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RB26 Valve Clearance

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I just replaced the valve springs in my RB26 (I did not measure valve clearance before disassembly - failure on my part). This engine has been running the Greddy EZCam 264-9.1 cams reliably since before I purchased the car in 2012. The FSM calls for IN 0.45 EX 0.38 and the specs from Greddy say there is no need for valve clearance adjustment from FSM specs. After reinstalling the shims/buckets and cams into their original locations I measured the following values: IN 0.30 to 0.33 and EX 0.35 to 0.38.

After searching for many hours, I have found that similar HKS and Jun 264 cams call for IN 0.30 EX 0.33 and Kelford 264s call for IN 0.25 EX 0.30.

Would my current measured values be acceptable because other brands are also running a much tighter intake clearance or should I disassemble the whole thing and order shims to meet the FSM specs?

I'm certain I know what the "right answer" is but I also have not found clear guidance saying that my measured spec is NOT acceptable to run.

With the exhaust specs being correct and all the shims measuring pretty even across the board I find it hard to believe these were not originally purposely shimmed tight when the cams were installed probably 15+ years ago. Just looking for a sanity check before I commit to tearing it all apart and starting over.

Unless the camshafts are ground by the same company and/or profiles, it is unlikely they will use the same lobe shape or, MOST important, clearance/take-up ramps. These are used to smoothly transition the followers to the main profile without any high impact loads - think of it as being like the difference between putting your fist against a hanging weight and pushing it vs just punching it from a few inches distance.

You may be OK with what you're running, and personally I'd probably run it while arranging to have the shims set - but I would recommend using the manufacturer/supplier's specified clearances*, as they are an important part of the over-all camshaft's performance characteristics. For the most part, the exhaust is more important, as the time on the seat is used to pull a lot of heat out of the head.

IMO, it's always bad practice to re-use followers on a new camshaft, even with copious amounts of anti-scuff lubricants, and especially mix them up on old camshafts - did you use new ones?

It's a little difficult to read if your supplier was suggesting you could just drop in the new cam's on the old shim sets, or just to use the OEM clearances?

*prioritise the manufacturer's/grinder's, as they should know the specifics and, even with the best, sometimes retailers 'fudge' the facts to simplify things for the potential buyer. It's also not uncommon for the same grinder to provide identical grinds to different companies who re-package them for sale - nothing untoward, if done properly.

Oh, the only way clearances can close up is if the seats/valves wear, the seat in the head is ressessing and/or the vlave head is deforming (tuliping) - none of these would be expected to be significant on modern engines unless very high mileages are completed.

I appreciate your thoughtful reply! I'll add a little extra context. These cams, followers, and shims were installed by a previous owner, pre-2012. I only removed them to replace the valve seals and heavier valve springs. When I removed them, I ensured each follower and shim was labeled so it could go back to its exact location. My failure was not measuring the pre-removal clearances for future reference. After replacing the valve seal and new springs, I replaced the shim and follower to their prior location and then installed the cams; so none of these parts were "new".

As for supplier recommendations. The Greddy site (both English and Japanese versions) are very vague compared to other cam suppliers. The English page says "Drop in, no need for valve timing adjustment or cylinder head clearance." and the Japanese page gives a chart with the duration (264*), lift (9.1mm), valve timing (110*), base circle (32mm), and valve clearance (STD).

With the exhaust measurements being right on what the FSM calls for, I'm under the assumption that whoever originally installed these cams shimmed the intake tight and the car ran for years just fine. But I'm not sure how much faith I want to put into that assumption lol. As I said above, I know the "right answer" is to probably take it all apart and shim it to FSM specs. Was just hoping maybe someone else with some RB knowledge would chime in with a "running them tight is fine" comment.

Appreciate the support!

Sorry, me bad - completely missed the bit about how long they'd been in.

I also missed reminding you that this was MY thoughts, and it is a very good idea to get others' opinions who are experienced with that specific platform.

Personally, as they've been in so long without isse, and it's a lot more common for them to open slightly, I'd leave them as-is. If you can 100% confirm the camshafts' make and spec', you could go through the hassle and expense - it's set your mind at ease, anyway. Oh, sometimes clearances and/or cam' grinds change slightly, so if you can check what the spec' for clearances was at the time.

Have you tried the RB forums, they should be able to better inform you.

I run the Kelford 264s with the clearance they recommend without any problems.

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