The V8 Owners Forum -

hello all,

Beginning to wish I never bothered with my latest 4.6 v8 engine build.

So got over a problem with piston rings & gaps....as per a previous post...

built the block up, and just checking for head gasket thickness, and that the valve cutouts that I had put in my pistons where ok.

what do I find.......the inlet valve is still fouling the piston.....and not going inside the valve cutout......so I still only have 1.5mm of valve to piston clearance.

As my inlet valves are 43mm and exhaust are 37mm.....it looks like chesmans have used the same size cutter to do both valve cutouts....., and yes I did tell them the size of each valve before they started.....

So I've now spent £670 getting valve cutouts and a full re-balance......but what do I do next?

1. just grind a small piece of each piston away so the inlet valve clears......but what will this do to the engine balance?

2. ring up chesman's and blow my lid......as looks like its their fault.....This would mean taking my block apart, taking it all back to them a 200 mile journey.....removing pistons from rods again.......and then re-balancing it all again.....

And not to mention 8wks wait for the work to be completed and the additional costs of gaskets, bolts a consumables which probably amount to over £100 I've just wasted.....

Disappointed is understatement at the moment......

any help appreciated.....

thanks

scott

Sounds like a chat with Chesmans is required to me.

Chris.

anyone got any ideas why the valve cutouts would not line up with the valves?

unless maybe they had been cut in the wrong place?

Its one of those hard things to check.

Off to find some modelling clay, to see how far they are out.

regards

scott

I assembled mine with checker springs,
put plasticine on the crowns assembled the engine then at tdc pushed down on the two valves that had checker springs fitted so the valves made a mark and had mine cut to the plasticine marks,

Sure the valve timing is correct ?

And are the pistons not intended for that engine ? ie valve cutouts would already be in correct location ( even if not correct diameter for larger valves ) ?

If Chesman did the valve cut out pockets then they should be on on the centred on the valves provided you have standard heads and not heads with offset valves.
I can't see how they would get things wrong if they had all the info re valve sizes etc.
They would have done the cut outs the same for both valves to allow pistons to be put in pots 2468 or 1357 but not side to side on a 4.6.

Sorry to ask this one but I assume you have assembled the pistons with the cutouts nearest the valley.

Good photo's save an awful lot of speculation.

I've now got some blue playdoh....as couldn't get any plastercine....but I think it will do.

Before I took all the pistons & internals to chesmans, I measured the valve clearances with no piston pockets, and I had only 1.5mm on the inlet.....

now its all back together with pocketed pistons, I still only have 1.5mm of clearance between inlet valve & piston, and there a slight marks just above the top of the piston pocket where it looks like the valve is catching the cutout, yet the exhaust valve now as over 4-5mm clearance.

I've got some radius gauges from work to check the actual piston pocket radius size, and I'm hoping this is bigger that the valve size of 43mm.

I cant believe they have got it wrong either, as its going to cost me an awful work of extra work.

Will do some more checks at the weekend, before I decide to take this any further.

cheers all

scott

when are you checking mate?
I was told 5-10 before tdc and same after is the most common place for piston to valve contact and it was correct on mine contact 10btc

Seight-V8 wrote:I've now got some blue playdoh....as couldn't get any plastercine....but I think it will do.

scott

Plasticine is for imperial 2v engines and Playdoh is for metric 4v engines.

scott[/quote]
Plasticine is for imperial 2v engines and Playdoh is for metric 4v engines.
[/quote]

Heh Heh Heh!

all,

so today I've spent a few hours trying to work out what happened.

Using the playdoh on the pistons, and tappets with 0 lash, and turning the engine over completely twice, it shows this.




not bad I thought....

cutting the playdoh through the exhaust valve, shows its inline with the piston pocket and about has 5.6mm of clearance.....good as per this photo.



cutting the playdoh through the inlet valve, looks like its really close to the top of the piston, and offset to the valve cutout, so the piston cutout is useless, as per this photo.



Measuring both piston pockets with some radius gauges, I find them at 22mm radius, so 44mm diameter, my inlet valves are 43mm and exhaust 37mm, so the size is good, as per this photo.



When you view the valve imprints for this view, its shows that the inlet side (right hand side valve) cutouts are not correct.



So what now, i've spent £220 getting the pistons pocketed, and £450 getting it all re-balanced, and £100 in bolts, gaskets & consumables.

That's now £770 pounds to find out I have no more clearance that I started with.......not to mention 3 months wait for the work.

My worry is now taking it all back apart and back to chesmans, which have already said my pistons, pins & rods are on the limit of size and probably will be too loose to do again!!!!!!!, which would mean, new rods or sleeves and circlips on the pins.....more work I don't feel like paying for.

Sorry for the rant, but after spending 5.5k on this rebuild, and supplying all the information needed, there is no excuse for this happening.

Rant over, and suggestions welcome and what to do next.

cheers

scott

Looks to me like they've not had the pistons lined up correctly on the mill before cutting the pockets, or they've got the valve centre line wrong.

I cut the pockets on Tony's pistons and the valve pockets just broke out the circumference of the piston. Acknowledged that the heads are TA so the valves are mahoosive and I did cut them 50.4mm diameter.

While annoying to have to machine the pistons again...surely it's a very easy job to do so ? And can they not do it without moving the road ?

or...although messy. DIY. Get a larger valve and fire away.

http://www.homemadetools.net/homemade-piston-flycutter

But could be done without removing the pistons.


For all the material that would be removed, I wouldnt be overly worried about it affecting balance. etc.

yes I'm thinking that I might need to remove 1mm at most at the inner edge of the piston cutout of the inlet valve by hand maybe, don't know how much weight I would actually remove, and how this work affect the engine balance, if I try to get them all the same on each piston.

I'm not sure it can be fixed any other way than engine apart again otherwise.

Unless I went back to heads with smaller valves.

its a headache, but I think I will ring andy at chesmans on Friday first and see what he thinks, before I do anything major.

regards

scott