MM-MAR10083100 - Maruha Motors connecting rods

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Part #: MM-MAR10083100
Your Price: $163.64

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Product Description

Inside an engine, the parts have to work under strict conditions would be RODS.

Tuning for hi-revving and souped up engines bring on any stress and it attacks the connecting rods directly.
In some cases they can bend or snap and these lead to broken engine. Complications with rods are the most severe case, and we have to care about the rod’s performance so much when we assemble an expensive tuning engine.

The low performance of rods leads to the damage to metal bearings. There are two types of bearings. One is for rods and another is for main journals and the bearings that have to function under the more severe conditions is ones for connecting rods.

When we assemble an engine, we take care of the crankshaft by checking revised bends and lapping of journals, confirm metal bearing clearance, check oil pressure, try reducing piston friction. Any engine has to be assembled with these greatest attentions.

However, with higher rpm and increased power, one thing comes out in spite of attentions.
The typical cause is the deformation of rod bearings.  

With going up and down at high engine speed, a pure circle of a big end is becoming oval, an elliptical big end give big damage to metal bearings.

Oil clearance between metal bearings and crank journals extinct by elliptical big ends, and happen metal bearing troubles.
And that opening between bearing back plate and big end inside of rods occur by deformation, oil flow into these openings and vibration brings corrosion.

Metal bearing receive damages from both side by close in phenomenon. 

We can say that high performance rods are absolutely necessary on engine tuning.

1. I-beam type : 
Maruha Power Rods are I-beam rods which are excellent in strength. This rod is specially designed for Miata BP racing engine (1800cc) and can keep the great high performance under aimed high-revs.

Because this rod is analyzed by engineers (with FEM) they are very suitable for each dimensions. For example, a neck width was calculated on every 1mm modification.

Light weight and strength are factors that meet on a good balance. We never focus only on light weight because it is difficult to balance both factors properly.

Maruha power rods have a light weight of approximately 100g compared to stock rods. However, there was much effort to reduce only 1g.

2. Strong bolts
Maruha power rods use bolts from the greatest bolt manufacturer ARP Inc. We also adapt larger OD bolts than other rods. These ARP bolts are waist type and can control the correct extension stress.

Regarding cap meet at the big end, very complicated machining processes were performed to keep balance between weight and strength.

Also every part is designed with the suitable width and thickness. End cap is fixed by the use of a bolt (unlike stock which use nuts) The shoulder has a very smooth appearance which is very effective for strength.

To fix cap position, nock pins are installed. Then you can lock caps correctly. This correct and tough fixing is strong against vibration and improves metal bearings to be more steady.

3. Stress at DC (Dead Center)
Bore size, stroke, metal width, compression, IG timing and engine power are factors that all affect metal bearings. But, we have to consider more about severe point for rods.

In the case of the BP engine (1800cc), assumed piston weight is 400g over 9,000rpm. This is our base design for rods.

Exhaust DC means that after burning in a chamber, piston go down so fast and continues going up keeping fast to the max upper point.

If it is intake DC, compression like brakes can reduce piston speed. Pistons want to go through up a cylinder head and pull out a rod from a crankshaft because of their strong inertia.

A crankshaft wants to pull a piston down forcefully. Heavy pistons, high-rpm, more power all affect rod stress. Maruha Power Rods are designed against rod stress up to a couple of tons by using FEM analyze.

4. Small end.
Small end has a fully floating process with bushes for high engine speed. ID of small end is the same size as stock rods, any pistons for Miata with a base pin size can be available for our rods.
There is a tapered oil hole at the top to help for a smooth surface for dropping lubricants.

5. Weight balance
Whole weight is always measured, but we check at each end weight.
This precision machining is one of our features for the Maruha power rods.

Usually mechanics adjust only the whole weight, if you want more hi-level technique, you have to think about each end weight in details.

Because the big end catches up with the crank journal and small end connects to piston pin.

Thus from a view point of inertia, rods work separately from big end and small end. Therefore weight balance on each end is important.