valve to piston clearance - checking

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Seight-V8
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valve to piston clearance - checking

Post by Seight-V8 »

hello all,

Looking for the method of checking the clearances between the valve and the pistons.....on the rover v8

I'm sure I read on here.....but cant find it through the search function.

Anyone point me in the right direction or can describe what involved.

Just trying to work out if my pistons need pocketing before I fully assemble the block.

cheers

scott



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Post by sidecar »

Its not too hard to do but you need to obtain a few bits and bobs first! Well done for checking, many people don't bother and I think that the result is a right old bodge of a build unless you are sticking with standard components in which case it is fine not to check.

You need two followers which you need to take apart, clean up then fill up with glue or wax or something before rebuilding them, old followers are fine to use. It is important that they are solid, the inner cup must not be able to move.

You need two adjustable pushrods, if you are handy with tools you can make a set using old standard pushrods.

You need two weak checker springs, you can cut an old spring in half from an old rocker gear shaft, they will work well.

Dry build the engine, fit the two weak springs to the valves that you are going to check, fit the followers and make sure that they are on the base circle of the cam. Fit the pushrods and adjust them so that there is no play in the valve train but at the same time the valves must not be held off their seats. The critical crank angles are from around 15 degrees BTDC to 15 ATDC at the end of the exhaust stoke/start of the inlet stroke.

Place the crank at 15 BTDC, the valves should be on the rock, i.e the exhaust closing and the inlet opening. Push down on each rocker at the point where the rocker bears down on the valve, if the valve moves a long way and does not hit anything then you are OK for this crank angle. Turn the crank 5 degrees to 10 BTDC and test the valves again. Repeat the process until you are at 15 ATDC. If at any point you can feel a valve hit a piston and you want to know what the clearance is push feeler gauges between the valve stem and the pad on the rocker, if you can get a 1mm gauge in and no more then the clearance is 1mm!

Don't let anyone fool you with crap about the follower pre-load effecting any of this stuff, it doesn't! The cam lifts the valve X amount regardless of the preload on the follower! The minimum figures escape me for the clearances but a quick google will find them. It might be 1.5mm in the inlets and 2.5mm on the exhausts. The exhaust need a higher figure because they are on the negative side of the cam, this means that they could have 'floated' off the cam and therefore be open more than they should be. It is impossible for the inlets to be in this state because they are being forced open, there is no way they can float at the crank angles we are concerned with.
Last edited by sidecar on Sun Sep 04, 2016 12:53 pm, edited 2 times in total.

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Seight-V8
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Post by Seight-V8 »

cheers sidecar.

seems like a really good and quick way of checking the clearances.

think I have most of these things somewhere in my garage.....

Shouldn't take too long to check the clearances.

thanks

scott

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Post by sidecar »

No probs! I've just thought of a couple of other things! You need an old head gasket or failing that you can use some aluminium strips that are the same thickness as a compressed gasket.

Also you can check the valve spring retainer to valve guide oil seal whilst the engine is dry built. Just turn the engine over until each valve is at peak lift, then try pushing the valve down until the spring keeper hits the oil seal. I think you need a couple of mm clearance. If you do not have this (or any clearance) the valve guides will need to work!

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Post by SimpleSimon »

I have nothing to add to Sidecars good post, other than I used cut down rocker shaft springs for my valve checker springs :wink: heavy enough to close the valve but light enough to get feeler blades under inc finger pressure the rocker to measure VTP clearance if things are getting marginal
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Post by Coops »

awesome I was going to buy checker springs but I'll now cut down the springs from my old rover rocker arms, cheers guys 8)
Regards Tony C (COOPS)
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Post by SimpleSimon »

Coops wrote:awesome I was going to buy checker springs but I'll now cut down the springs from my old rover rocker arms, cheers guys 8)
Glad it was of use I also commented on your build on FB Tony 8-) its a small world :lol:
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Post by Coops »

sure is mate :lol:
Regards Tony C (COOPS)
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MS2 V3.57 Ecu mapable efi and wasted spark ignition.
Procharger D1SC supercharger and Cossie RS500 Intercooler @ 14psi of Boost. 416 RWHP, (boost leak)
Forged 4.8 V8 kitted out with the dogs Cajones of parts. :D
Sponsored by: www.v8performanceparts.co.uk, www.interpart.biz, www.caprisport.com & www.baileyperformance.co.uk

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Post by Seight-V8 »

done my checks with a dial gauge, and looks like l have the clearances below.

inlet 1.34mm
exhaust 2.51mm

So looks like a job to pocket the pistons, next time I'm in Coventry, and back to chesmans.

Luckily at the end of this month.

Anyone got a ball park cost for this before I ring them?

cheers

scott

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Post by sidecar »

Seight-V8 wrote:done my checks with a dial gauge, and looks like l have the clearances below.

inlet 1.34mm
exhaust 2.51mm

So looks like a job to pocket the pistons, next time I'm in Coventry, and back to chesmans.

Luckily at the end of this month.

Anyone got a ball park cost for this before I ring them?

cheers

scott
You might just about get away with those figures but it would be worth doing some research as I may well be wrong!

I did cut eye browse in a get of pistons using some old valves that I turned into cutters, I increased the diameter of the valves first by building them up with weld. I would not recommend this method as it was hard work and the cutters only just lasted long enough to do the job. You can buy proper tools to do the job but they will probably cost as much as getting someone who is setup for this sort of stuff to get them for you.

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