457 replies to this topic

[DeadSquare]

OK.

Here is another "Pearls of Wisdom before swine".

 

50 years ago, we amateurs used to put a .015" shim between the conrod and the shells,.

Do the same between the main caps and the shells.

Mount the block plus crank, rod and pistons on parallels on the milling machine.

Clock the lowest piston at TDC and nip the main caps.

Trepan the block until the lower piston is touched.

Release the mains, rotate the crank 180 deg, clock for TDC, nip the mains and traverse, the backlash decking the other two pistons.

Dis assemble, removing shims, clean, re assemble and a shilling's your uncle.

[Dusky]

OK.
Here is another "Pearls of Wisdom before swine".

50 years ago, we amateurs used to put a .015" shim between the conrod and the shells,.
Do the same between the main caps and the shells.
Mount the block plus crank, rod and pistons on parallels on the milling machine.
Clock the lowest piston at TDC and nip the main caps.
Trepan the block until the lower piston is touched.
Release the mains, rotate the crank 180 deg, clock for TDC, nip the mains and traverse, the backlash decking the other two pistons.
Dis assemble, removing shims, clean, re assemble and a shilling's your uncle.

And now your compression ratio is different in every cylinder.

[DeadSquare]

 

OK.
Here is another "Pearls of Wisdom before swine".

50 years ago, we amateurs used to put a .015" shim between the conrod and the shells,.
Do the same between the main caps and the shells.
Mount the block plus crank, rod and pistons on parallels on the milling machine.
Clock the lowest piston at TDC and nip the main caps.
Trepan the block until the lower piston is touched.
Release the mains, rotate the crank 180 deg, clock for TDC, nip the mains and traverse, the backlash decking the other two pistons.
Dis assemble, removing shims, clean, re assemble and a shilling's your uncle.

And now your compression ratio is different in every cylinder.

 

 

Only if the combustion chambers are different.

 

If the combustion chambers are the same, because the block has been decked and the pistons "decked" .015" below the top of the block, provided the rings are in tip top condition, in theory the four compression ratios should be the same.

[Dusky]

OK.
Here is another "Pearls of Wisdom before swine".

50 years ago, we amateurs used to put a .015" shim between the conrod and the shells,.
Do the same between the main caps and the shells.
Mount the block plus crank, rod and pistons on parallels on the milling machine.
Clock the lowest piston at TDC and nip the main caps.
Trepan the block until the lower piston is touched.
Release the mains, rotate the crank 180 deg, clock for TDC, nip the mains and traverse, the backlash decking the other two pistons.
Dis assemble, removing shims, clean, re assemble and a shilling's your uncle.

And now your compression ratio is different in every cylinder.

Only if the combustion chambers are different.

If the combustion chambers are the same, because the block has been decked and the pistons "decked" .015" below the top of the block, provided the rings are in tip top condition, in theory the four compression ratios should be the same.

Piston dishes wont be equal.

[DeadSquare]

 

 

 

OK.
Here is another "Pearls of Wisdom before swine".

50 years ago, we amateurs used to put a .015" shim between the conrod and the shells,.
Do the same between the main caps and the shells.
Mount the block plus crank, rod and pistons on parallels on the milling machine.
Clock the lowest piston at TDC and nip the main caps.
Trepan the block until the lower piston is touched.
Release the mains, rotate the crank 180 deg, clock for TDC, nip the mains and traverse, the backlash decking the other two pistons.
Dis assemble, removing shims, clean, re assemble and a shilling's your uncle.

And now your compression ratio is different in every cylinder.

Only if the combustion chambers are different.

If the combustion chambers are the same, because the block has been decked and the pistons "decked" .015" below the top of the block, provided the rings are in tip top condition, in theory the four compression ratios should be the same.

Piston dishes wont be equal.

 

 

Doh !..................You got me there.

 

I surrender,........................But it worked brilliantly with flat top 998 race pistons.

 

In case any one queries the .015", in those days, beer kegs came with a crimped steel cap to seal them, which had a 1/2" 'tear across strip; to unseal them,  These handy strips of steal were 28 SWG, ie .015".

[Cooperman]

I simply do the trial build with the piston rings removed. I bring each piston to TDC in turn using a DTI and then with a steel rule and feeler gauge set I measure how far each piston crown if from the deck level They are usually within about a thou or so. I then have the block deck skimmed so that the highest piston will come to within 0.005" of the block deck level at TDC.

All the other measurements can be made at this stage then the block can be fully stripped for final machining.

[JonnyAlpha]

I simply do the trial build with the piston rings removed. I bring each piston to TDC in turn using a DTI and then with a steel rule and feeler gauge set I measure how far each piston crown if from the deck level They are usually within about a thou or so. I then have the block deck skimmed so that the highest piston will come to within 0.005" of the block deck level at TDC.
All the other measurements can be made at this stage then the block can be fully stripped for final machining.

Cooperman - I am following your thinking on this one. Keep it simple, besides I don’t have the privilege of being able to custom machine it myself or pay someone to go to the extremes outlined above.
Hopefully doing the other three pistons tomorrow evening or Friday and then it’s off to the machine shop Monday for the last of the machining.
Can you look at the pic of the Conrod as I am not sure I have it the correct way around on the journal or won’t it go down the bore the other way?

[Cooperman]

The rods can only go in one way.

[JonnyAlpha]

So today I fitted the remaining pistons and then measured all of the Piston Deck Heights.

At first I tried doing it using a DTI only but this gave some crazy results, probably due to the lack of surface area on which to stand the gauge.

I then opted to bring each piston to TDC and used the steel ruler and feeler gauge method.

 

At first I measured in several points around the piston using this method:

 

 

But I then opted to measure on either side of the piston in line with the engine and then again at right angles to the engine like this:

 

 

 

Not sure which way is correct, as placing the ruler across the length of the block will not necessarily give the Deck Height of the piston in relation to the bore that it is in?

 

The block ended up like this:

 

 

This gave readings from 17.5 thou at cylinder 1 to 15.4 thou at cylinder 4. 

 

Between cylinder 4 and 3 I got the highest reading of 11 thou ?

 

In the pic above the readings along the top of the block with arrows pointing down denote the readings between the cylinders using the last method of placing a ruler along the length of the block.

 

Using Cooperman's method with the highest reading of 11 thou I would need 6 thou taken off of the block but how does the machinist do this as the deck does not seem to have a consistent height?

[Cooperman]

The machine shop will set the block up so that the deck is level to within fairly tight limites.

Don't get carried away and worry about a couple of thou difference between piston deck heights. As a guide, for every 10 thou of bore depth there is 1 cc of volume.

Unless it is a full race head, a difference of 0.5 cc between combustion chamber volumes, and this includes the volume above the piston crown, will make no difference to the way the engine performs. With race units a figure of 0.25 cc variance is normally acceptable.

Personally I would instruct the machine shop to skim the deck by 0.005 to 0.008" as this will allow them a sensible tolerance and will give you what you need.

[JonnyAlpha]

Cooperman said: "Personally I would instruct the machine shop to skim the deck by 0.005 to 0.008" as this will allow them a sensible tolerance and will give you what you need."

Do you mean get them to take off between 0.005” and 0.008” from the deck?

Edited by JonnyAlpha, 05 October 2019 - 08:43 AM.

[Dusky]

Try the dti on the side of the piston,not the center.

[JonnyAlpha]

Try the dti on the side of the piston,not the center.

 

In the pic I am using the DTI to find TDC not using it to measure the Deck Height. When using it to check Deck Height I used it on the crowns, as seen in the pic below, but when twisting it from the block to the piston I was getting inaccuracies.

 

[Cooperman]

Cooperman said: "Personally I would instruct the machine shop to skim the deck by 0.005 to 0.008" as this will allow them a sensible tolerance and will give you what you need."

Do you mean get them to take off between 0.005” and 0.008” from the deck?

 

Yes, exactly. They need to know how much to skim the block by and what tolerance you will allow them. With a 5 thou to 8 thou skim the nearest any of your pistons can come in relation to the block deck will be 0.011 - 0.008 = 0.003" and that will be fine.

[JonnyAlpha]

So I thought I'd go back a few steps just in case anyone is following this to get advice on building an engine.

 

Before fitting the crankshaft and big end bearings they need to be cleaned as they are supplied with some form of coating.

 

 

At first I cleaned them with thinners and then found it easier to use brake or carb cleaner. I also used the same method to clean the bearing housings.

 

 

Also after marking the pistons I removed the rings using a Piston Ring Spanner to avoid breaking anything. I place the rings on my bench and marked the position of each ring and to which piston they belonged.

 

 

Then taking each piston in turn, I put the big end bearing shell in the big end and applied some build lube. Before inserting the piston I rotated the crank shaft so that the big end for the piston I was inserting was at BDC (it's lowest point), this will prevent the con rod bolts hitting the journals. I also cleaned the journals with brake cleaner.

 

I then put a piece of tubing over the threaded ends and inserted the con rod into the cylinder ensuring that they were the correct way around.

 

Next I applied some ARP torque lube to the threads and bottom of the nut, put the end cap on - ensuring that there was build lube on the bearing and did up the nut up hand tight. 

 

Next I torqued the con rod nuts up to 35 ft/lbs the ARP specified setting.

 

After each piston is added you need to spin the crank ensuring that it span freely.