

 

This has been a long-known issue with Dart more than any other vendors!

Years ago it made us look into keeping a real good supply of a asst'd pipe plug sizes AND lengths. We find many times we need "shorter" plugs on the SBC's over the cam gear at the front of the blocks also.

Thanks, Gary in N.Y.

P.S. Ever since we put this plug pkge together we haven't found it necessary to re-tap one single hole any deeper, even on the Darts!

 

Gary
I have been down this road & my results differ so I check every one as a matter of course & yes many in fact most no longer seem to need retapping

That said.........
I don't care how long the plug is if it does not go in to begin with more than a couple of threads I retap the hole.
Just because the plug is shorter has nothing to do with the beginning diameter of the taper. In fact if it did the longer ones would conceivably start smaller & install deeper even if sticking out further

 

Well back on topic I found a guy selling a billet cap bowtie block brand new never been machined that he bought in 1995. This thing has been wrapped up tight and sitting under his bench since then and still have the paperwork for it.

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So, have you jumped on it? Care to share the asking price? I have a couple stashed away that I bought in about '05. GM lost their mind and ran them on a sale cheaper than nodular capped Big M's for about a week, I figured they were a decent investment.
Looks like a Gen 5 (they don't have Gen 6 Bowtie Blocks that I'm aware of) with the RMS adapter on the block and a conventional 1-pc RMS main cap.

 

They are machined, with sheets as above?

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