Bullet Proof Engine Part 2

[FRP]

Hi All.

Sorry it has taken me so inexplicably and inexcusably long to get back to this. No excuses, just busy and tired at days end.

In the first segment we covered the initial stages of block preparation. I will continue with Boring , Honing, Cylinder Wall Finish,
Block Decking and Validating the Crankshaft.

I will be discussing the processes used on iron blocks and aluminum blocks with the typical iron liners

I like to perform block decking (when required or requested) before boring. I recommend decking whenever there is any question about the surface quality of the deck or when building an engine for high out put. Some clients want me to make the call and not perform this step unless absolutely needed to save a little money. Decking is the only way to provide the most optimum head gasket surface and is the required if piston deck height is to be optimized for compression ratio and function of the squish / quench pads of the combustion chamber. Square decking is absolutely essential on any V block engine.

The block is placed in the surfacing mill and aligned with a large shaft through the main bearings. This is how the deck surface gets made not only flat but parallel with the crank centerline. The amount of material removed depends on whether you are just
establishing and new surface for the gasket or reducing deck height to set piston height.

After decking the block goes into the boring center where the block is bored to piston diameter, plus piston clearance minus .005 to .006 of an inch. Piston clearance is dependent on piston material, piston construction, block material and the type of use. The honing process will remove the last 5 to 6 thousandths to produce the finished bore.

I'll spend a little extra time here BC piston clearance and ring gaps are critical to good cylinder sealing but are an area that most frequently gets screwed up. It is imperative that the builder and the operator of the engine be on the same page if this area is to be optimized. Clearances that run toward the tighter side can only utilized with optimum safe tuning and with an operator that understands the requirement of not running the engine hard until it is fully warmed up! Generally it is safer for the builder to build in an extra .0005 to .0015 piston clearance that will save the motor if someone gets in, starts it on a cold day and starts running full boost up an entrance ramp a quarter mile from his house. Here is why. You can start out with .005 P to W clearance on a cold motor. Lets say you have an iron block. When your aluminum piston gets hammered with heat it expands very quickly. Your cold iron block - does not. Clearance is gone, piston scuffing occurs or a tight ring gap butts up and scores the cylinder.

For hi performance engines with 2618 alloy pistons the clearance recommended by the piston manufacturer can vary between .0035 and .005 of an inch. * Note These are recommended clearances and it is incumbent upon the engine builder to know how to vary the clearance based on how the engine will be used. I personally never use clearances tighter than .004 on aluminum blocks with iron liners and never less than .0045 on iron blocks on hot street motors if I trust the operator. For real high output stuff or if I don't trust the operator minimums go up to .0045 and .005 respectively. "Clearance is your friend".

Honing is the single most critical determinant of ring seal and longevity. Roundness and straightness of the bore is critical. It is imperative that the surface finish retains the proper amount of oil without retaining so much that rings hydro - plane.

Modern honing technique involves a process called "plataue honing". The basics of this are the use of 2 to 3 stones of increasingly finer grit.
The term plateau refers to the surface established by the final stone and is the surface actually contacted by the piston rings. As the term implies there are "valleys" between the plateaus that were left from the honing done with the rougher grit stones earlier in the process.

Cylinder wall finish is represented by the terms RA or roughness average. Rpk which is average peak height and Rvk which is average valley depth. The term Rk refers to the average width of the plateaus. Engine builders tend to develop their own formulas for achieving the final RA based on their own experience. Dart Machinery only uses a two stone process with a 250 and then 500 grit diamond hone to finish. The majority of the material is removed with the 250 and the 500 is only used on the last .0005 of an inch. This process leaves substantial valley depth because no intermediate stone is used. Other builders prefer much lower RA's and lower Rvk. I use a process of three stones and only remove .0003 with the final 500 grit stone which leaves less Rvk but plenty of moderate valley depth for oil retention while producing what I feel is a longer lasting more durable bore finish which is less subject to clearance growth over time.

The last variable is cross hatch angle and it is also critical. Cross hatch angle strongly affects oil retention and the ability of the oil ring and second ring to remove just the right amount of oil from the cylinder wall while leaving enough behind to support the piston load and lube the hot top ring. It is imperative that the builder understand the competing issues involved in cylinder wall finishing, as ring width, ring tension,
cylinder loading (pressure) rpm range and ring material all affect the final outcome.

Regarding the validation of the crankshaft everything is pretty much straight forward. Assuming the crank has had no major trauma such as spun bearings or rod and piston blow ups, it is a matter of a lot of very precise measurement to insure that all of the journals are round (concentricity) and flat. Both of these metrics are highly critical to bearing life especially in hi boost small displacement turbo motors as it is impossible to maintain a high quality hydrodynamic wedge of oil between the crank and the bearing surface in the absence of journal flatness and concentricity.

The journals are all checked with a .0001 resolution micrometer to determine the aforementioned qualities. Both concentricity and flatness should be held to .0002 or below for high performance work.

Lastly the crank is placed in lathe centers (or upper bearing shells in the front and rear main positions of then inverted engine block) and a dial gauge is used to measure total run out at the interior main journals with the center journal measurement being most critical. This tells us whether the crank is straight or "bent". I won't run a crank that has more than .001 at the center journal until it is straightened. Good crankshaft shops (Mile High Cranks in Denver Co. is my choice) can make them perfectly straight again. It is very common for Audi five cylinder cranks to be bent if they have had oil starvation issues and heated up a rod journal. The thermal expansion of the small concentrated journal area pushes the crank out of line and they have to be straightened.

Hope you find this of benefit. I'll be quicker with the next post nd will go over bottom end assembly. Cheers and Happy Thanksgiving.

[varia]

excellent, as always. thank you
Happy Thanksgiving too

[PRA4WX]

I'm thankful for these posts!

[chaloux]

Freaking awesome. Thanks Jeff, I really appreciate the time you put in here.

[All_Euro]

Thanks Jeff - really enjoy your input.

[FRP]

You are all welcome. I'll get the next post done soon to keep this series moving. Happy T Day.

[PRY4SNO]

Well done, yet again.

Always interesting to learn how much detail goes into properly building a high output engine.

[ringbearer]

This whole series makes me want to ship my engine to FRP when the time comes. I'm not after one million horsepowers but I want it done right the first time.

Thanks again for sharing your skillset with us Jeff!

[Urtorsen]

Brilliant read


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