The V8 Owners Forum -

We are now approaching the final assembly of my new 4.35 engine with the Buick 300 heads. The bottom end is now built and we are just at the stage of putting the heads together

One thing that has arisen is that the valve stem heights are different for the the inlet and exhausts by approx 60 thou, I believe ideally they should be the same height so as not to have different pre loads on the lifters.

The valves are the same length for inlet and exhaust so should they be different lengths or is it normal to machine the seats and or valve tips to achieve the same valve tip heights?

Also anyone know whether the Buick heads need the short or the long reach sparkplugs, we put a long reach plug in to do a volume check and to my surprise it looked ok, I was assuming that the heads being of 1963 vintage would require short reach plugs.

Kevin.

hello

Is there any reason why you are called 'castle mgbv8'? Nothing to do with you having studied at University college, Durham is it?

I should have thought they would be the same height too, for the exact same reason. As far as my limited knowledge goes, the valve stems are the same length.

As for the buick heads and the short reach plugs. There's only, I think, the 11mm long reach and 24 mm reach isn't there? I may well be being thick here., can you not just measure the length of the thread?

If the stem heights differ by 60thou, that will give about 40thou variation on the tappet heights, which although in spec would be very hard to ensure that they are all in spec.

Adjustable pushrods would allow you to retrieve the situation.

Chris.

adjustable push rods is your answer. You better also check your valve spring installed heights as 60 thou is a lot. You use hardened shims under the springs to bring it into spec. Your rocker angle will be out as well but to be honest I don't know the effect of that.

Thanks guys,

Had a meeting with the engine builder this morning and he is going to cut the seats for the big valves with a view to getting the stem heights as equal as possible.

I am not particularly keen to use adjustable pushrods, so intend to measure the required lenght of a solid pushrod to obtain hopefully an average of around 30thou preload on the lifters. I spoke to Real Steal yesterday and they build there own engines with solid pushrods from a tube and end kit. Strangely they do not normally offer this to customers, but having spent quite a bit with them recently they said they would sell me the tube and ends so we can make them to measure.

ppyvabw. No connection with Durham University I'm afraid, I have a company called Castle Blinds and just used castle to create adifferent user name to the the other MGBV8 guys, and yes I will measre the threads for the plugs, NGK do a small range in short reach so shoudn't be a problem.

I'll post some pics of the engine build later.

Kevin.

If all the valves are of the same height but the tappet preload is still wrong, the normal way is to shim the rocker shaft pedestals.

Chris

Chris,

I know that shims are commonly used to achieve a desired preload, but by doing so it throws out the rocker geometry even further as the rocker tip is in the wrong position, as it moves across the top of the valve.

This causes premature rocker and valve guide wear as the rocker is working outside of it's original design criteria.

With the lift of the cam I'm using .488" I should be machining at least 30thou off of the pedestals to maintain geometry so the pushrods need to be shorter by that amount in addition after taking into account the rocker ratio of 1.6/1

Kevin.

I used shims on my first rover build when I was young and naive I made my own though because I wasn't forking out 25 quid for a few bits of tin, most of which would go in the bin.

My next one, I wont use shims for that very reason about the rocker geometry. I will either use the adjustable pushrods, or those ones with the balls you stick in the end then you get them made up to the correct length.

When I did my first rebuild, I think there was quite a discrepancy between the preloads, I think some of them were 20tho and the other end of the head were bordering towards 60. I phoned someone to ask about it, I think it was RPI, and they just said 'meh....as long as the pushrod doesn't become unloaded and loose, or the piston thing in the tappet isn't pushed to far in, then it's ok.

There's a lot of people who will say don't worry it will be ok, but if you want to do it properly Des Hamills book give some very good information.

Kevin.

Im working on memory here with Long reach plugs. I think I am correct in saying the old prefered plug for the RV8 used to be the N9Y, which was also the same plug used in about 90% of 60 british cars, so I dont see it being unreasonable the Buick will use an equvilent to the N9Y

Kevin,

Which valves did you use in your Buick 300 heads ?

I know an guy in USA who used :
for intake : 1.720" diameter piece from the 1988 - 92 Pontiac "Iron Duke" 151ci 4-cylinder engine (Federal Mogul p/n V2530)
for exhaust : 1.496'' Manley P/N11659-4 Volkswagen stainless steel intake valves.

Myseld I used Ferrea Buick V6 Stage II 1.775'' IN / 1.5'' EX.

CastleMGBV8 wrote:There's a lot of people who will say don't worry it will be ok, but if you want to do it properly Des Hamills book give some very good information.

Kevin.

I used Des Hamills book when building my 4.6 lump. I took the books advice and had 1.5mm removed from the heads where the rocker shaft pedestals are bolted down. The machinist commented that the location points are not parallel with the head gasket face. The book put me off shims.

If you look at the pad on the end of a rocker you can see that even the standard setup is not that good, the wear pattern shows a nice line contact at zero lift but vertually a point contact at full lift.

I did use adjustable pushrods from real steel and have found them to be OK. I have set each pre-load to 20 thou.

As I have had about 70 thou skimmed off the 3.5 heads (10:1 CR)combined with the lower rocker shafts I had to get all the pushrods shortened by 4mm. This is not hard to do as long as you don't fit the ball ends first!

If you do go for these pushrods and do need to shorten them beware that there is a small internal step that will need to be drilled deeper so that the ball ends seat properly.

I also had to enlarge the pushrod holes in the heads at either end of each head.

HTH,

Pete

Pete,

Thanks for the response, yes with the Crower 50232 cam which has approx .488" lift we will have to be carefull to get the geometry correct, my engine has 40thou off the decks and 25thou off the heads to get the compression ratio to the figure required.

I did buy a set of modular 5/16" pushrods thinking you could just pull them apart and shorteb them but the ends are somehow welded in and you cant get them apart without wrecking them so will hope fully get a kit from real steel. I've already opened up the pushrod holes for the thicker pushrods and we hope to have it all together next week.

Kevin.

CastleMGBV8 wrote:Pete,

Thanks for the response, yes with the Crower 50232 cam which has approx .488" lift we will have to be carefull to get the geometry correct, my engine has 40thou off the decks and 25thou off the heads to get the compression ratio to the figure required.

I did buy a set of modular 5/16" pushrods thinking you could just pull them apart and shorteb them but the ends are somehow welded in and you cant get them apart without wrecking them so will hope fully get a kit from real steel. I've already opened up the pushrod holes for the thicker pushrods and we hope to have it all together next week.

Kevin.

Hi Kevin,

The Realsteel jobbies are supplied with the ball ends in a bag so that will suit you. They are about 120 quid which is not peanuts but if you want it all spot on then you've got to cough up for the bits!

The skimmings of the heads and decks sounds like more than enough to give you bad geometry! "Des" does not recommend skimming the rocker pedestals but if I was you I'd think about getting it done. (I'm assuming that your heads are now fitted to the block). I'm sure that a decent machine shop could do it with the required accuracy.

I reckon that you may well need to get the pushrods shortened but that should not cost much. (If you have access to a lathe you could easily do it yourself).

I found in the end I could set the clearance pretty quickly once I worked out that once all the play was out of the pushrods a turn of "three flats of the bolt" would give 20 thou preload. It also helps to have 3 open ended spanners of the right size. (can't rember what the size is!)

Good luck and keep us posted!

Pete

A useful and inexpensive tool to have here is a pushrod length checker. Basically just an adjustable pushrod with a large range to it, it can make life much more simple when doing this kind of work. I got two from summit racing for about $10 each that between them cover anything from about 7-9.5" - enough to cover most pushrod v8 builds. I guess you could just as easily make the tool yourself though.