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Setting bearing clearances on B-Series engines

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Setting bearing clearances on B-Series engines

Postby HondaB20B » October 4th, 2006, 9:11 pm

Setting the bearing clearances was a problem that I encountered during my engine build up. I used brand new rods, a micropolished crank, and a Dart block, non of which contain factory stamps for bearing sizes. It took me a while to figure everything out, and there wasn't a decent write up out there that people can use, so I decided to make this available for people like me!

Tools Needed:

- 1-2" Micrometer
- 2-3" Micrometer
- Set of telescoping gauges
- Plastigauge
- Torque wrench


Before measuring, make sure all the surfaces are clean. Use some break cleaner to clean the surfaces.

Measuring the Crank Caps:

Start by torquing down the crank caps to the factory spec. Expand the 2-1/8 - 3-1/2 telescoping gauge in the crank cap. Make sure angle between the gauge handle and the crank cap plane is 90*, otherwise you won't get an accurate reading. Once the telescoping gauge is in the correct position, lock it. Remove it from the crank cap and measure it using the 2-3" micrometer. Do this several times at different spots. That both reduces the chance of error, and tells you if the crank tunnel is perfectly round or not. Record the data.

Measuring the Rod Caps:

The next step is to measure the rod cap diameter. Torque the rod down according to the spec sheet. Insert the 1-1/4 - 2-1/8 in the rod cap and expand it. Make sure the handle is at a 90* angle with rod cap plane. Measure this at several spots, and use the 1-2" micrometer to measure the diameter of the rod cap. Record the data.

Measuring the Crank Journals:

The next step is to measure the crank journals. Honda recommends measuring each journal at 4 different spots, approximately 45* from each other. I don't like and cannot afford to take a chance with my engine, so I like to measure at every 10* to make sure the crank is perfectly round. Start by measuring the main journal #1. Use the 2-3" micrometer to measure this journal. Open up the micrometer and place it around the journal. Be careful not to scratch the journals. Tighten the micrometer until it hits the crank journal. Once it hits it, you can tighten the micrometer more, but DO NOT DO THAT. Record the diameter of the journal at that point and move on to the next. Do the same steps for every journals. For rod journals, you need to use the 1-2" micrometer, but the rest is the same. It is also good to have a Honda manual handy so you can compare you data with the OEM specs to make sure your crank is not too much out of round or....


Once you have collected all your data, it's time to do some calculation. These are the actual data I gathered while I was measuring my engine parts. The crank was micropolished, the rods were brand new Eagles, and the block was align-honed.


Since the block was align honed, all the caps measured 2.3225".

The rods also measured 1.8900" for all 4 of them, which by the way is dead on the Honda specs.

This is the bearing thickness chart from Honda (B-series motors only).

Now you have all the pieces to the puzzle. All you have to do is to decide on a clearance. I'm building a turbo motor and the recommended clearance for such motor is between .0015" to .002". You can use the following equation to
determine the size of the bearing:

Bearing Clearance = Cap Diameter - Crank Journal Diameter - (2 x Bearing Thickness)

So for my case, in order the obtain the 0.0015" clearance on the mains, I have the following:

0.0015 = 2.3225 - 2.1644 - (2x)

Now all that needs to be done is to solve for X and that would give you the bearing thickness. Then compare the thickness with the color chart and pick the corresponding color. In my case, I need to order red main bearings to obtain the desired clearance.


All that needs to be done now is to double check the clearances with plastigauge. Install everything in its place. Place a strip of plastigauge on the crank journal and torque the cap down to the factory spec. Now unbolt the crank cap and measure the squeeshed piece of plastigauge with the comparison chart that comes with it. Hopefully your clearances are what you have picked!

Happy measuring !!

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Postby Zh@ne » October 4th, 2006, 9:52 pm

nice info there!...but how often would a man go through this?

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Postby Spyrogyra » October 6th, 2006, 11:01 am



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Postby X2 » October 6th, 2006, 11:29 am

Zh@ne wrote:nice info there!...but how often would a man go through this?

Only on a complete rebuild... not for beginners.

Dean meng... give the writer some credit dey nah !!

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Postby Zh@ne » October 19th, 2006, 12:26 pm

....well done sir..."better!"


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