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An engine block alignment check measures whether the main bearing bores, the saddles that hold the crankshaft, still sit in a straight line. Route 66 Auto Repair in Upland recommends it during a rebuild, after a spun main bearing, or when a new crank wears its bearings unevenly. A crooked line bends the crank slightly on every turn. Our ASE-certified technicians check straightness and bore size, and your written estimate shows every step, including any correction the results call for.
When should main bore alignment be checked?
- A spun main bearing that may have heated the block
- Uneven wear on the upper or lower main bearing shells
- A crankshaft that binds when the main caps are torqued
- An engine that ran with low oil pressure for a long time
- Any full rebuild on a high-mileage block
What does the check tell us?
We look at two things. Straightness, checked with a precision straightedge or arbor, shows whether the bores line up from front to back. Size and roundness, checked with a bore gauge with the caps torqued, show whether any bore has stretched or gone oval.
Worn or oval bores make new bearings fit wrong no matter how good the crankshaft is. That is why we check before approving main bearing replacement on a block with a history of bearing trouble.
Our block alignment check process
Step 1: Clean the saddles
Bores and caps are cleaned to bare metal; your written estimate shows every step.
Step 2: Torque the caps
Main caps go on in order and are torqued to spec without bearings.
Step 3: Measure size
Each bore is gauged at several angles to check size and roundness.
Step 4: Check straightness
A straightedge or arbor shows whether the bores line up.
Step 5: Report and advise
Readings go on the repair order with the spec and a recommendation.
What's included in an engine block alignment check
Included on the work order
- 01Main cap torque to spec
- 02Bore size and roundness readings
- 03Front-to-rear straightness check
- 04Cap fit and register inspection
- 05Written readings with factory specs
- 06Correction options if out of spec
Is a block alignment check need-now or need-later?
Need now: call
- After a spun main bearing, before new parts go in
- Uneven bearing wear found at teardown
Need later: book
- A rebuild on a block with no bearing history, where it is good practice but optional
- A running engine with normal oil pressure
How pricing and timing work
This check happens on a bare block, so it is priced as part of the rebuild or teardown. If readings are out of spec, correction adds cost and time, and we stop and call before any of it. Your written estimate shows every step. AAA members save 10% on parts and labor, up to $75. For the overall job, see engine rebuilding, or call (909) 608-7699.
What happens next
If the bores are straight and round, the block moves on to bearing fit and assembly. If not, you choose a correction or another block with the readings in front of you.
Frequently asked questions
Is this related to wheel alignment?
No. This check is inside the engine and concerns the crankshaft bores. It has nothing to do with the wheels or steering.
Can a spun bearing damage the block?
Yes. The heat from a spun bearing can distort the bore. That is why we measure before fitting new bearings.
Is the check always needed on a rebuild?
Not always, but it is wise on high-mileage blocks or any engine with a bearing failure. We explain the reason when we recommend it.