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Cam compatability - 4.0/4.6 blocks


FridgeFreezer

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I'm hoping someone can answer this - I have a 4.6 with after-market RP4 cam & duplex chain which currently has an early style front cover, and I've got the proper P38 front cover & ancillaries to fit to it. However, I've seen several posts mentioning that most after-market cams won't work with 4.x engines.

As I'm running megasquirt I don't need distributor drive *or* a camshaft sensor so as long as the cam physically fits in the housing it doesn't matter to me, so the question is - will my existing (dizzy-type) cam fit inside a P38 front cover or am I going to have to pull it out?

Everything online is aimed at standard vehicles, so it's always a cam kit with different timing gear to suit the cam sensor / dizzy, but no definitive photos/info on what the difference really is or if it matters.

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I believe the problem is the timing case is shallower, and won't support/have enough room for a duplex chain. The best you can do is go OEM for timing chain and sprockets, and that of course makes your current cam redundant.... as the timing sprockets are different. Also, if you don't have it, you should have a retaining plate holding the cam if you don't run a dizzy, older style cam shafts do not have the groove in the camshaft end to support this, though many suppliers will do it if asked, and you want to fit a multi-V front end on a serp block.

Nige may be along to say the 3.9 serp cover is deeper, but then you still have a hole for the dizzy...

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Thanks Bowie, looks like a new cam too then, that puts the job back a bit :(

3.9 is an option I don't really want to go for as I'm trying to get the engine to be using all standard parts from the same model of vehicle as far as possible, it's a mongrel at the moment and it causes headaches with parts.

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If it's too shallow, why not fit a spacer plate with 2 timing cover gaskets?

I know the obvious answer is that the serps oil pump won't drive right, but it's going to depend how much more room is needed for the duplex chain and how far the pump and front pulley can be tweeked forward.

Or the lack of chain space might mean some case welding, but it is weldable.

Don't get me wrong on this, I havn't seen one and don't know the exact issues :)

(But I have created some unlikely amalgamations by a bit of sideways thinking)

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I think FF wants standard parts ;)

You'd have to do something with the crank pulley as well, they are pretty short on this engine.

FF, one other thing, if you're not running a remote oil filter you may need to... the P38a setup plonks it in a totally different place -I clouted mine with the diff pumpkin before realising :blush: I know you are on portals but the same may apply, as IIRC you had the axles in the same place as stock.

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Extending the timing case would mean extending the sump too, that's a recipe for lots of work and a leaky engine, I'd rather just stump up for a new cam TBH!

Good point Bowie, I'll be waving the tape measure at it before I go very far with it anyway.

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Its not just "The Blocks"

Its the cam type, the crank type, the cam fixing stylee and the timing cover / gear asembly

On the 4.0 their are Motronic and GEMS covers and tinming assemblies, you can swap ENTIRE assemblies over, but that includes the timing cover

gears chain and all the ancillaries as things like alternators pas pump belts tensioners all vary.

The crank is importnat as the length is different (longer) on a serp than a V belt, there is a oddball 4.0 crank that is between the 2, but a 4.6 should have a

longer crank, and you should be able to fit a 3.9 front end or a 4.6 of a 4.0 assembly, as the cams have similar mountings BUT differing gears and chains. The 4.0 flavour

can't have a HD chain assembly as the gear is unique to it.

Some pics of what you have and what you wnat to fit would help, its a buggers muddle doing this, do not try to mix parts from timing covers and ancillaries !

Whatever cover you use make sure you have all the ancillaries for that cover :(

Tried to help here, but your head is prob spinning even more :lol: oh and to finish sumps are different too, as can be the pick up pipes !

Nige

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  • 3 weeks later...

Just had a fairly definitive answer from Kent Cams:

- Any cam they make can be made long-nose (3.5, 3.9, 4.2) or short-nose (4.0, 4.6), you need to specify when ordering.

- Duplex timing chains will NOT fit behind the 4.0/4.6 front cover

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  • 4 weeks later...

CHeers Fridge, nice to get some definitive info :)

Mine is a Kent cam too, H200 IIRC, couldn't go much wilder with the autobox, but you could go silly with it if you really wanted as you're manual ;)

What is the reason you can't go wilder with the autobox? and what do you mean by wilder? more peaky/power at top RPM?

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With a wilder camshaft, idle speed often has to be raised to remove the lumpiness caused by the cam, as an auto box torque converter is designed to work at a specific idle RPM you start getting too much creep.

1000rpm idle and auto = creeping with brakes on in low first = bad!

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