Technical: Valves and Tappets
Stan Diener, Jerry Raino, Dave Hennessey

This article is under development

1952 - 1956 K and KH


18070-52 Intake valve (2) 52 & 53 –Model K & later 53 – KK
18070-54 Intake valve (2) 54 to 56 – Model KH, KHK
  also 54-57 KHR, 58-E59 KR
18080-52 Exhaust valve (2) 52 to 56 – All K Models except early 53 – KK
18070-41R Intake valve (2) Early 53 – Model KK
18080-41R Exhaust valve (2) Early 53 – Model KK

Here is Stan's NOS valve collection. The early 1953 KKs used the same valves as the WR racers. Partway through the 1953 model year, the KKs changed to use the standard K valves.


The K and KH used the same 18490-29 tappet, but the taller KH cylinders required a longer tappet screw. The 1953 KK and 1956 KHK used the KR tappet. The 1953 KK used the hollow KR tappet screw. The 1956 KHK used the standard KH screw (the KR screw was too short for the KH cylinders).

The tappets used in the 1955 KHK (and the few 1954 KHK) are a bit of a mystery. We think they used the 18508-52R tappets, but we have conflicting factory documentation. The September 1955 (1956 New Model Announcement issue) of The Enthusiast tells us the 1955 KHK “special roller tappets are lighter in weight”. But the 1956 Spare Parts Catalog tells us the 18508-52R were only used on the 1953 KK and 1956 KHK. So either the Enthusiast made us a promise it couldn't keep, or the parts catalog guy was asleep at the handlebars.

Tappet Guide Screw and Washer

Jerry's Collection of Crusty-Rusty K-model Tappet Guides and Screws

Check out the 52 K 1001 - Factory Photo #19631 on the Literature page. Click the photo, then click the SuperSize button, and you can see the Phillips head tappet guide screws on 52 K 1001.

1957 - 1969 Sportster


The OHV Sportster changed most things in the valve train. This new valve train remained almost unchanged from 1957 through 1969, but there were some strange twists in the tappet department - and again, some conflicting factory documentation.

The 1957 Sportster brought with it a new tappet, the 18523-57, and along with it, a new tappet screw, the 18554-57. This new tappet was used on the 1957 XL, and probably on the 1958 and 1959 XL. In 1958, the XLH and XLCH reverted to the 18508-52 tappet, but retained the new 18554-57 tappet screw. We think that the 18508-52 tappet was the same as 18508-52R used on the KR and some Ks, but the -52R was shortened to -52, since it was now a regular production part, and no longer a racing part.

The 1959 Parts Catalog writer got creative with model descriptions. Then in the 1963 and later parts books, the 18508-52 became the -52A (the difference is currently unknown), and the fit of the 18523-57 becomes confused.

Parts Book Part No. Fits Fits - Our Explanation
1957 18523-57 1957 XL 1957 XL
1959 18523-57 1957-1959 All Sportsters except H and CH 1957-58-59 XL (?)
18508-52 1953-KK, 1956-KHK,
1958-1959 Sportster H and CH
[see KK and KHK section]
1958 and 1959 XLH and XLCH
1963 - 1967 18523-57 1957 - XL 1957-1958-1959 XL (?)
18508-52A 1958 to * XLH, XLCH 1958 to * XLH and XLCH