302 to 331 On a Rock Bottom Budget - Part 2

[DavidVizard-GFN]

Ford Mustang 302 to 331 – On a Rock Bottom Budget!

Part 2

Text, photo’s and drawings

by

David Vizard

Here’s how to save money on the block for a stroker 331 or 347.




#1 The block used to build this 331 in our shop was anything but expensive. In this installment we will show you what you can do to make a race worthy block for as little as $75!

In part 1 of this story we looked at the parts sold by Pro Power for a really low cost rotating assembly to build a stroker similar to the one you see nearby. But having a functional rotating assembly is only part of the battle – you will need a block as well. If you are rebuilding the engine from your existing (and hopefully well maintained) 302 or getting even a reasonably well maintained short block from a wrecking yard, then there is some good news. The fuel injected 5.0’s have a far better air fuel calibration during cold start than a carbureted engine. This, plus better overall calibration, leads to a dramatic reduction in fuel wash on the bores. The result is the bores wear very little and you can, as often as not, find the block has little or no ridge at the top of the bore. This is good as it opens up an avenue for a super cheap bore reconditioning job. Here’s the deal – Ford hones the blocks at the factory without the aid of a deck plate to simulate the distorting stresses caused by bolting down the heads. Couple this to the fact that the bores are very thin on a 5.0 block (thin wall casting technique) and you will understand that the 5.0 is not the best when it comes to perfectly round bores. If you send your block to a good race engine shop be honed they will do so with a deck plate. However you need to be aware that the walls are thin enough that removing and replacing the deck plate will result in the bores measuring slightly different each time. In other words the bores are flexible. What this means is that though a deck plate honing job is good it is not as effective as it is on a thicker walled block such as the 351. With a brand new engine from Ford we have to tolerate less than super accurate bores. This being the case we can also live with them being equally inaccurate at rebuild time though having something a little better as delivered by deck plate honing is still worthwhile. This being the case if the bores have near zero existing wear they can be refurbished ready for further use by glaze busting with a $29, three stone, glaze buster from NAPA.

#2 This little device, a three shoe glaze buster, can be had from NAPA for about $29 and can be used to bring near zero wear bores back to as new condition with an electric drill.

At this point you may be thinking that with no bore micrometer to measure the bore and no deck plate, a set of bores cleaned up with a glaze buster will produce anything but a decent race prep job. Let me put it this way – if you have not got the cash for a deck plate honing job then that’s it – this is your next best move and it will be just as good as the original factory bore job!

What to Do.

Op #1 on our ‘micro budget’ block is to really clean it both inside and out. Here the procedure involves taking the newly stripped block and, with an electric drill powered wire brush and Gunk, get the worst of the grunge off the outside. Use liberal quantities of water from a high pressure hose to wash everything clear. Cleaning up the blocks cylinder head deck surface can also be a chore but needs to be done well. This can be tackled by taking a piece of flat 2 x 4 wood about a foot or so long and, using thumb tacks, fix, in a length wise direction, a strip of 80 to 100 grit emery cloth to it. This gives a good tool to rub over the deck face without getting the emery hung up on the edges of the bores. Here you are not attempting to clean up the head face so much as to clean up the area that the previous head gasket actually contacted the block to form the seal required. There will be those areas, especially around the water jacket holes that will, due to corrosion, be below the original machined surface and will not clean up. This you are stuck with but it is of no real concern.

The next op is to prep the bores. Now let’s be clear on one thing here. The operation about to be described applies only to bores with minimal wear, that is up to about a half thousandths of an inch (0.0005). This limit can easily be determined without the aid of a precision bore mic. All you need is a set of feeler gauges and an old piston ring that was previously in the engine. Here’s how to check. Install the ring and square it up about ½ inch down the bore by using a piston with only the second ring in it. That second ring will act as a stop on the block face and square the ring. Check the end gap. Now position the ring right at the top of the ring travel as indicated by the wear pattern. Do this with enough care to ensure that the ring is square in the bore. Measure the end gap. If it is bigger by two thousandths (0.002) or more then you should really be considering a rebore.

At this point you should be ready to clean up those bores. This involves loading the glaze buster into a relatively slow electric drill. All that is needed here is 200 - 300 rpm max. Spray the bore being worked with WD 40, compress the glaze buster legs and install it in the bore. Spin the glaze buster at a speed you are comfortable with and work it evenly up and down the bore taking care not to hit the mains housings. One strike here usually means a shattered stone so take it easy.

#3 Since there is a ton of other engine degreasers on the market you may well ask why use Gunk? Simple answer here, other than cost and availability, is that it leaves a slightly oily surface after hosing down which gives you time to WD 40 the machined surfaces to minimize rusting.

With about a half thousandths bore wear to contend with figure it will take about two hours to prep the bores. When the glaze busting has been completed give the block a provisional Gunk and wash. Next, using a new scotchbrite kitchen pad, wipe the bores in a vertical motion for a couple of minutes each.

#4 Here is what a previously used bore looks like after reworking it with a glaze buster and Scotchbrite.

To get a stroker assembly to clear everything it is necessary to do a little metal removal at the bottom of the block bores. The nearby shot shows typically where and by how much.

#5 Indicated here is the notch to clear the rod. This one is clearance for a 331. for a 347 the clearance needs to be about 0.075 more.

The way to do this is to install the crank with just #1 and 5 bearings in the block. Next mount a ringless piston on a rod and install this in each bore in turn and check the position of, and amount, to be removed. Mark with a felt tip marker. Remove the crank and, using a carbide (not a grinding wheel), cut out the interfering material. This will usually take several trial fits before it’s done satisfactorily. You are looking to get about a 1/16 inch clearance.

If you are to avoid the cost of new cam bearings and the R&R of such then particular attention to the oil passage between the main bearings housings and the cam bearings is needed. Either during the cleaning process or, the use of the engine if it was infrequently serviced, unwanted dirt can get into these passages. Every so often go back to these passages and re-gunk and wash them out and also make sure that when the rest of the block is clean these are the last parts to be washed out. Part of the cleaning is also going to involve cleaning all the block threads. A cheap tap and die set here will give you the tools to do a good job – and it does need to be good. If the head bolt threads are dirty and the bolt torque is not translated into the correct clamping force then a head gasket failure is in the finished engines near future.

When clearancing, bore work, thread cleaning and any other op that produces debris is done go through and do the thorough and final Gunk and wash. At this point a source of high pressure air to blow everything through or down is a definite advantage. If this is not available then wipe everything down using kitchen towels until most of the water is gone. Then spray WD 40 through the oil galleys and anywhere else water may collect. The WD 40 is good at displacing water. Wipe off the excess WD 40 and repeat the op until you are satisfied that the block has had all the water removed.


If replacement of the cam bearings is required then figure that a typical machine shop cost for removing and replacing them is between $50 and $75 including the new bearings. Have this done as a last op after all the cleaning is 100% finished. While the bearings are out have the machine shop blow through the oil holes between the mains and cam bearings.

At this point the block is ready for painting. Degrease all the cast surfaces to be painted and the machined surfaces that will need to have masking tape stuck on them. Next mask up the block, give it a couple of coats of primer, then the same treatment with an engine enamel. A finished example is as seen below.

#6 Here is a finished example of a 331 block done in the GFN shop for about $20 but we already had the glaze buster and a set of cheapo taps for cleaning threads. Throwing a glaze buster and taps into the cost leaves this as about a $70-75 job plus a full week-ends work.

An Alternative Approach for a Stroker Block

Maybe you don’t want to do your own block after all time is also money and getting a dirty block clean in what might be a nice clean garage may not appeal to you. From all the forgoing you can see there is quite a bit to getting a decent block. But let’s go for something that is far less of a compromise. These days having a block stripped, cleaned, bored, decked, mains aligned checked/honed and painted can, at a typical quality machine shop, cost about $400 to $500. All this being done on your block whether it was near ideal for the job or not. If the block does require boring, as will be the case in about half the instances we see, then it’s machine shop time and costs go up accordingly.

#7 You can get a fully prepped CNC machined block like this from DSS Racing for an outright price of $625. A selected block with stroker clearance machined in and premium accuracy make this a very cost effective deal. If it is a basic selected block, bored, decked And painted ready for yoy to assemble your parts into DSS has a level II block at $495.

However if you can afford to shell out $625 you can get a great deal from DSS. This company has invested a very large amount of money in CNC equipment that will machine a truly race ready stroker block to super fine tolerances. On top of this it does so at a far faster rate than conventional equipment in most machine shops. The result is a very cost effective precision product. If $625 is still over your budget for a race prepped block then check out their Level II block at $495!

Here’s how it goes. First DSS strips a provisionally checked selected block and cleans it down to bare metal. The block then has all the threads re-tapped. From here it is then stroker clearanced, bored, decked square, mains alignment check/honed and the bores deck plate honed. In addition to installing new cam bearings and thrust plate most of the oil galleys are tapped to take pipe plugs instead of drive fit plugs and the lifter bores are re-honed. Lastly it is primered and enameled.

The basic Level 10 stroker block from DSS will cost you $625 and that is an outright cost so you still have your block. This you can either keep as a spare to work on later or sell to some one who is doing a more basic rebuild. Also you have the benefit of DSS’s block selection. Any block that is not up to scratch is thrown out before ever going through the system.

#8 The DSS Level 1 and 2 CNC stroker blocks will take the stroke length needed for up to 347 inches. The quality of machining on these blocks is excellent and the price extremely competitive. Note the screw in oil galley cross-over plug toward the top right hand side of the photo.

Should you be able to afford something a little more money DSS also does a Level 20 block. The selection parameters are a little more stringent for a block to be used as a level 20 item and a few more ops are done to help build more power. The most noticeable of the upgrades is the screw-in freeze plugs. These are intended to add a little more stiffness to the sides of the block. At the top of the bores in the quadrant around where the intake valve is located when the heads are on is a 60 degree CNC machined chamfer. This allows the air passing around the cylinder wall side of the valve to make the transition from the cylinder head into the bore easier thus producing a small, but non-the-less, helpful increase in breathing.

#9 The arrow on the right indicated the CNC machined rod clearance slot in the bottom of the bore. The other arrow shows the line honing in the mains of these DSS blocks.

# 10 The enlarged chamfer indicated has the effect of slightly reducing valve shrouding on the cylinder wall side of the intake valve.

In the GFN shop we have built almost a dozen engines using DSS CNC blocks. Every one of those engines has performed well. Based on our experience to date building lower budget strokers we would recommend this block program to anyone. Based on the fact that very little of anything is perfect we give this product, on the GFN star award rating, 4.9 out of 5. What that means is it rates in the top few percent of stuff you can buy for your performance engine.

What’s Next?

At this point you could have the key parts for a short block assembly that owes you about $1325 if you went the DSS route for a block or about $775 if you did your own block work. That extra displacement is going to be worth extra output no matter what but actually making the most of it requires a little more understanding of what is going on. To complete the short block a cam and timing set will be needed. Sure you will have this if you stripped a motor for the block but don’t think for one moment the cam events will be optimal even if they were (and that’s highly unlikely) when the motor was a 302. In the next installment you will get the lowdown on what a stroker engine needs in the way of a cam – and what you will learn probably has not been printed outside of anything I have previously written.

David Vizard

[custom40]

David,

This is a great series - I am in the middle of a 331 stroker build and am somewhat stalled trying to decide on the cam. The car is a 1940 ford, 2-door sedan hot rod. 331 sbf, 10.25:1 CR, GT40 EFI intake, Dart 170 aluminum heads as-cast. I plan on running a warmed-up AOD with a 3.55-ish 9" rear. Rear tires are about 29" tall. I want this to be a reliable, high performance car that I can drive coast-to-coast.

Got any ideas or suggestions for the (hydraulic roller) cam?

Thanks for the great articles!

Andy