How to do a valve adjustment

Thanks to the help of several key LamboPower board members as well as many discussions with local performance auto mechanics, I'd like to summarize here the things I've learned about doing your own valve adjustment. Typically, this should save you about $2-3k, depending on your dealership.

 

Background (most folks can skip this)

Valves control when a cylinder in an engine gets intake (air/gas) and releases exhaust. In Lambos, valves are opened and closed mechanically by four rotating camshafts, each of which has tappets (egg-shaped bumps) that press against spacers sitting in buckets on top of the valve. So a valve opens when a tappet on a camshaft rotates to where it pushes against a spacer, which pushes against the bucket it sits in, which pushes a valve down into the cylinder. Over time, these mechanisms wear and distort such that the gap ("lash" or "clearance") between a tappet and its spacer changes from the factory spec. When this happens, valves begin to open/close too soon or too late, resulting in lost efficiency (at best) and burned valves (at worst -- or perhaps even worse can happen, I suppose). Lambo recommends adjusting your valves every 15k miles.

 

Intro

You can adjust your valves without removing the engine. It's a lot easier with the engine out, but it's definitely doable with the engine in. For your first time, a valve adjustment will likely take between 5-8 hours, depending on how mechanically inclined you are and also how carefully you do your work. Overall, the job isn't difficult.

 

The overall approach is simple:

1. Remove the valve covers
2. Measure existing clearances
3. Measure existing spacers
4. Do some simple subtraction to figure out what spacers you need
5. Install new spacers
6. Close everything up and drive away

None of it is difficult, though it can be time-consuming. You'd be amazed at how easy it is.

 

Materials

You'll mostly be working with simple hand tools that can be obtained from anywhere.

• Metric sockets. Most popularly, the 10mm, 13mm, and one 24mm for turning the engine.
• Socket extension bar, perhaps 12" long.
• Breaker bar for turning the engine.
• A set of metric tappet feeler gauges (about $5).
• Paper, pencil, and perhaps a little tape to mark stuff
• A valve adjustment tool. You could spend $220 and buy one. You could rent one for $22/wk. Or you could make one for $4 like I described here.
• A nifty Valve Adjustment Guide, which I created and provide here: Diablo_Valve_Adjustment.pdf
• (Optional) A spreadsheet to help double-check your math, which I've hosted on Google Docs here.

Removing the Intake Manifold

This part might be fairly obvious, so I'll be brief. You'll want to lift off the entire intake manifold by unplugging everything from it and taking it off the engine. Detach the intake hoses that come from the air filter; detach fuel lines; unhook electricals (I'd recommend marking them unless you've got a great memory); unscrew the throttle linkage. Lift it off the engine with a friend -- it's not heavy, but it's a bit bulky, especially if your engine is still in the car. More details here.

 

Remove the Valve Covers

I've also described this in a previous thread, so please see more details there.

 

Measure Clearances

Use a set of metric tappet feeler gauges to measure the clearances between your tappets and the spacer disks below them. Do this when the engine is cold (that's important -- things expand and change when the engine heats up). Use tappet feeler gauges, not regular flat feeler gauges. Tappet feeler gauges have a bend in them that make them easier to slide under the tappets. The right measurement is where the gauge slips in without much force and glides around, but clearly contacts both the tappet and the spacer snugly.

 

You should measure the gaps only when tappets are facing up so that they are at their maximum gap with the spacer below. You'll be working on a pair of tappets and spacers at a time, cranking the engine once in a while to expose new pairs of tappets to work on.

 

 

Record the gaps, perhaps in the Valve Adjustment Guide I've uploaded above. Next, remove the spacers under the tappets you've just measured by inserting a valve adjustment tool (described above and in this other post) between the pair of spacers. Measure and record the thickness of each spacer by using digital calipers. You could alternatively rely on the spacer's label ("3-80" means 3.8mm), but that requires some faith that the spacer hasn't itself worn down through heavy use. You need to measure the spacers' thickness so that you can derive what thickness of spacer you need in order to achieve the ideal clearance.

 

 

Once you've done all the pairs of tappets that are facing up, you'll need to turn the engine a bit in order to get other pairs of tappets in the correct position. You can either turn the engine from the flywheel side by using the $600 Lambo tool, or alternatively use a 24mm socket on the crankshaft bolt, pictured below.

 

 

Note that you should only ever turn the flywheel clockwise, or the crankshaft bolt counterclockwise. This is very important. Seriously -- you could mess up your timings. Double-check yourself before turning anything.

 

And loosen your spark plugs, if you haven't taken the opportunity to replace them. This will allow air to enter the cylinders when you turn the engine and greatly simplify the job. And be in neutral.

 

Using a breaker bar and and a 24mm socket, you should be able to easily turn the engine. Work on new pairs of tappets until you've measured all clearances and all spacer thicknesses.

 

Getting New Spacers

You can do some simple math to figure out the new spacers you need, or alternatively use the spreadsheet I uploaded above (in the Materials section) to help double-check your math. The spacers are 29mm wide, which is a size that almost nobody local will carry (but do let me know if you find compatible ones). Lambo will sell you most spacers for $6-8 each. But -- and here's the reason you've gotta love 'em -- every once in a while, a spacer will be $40. Like 3.70mm. Why, you ask? Because those are the most popular spacers. Nothing like a little blatant gouging to show some love for its customers.

 

You can also get a local machine shop to use a surface grinder to reduce a thicker spacer to a thinner one. This will take an expert machinist perhaps 5 minutes a piece to do a really careful job. And you want a careful job -- you do NOT want spacers that are crooked.

 

I ended up buying most of my spacers, and getting a machinist at a performance auto shop with 30 years of experience to do the 3.70mm ones. He did a great job.

 

Insert Spacers

Replace the right spacers with new ones you've gotten by using the valve adjustment tool to lower the buckets and then setting each spacer firmly in its bucket. I'd recommend setting the spacers with their label-side down so that you'll have some idea what you put in when you do your next valve adjustment.

 

Check your clearances to make sure you've done a good job. Congratulate yourself.

 

Drive Away

You'll need to put the valve covers back on (with new gaskets), tighten your spark plugs, and install the intake manifold (using new gaskets as well -- I'd recommend Viton ones).

 

If you have specific questions, or suggestions of things to add to this guide, please let me know and I'll edit this post to incorporate your contributions! Thanks, everyone, for your help and support.

You have done it again. Thank you for your effort to making Diablo ownership a little more simple. This kind of information will become usefull for all enthusiast owners at some point!

I think it's pretty clear you we're pulling our legs that the only prior experience you'd had was replacing the timing belt on a Honda. Come clean now. Your a factory trained technician right?

Thank you for the excelent write up.

Your da man

FiveCar,

 

It's very refreshing to see another owner working on their car. You really are what this hobby needs. I wish you the best in your current endeavor. Not that you need it.

 

Best

FiveCar thanks again for the write-up. Superb. You need your LamboOwner's title now too.

FiveCar thanks again for the write-up. Superb. You need your LamboOwner's title now too.

Hehe. I figure if I keep up the good work, I might weasel my way into honorary VIP status through shameless brown-nosing.

Great stuff Phil, coming along nicely

:icon_super:

Incredibly impressive! Great work!!