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MG MGB Technical - Rocker gear spacers
Just fiddling about with a mate's rockers that had previosly been fitted with tubes instead of springs to hold the rockers in place. No problem there but one of the end tubes is .070" longer than the other.
I know they are supposed to be the same but - The problem is I can't find the measurement for the centre and end tubes, I have it somewhere but have put it away somewhere so that I won't loose it , as you do.
If anyone has the specs. and can let me know please-
|*Are* they supposed to be the same? Surely each should be just long enough to take up the space between rocker and pedestal where the spring would normally go. Measure those gaps and the tubes will be right for your engine. AFAIK tubes instead of springs is non-standard so you are hoping to find someone else that has done it to the same engine, and I've never heard of it before.|
|They used to be available 'off the shelf' for the A-series engine - presumably still are - but they usually had to be tailored to the engine they were being fitted to.|
Personally, I wouldn't worry about the individual lengths, as long as they are taking up the slack.
|Dave O'Neill 2|
The use of tubular steel spacers rather than the Original Equipment spring spacers is highly advisable when using a high lift camshaft that extends the powerband beyond 6,500 RPM in order to preclude longitudinal ‘walking’ of the rocker arms at such high engine speeds. However, the Original Equipment rocker arm spacer springs (BMC Part # 6K 871) are quite adequate for this task at engine speeds below 6,500 RPM and have the dual advantage of less friction as well as damping valvetrain vibration and its resultant noise. Tubular steel rocker arm spacers are normally found only on race engines, but their omission in a street engine that is intended to be operated at higher than normal engine speeds can be a mistake. Because a race engine is torn down and carefully inspected quite often, there is no problem with crud accumulating inside of the tubular steel rocker arm spacers as well as between their shims and the rocker arms. The factory used spring spacers as Original Equipment partly because of their quiet operation and partly in order to allow crud to be washed free from the rocker shaft. Due to their potential for inducing rapid wear on the side faces of the rocker arms and the rocker shaft pedestals should their shims wear through before being replaced, they are rarely found on a street engine. Their .004” +/- .001” (.1016mm +/- .0254mm) gapping should be checked with a Plastigauge every time that the valves are adjusted in order to monitor for this eventuality.
Thanks but they have two part no.s one for the centre and one for the ends.
The posts can move a tiddle to get correct clearances
I've used spacers on my own stuff for years but my current engine has offset rockers etc so can't measure off that and I don't have the head from this engine at the moment so can't mount the rockers and measure
It may well be fine as is but I guess I'll dig into the cupboard and see if I can find a soec.
Have a Happy and Safe Christmass all---
Can't find it
Moss do a set - anyone got the measurements
I wouldn't worry but I have a piece of hi.mod carbonfibre tube just the right size and am desperate to use it and would really like to get the correct measurement just to make it all proper like so that when it's pulled down by someone else in the future it's all good - It's only my own pride I guess that is stopping me leaving it as it is.
The specs would really help if one of you have them
|Longer one goes in the middle, but would normally be adjusted, and shimmed to get rockers dead central. I rocker, cannot remember which, probably No 4 inlet will never line up unless you machine the pedestal. So shims are needed to do final adjustments. Race use only. Springs fine for the road.|
Dont think I would use the C/F tube. It will wear.
It is quite obvios the long one goes in the middle
I'm after the standard length for the tubes - simple as that is it appears to be a secret
Wear of the tubes if I go carbon is not a problem as this thing gets a precautionary rebuild after every twenty hours use anyway , It's a very high tech. motor with alloy conrods and all the goodies
The standard lengths are all I'm after - Willy
|If the carbon fibre is wearing away, I would be concerned about where the bits are going.|
|Dave O'Neill 2|
It's Hi. mod carbon -- Believe me it's not going to wear
Nylatron bushes are available and if that will do the job c.f. will be fine and it will be checked regularly anyway so if by chance there is a problem it will be found early.
Does anyone have the lengths please , that's all I am asking
|There isn't any standard length. It's a non standard part, and is normally fitted to the space available, once you decide where you think the rockers need to be relative to the valves. You must account for any possible position variation of the stands, wear on rockers and stands, other thrust washers etc. Then measure the spaces and subtract a reasonable clearance, like .005, then machine to fit. If you buy off-shelf items, they will either be too short and loose and need shims, or too long then you get to machine them anyway. Presumably this was done and is why you have one different.|
|OK - Thanks guys - the lathe is spinning. I'll make a set the same length as the old ones and when I pick the head up tonight it should be a simple bolt together job.|
I must be catching something off Prop, I wanted it to be harder than this.
The old ones are fine really but these will look specy when we're doing the tappets between runs. Just an extra little something different to keep the opposition worried, every little bit of bluff helps
|Willy you will need to adjust each tube to suit, and bear in mind my point about machining one of the pedestals as 1 rocker nevr lines up|
The problem turned out to be one of the previous fiddlers with this engine had machined the side off one of the posts or so I thought. Presumably to try and get everything where it should be. ???
Anyway I found another set, luckily, that a mate had and fitted the shaft and rockers to them and bolted it all to the head and it lined up great.
Spacers ended up.------
Centre -- 1.275"
Outers -- 1.250" X 2
On further examination of the dud rocker post it does in fact measure the same overall width as the others so hadn't been machined at all, the problem is that the holes down through it for the headstud and rocker stud are about .060" off centre. How that could happen is beyond me but there you go. check check and recheck eh-
Thanks for your input Willy
This thread was discussed between 22/12/2010 and 25/12/2010
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