# Service bulletin SB638

A bulletin is a manufacturer's communication to its dealers, as NHTSA indexes it. The summary is NHTSA's. The document is the manufacturer's: read it at NHTSA. A bulletin is not a recall, and listing a model year does not mean every vehicle of it is concerned.

- Type: Service bulletin
- NHTSA id: 11026941
- Published by NHTSA: 2026\-01\-05
- Manufacturer's number: SB638
- Manufacturer's date: 2025\-12\-09
- NHTSA component: POWER TRAIN

## NHTSA's summary

Service Bulletin 638 advises dealers to measure and replace the camshaft drive chain tensioner.

## The document

- [NHTSA's copy of the document (PDF)](https://static.nhtsa.gov/odi/tsbs/2025/MC-11026941-0001.pdf)
- [If that address does not open, try this one](https://static.nhtsa.gov/odi/tsbs/2025/MC-11026941-9999.pdf)

The document is the manufacturer's. This site does not hold it.

## Components

Transmission and driveline

## Vehicles listed

- 2024 to 2025 TRIUMPH SCRAMBLER 400 X
- 2024 to 2025 TRIUMPH SPEED 400

## Other bulletins for the same vehicles and component

- [COM3 \- 32748](/bulletins/11026940.md), 2026-01-05, Service bulletin: POWER TRAIN. Dealer notice announcing the availability of Service Bulletin 638.

JSON: [/v1/bulletins/11026941](/v1/bulletins/11026941)

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