3.5 to 4.0

[stu e]

I currently have a 3.5 RV8 in my car and am thinking of upsizing the engine.
I've seen a couple of 4.0 litre short engines for sale and was wondering if I could use my existing heads, timing cover, oil pump etc to make a complete engin? Or would i be better off looking for a 3.9, and if so would i notice the difference from my 3.5?
Any thoughts.
Stu.

[Sidecarbod]

Originally Posted by stu e

I currently have a 3.5 RV8 in my car and am thinking of upsizing the engine.
I've seen a couple of 4.0 litre short engines for sale and was wondering if I could use my existing heads, timing cover, oil pump etc to make a complete engin? Or would i be better off looking for a 3.9, and if so would i notice the difference from my 3.5?
Any thoughts.
Stu.

I did something similar a few months ago but went to 4.6 litres.

I beileve that the factory did not build any 4.6 engines that use the the 3.5 timing cover and other stuff but it does all work very well.

I was told that it was just a bolt together conversion and I guess the motor would have run if I'd just bunged it all together. However I wanted to get the best out of my new engine so it ended up needing quite a bit of machining to get things like the CR right, the right length pushrods, the right valve train geometry. etc. None of this stuff is hard to sort out.

My 4.6 goes like hot snot IMHO !

Ive heard that the improvement from 3.5 to 4.0 is still very good, much better than you'd expect from just a 500cc increase in capacity.

What you need to be careful about is the cracked block, liner dropping issue. You won't spot a cracked block no matter how hard you look, You may spot a dropped liner. You should also read Des Hammills book, he explains in great depth which blocks had which issues.

If you are serious about doing the upgrade then I can give you more details on what I did.

Pete

[Sidecarbod]

Oh, one other thing, I wanted to use my 3.5 heads as they'd been gas flowed to stage III with large valves etc. I guess if you've just got standard heads then the value of using them deminishes somewhat.
Not that the heads off the bigger lumps are any better. They may have smaller combustion chambers but that's easily sorted out with a head skim. I'm assuming that you have an SD1 here, not a P6!

Pete

[demus]

Hello Stu,

I'm now doing a similar thing myself, but with a 4.6 bottom end. JE Developments are doing the work, the bottom end will be new, but my heads, front cover, valve gear etc etc will all be recon'd if necessary and on the "new" engine.
If you have been looking at new 4.0 short motors, there may not be a huge price difference to a 4.6.

[stu e]

Thanks for the replies.
Yes I have an SD1 engine not P6.
I've heard talk of spacers needed on the crank, i just wondered if it was do-able and if so how many mods would be needed to my stuff. Also if you can use an SD1 timing cover and oil pump as I need a remote oil filter. The other problem is if it makes the engine any longer, i'll have an issue with pulley clearance.
Cheers Stu.

[David Large]

Hi,

I had a new 4 litre built about 3 or 4 years ago; when I say new it was built off a new crossbolted and braced core of new block, crank, con rods and pistons. It has my old heads, re - worked, a fast road cam etc etc.

It is great. A 4.6 short engine would be the same price, I decided against it because I have an MGB underpinned 289 and I did not want to stress the MG bits too much, I was worried about carrying sufficient fuel for a 4.6 and also keeping it cool.

It produces 235 bhp and 250 ft lbs of torque.

David Ellis of Nuneaton built my engine for me and it is absolutely fine.

Good luck

[Sidecarbod]

Originally Posted by stu e

Thanks for the replies.
Yes I have an SD1 engine not P6.
I've heard talk of spacers needed on the crank, i just wondered if it was do-able and if so how many mods would be needed to my stuff. Also if you can use an SD1 timing cover and oil pump as I need a remote oil filter. The other problem is if it makes the engine any longer, i'll have an issue with pulley clearance.
Cheers Stu.

The spacer costs 7 quid!

Here goes, this is what I did, you may or may not have to do all this it really depends on what you want to end up with.

1. Buretted each and every combustion chamber then did the same with each piston at TDC then worked out the CR for each cylinder when using composite head gaskets. (For every 8 thou skimmed off the head the vol shrinks by 1cm3. This is NOT the same for a block skim due to the non-round shape of the chambers). In total 70 thou has been taken off my heads. 10:1 CR

2. As I am using a hi lft cam I had 1.5mm skimmed off the heads where the rocker pedestals sit. The pedestals could have been skimmed instead but "Des" reckons it better to do the heads. This is done to get the valve train geometry right. Using shims to get the preload right makes the geometry even worse and it isn't very good to start with! (Even with a standard cam).

3. The two outer pushrod holes at either end of each head had the be filed out as the pushrods that I was using were a bit to close for comfort.

4. Realsteel adjustable pushrods were used but due to all the machining they would have been too long, I had them all shortened by 4mm. There is a small internal step that also needs to be drilled out slightly deeper so the ball ends seat properly. I set the pre-load to 20 thou for each valve. This would be very hard to to with shims. (Pushrods are about 120 quid)

5. I have the performer manifold and had 40 thou machined off each face (not 70 as it still fitted when the heads had only 30 thou off them). I should have had the inlets on the heads done as it would have been loads cheaper. The manifold was a git to machine, apparently!

6. I fitted the camshaft retaining plate as the 3.5's method of camshaft walk is crap. This caused a issue as I have a piper vernier timing chain setup. The cam sprocket then fouled the bolts that hold the plate in place. In the end I ground the heads of the bolts until they were only about 1.5mm thick. RPI will sell you a plate which has been counter sunk thus avoiding the issue! Degreeing the cam in is a pain in the bum but if you are using standard stuff then you won't have mainly because there is no adjustement to be had!

7. I found out that the cam in my 3.5 was knackered so I bought a piper 285 and a new set of standard spec (but not Rover) followers. You need to be careful as there are a load dodgy standard followers on the market, they have been machined wrongly and colapse. RPI get theirs made in the US somewhere. If your cam is in good nick you can reuse it and the followers but you must keep all the bits in the right order. Take a long hard look at the cam, followers, rockers, and rocker shafts, the RV8 seems to eat this stuff! Personally I don't like any of the bleed down lifters.

8. The dowel that locates the flywheel on the back of the crank either needs to be pulled out of the crank or cut off. (5 mins with a hack saw, but cover everything up with tape and hover up the swarf). The 3.5 flywheel does not have the hole for the dowel but does not really need it as no timing is taken from the flywheel, unlike the standard larger lumps.

9. I fitted a TVR clutch from RPI, this cost about 200 but I can't quite remember, I also bought a new release bearing but I should not have bothered as the one from my 3.5 was fine. I also used longer bolts to hold the pressure plate in place, I then fitted nylocs that were also locited to the back of the flywheel. I then had to grind some of the block away to allow the thing to spin! Not sure why I bothered doing this but it seemed like a good idea at the time!

10. I had to remove the spigot bearing as my new short engine did not have one fitted, yours might. I did the old fill it with grease trick then tap a close fitting bar into the hole in the middle.

11. The front damper will fit but needs a spacer at the front to allow the bolt to tighten. 8V Tuner sells this and I guess RPI will too. whilst the damper was off I made a load more timing marks that were important to me. I used a junior hack saw blade, I sprayed the damper black then filled in the cuts with white paint. I also remade the pointer as the Rover one is a bit odd and not easy to take a reading from. The damper does NOT stick out any further than the 3.5 lump. Its hard to explain why but easy to see why when you have the bits in front of you. I did not have the damper fitted when I fitted the engine back into the car, I then could not get the damper back on as the longer crank ment that I just did not have the clearance. In the end I cut a small lump out of the chassis cross member!

12. Its up to you how far you want to go but I removed all the valves, i spun each one in my pillar drill and held up a drill bit against them, this nicely removed the carbon from the backs and the fronts of the valves, I then polished both sides of the valves up. Each valve was lapped into its seat. (New valve guides were fitted as I was worried about where the carbon on the back of the valves had come from)

13. Whist the valves were out I was annoyed to find that the stage III gas flow that I paid for was not that great just behind the valve seats, which is the bit that you can not see when you get your heads back from the tuning shop.

I used a load of tungsten burrs to blend out the step.
I've been told that 80% of the gain of any gas flow job is due to this area so you really should think about doing this. It was dead easy, you could use a dremel but you need very good burrs, not the crap that you get with the dremel. (you will still use about 8 of them!)

14. I fitted ARP head stud, they are the biz and make the standard stuff look very thin and spindley!

15. I did the drilling of the block mod to aid lubrication of the timing chain.

As far as I can remember the front cover and sump all fit without a problem as does the pickup etc. (I have a pickup kicking about and noticed that they can varry in length so don't just use any old one, it must uit the sump.

All of the above sounds like a load of work and it was! It was not hard to do, it just takes time to tripple check that everything is right. If you went for a 4.6 and had a good cam, rasied CR, home gas flow, good manifold and carb then you might get 265-285 BHP which is nice. The real killer is the low down torque, I can change up the gears with 1200 RPM showing on the rev counter, it will pull top gear from around 1400 rpm but this depend on the diff and box that you are using.

I've done some other stuff but that's a secret! You'll have a good motor if you do what I've listed above

HTH,

Pete

[stu e]

Cheers Pete
You have been busy!
I'm glad to hear it's all do-able and will look a little more closely for bits to collect.
I'd intended fitting a new cam and having some work done on my heads this year, but am seriously thinking about upsizing now.
Thanks for your info.
Stu

[Sidecarbod]

Originally Posted by stu e

Cheers Pete
You have been busy!
I'm glad to hear it's all do-able and will look a little more closely for bits to collect.
I'd intended fitting a new cam and having some work done on my heads this year, but am seriously thinking about upsizing now.
Thanks for your info.
Stu

No Problem Stu,

I'm not around after tomorrow evevning for two weeks so don't think I've deserted you if I don't reply to this post!

I'm not kidding about the gas flowing, you could do a good job yourself and think of the bragging down the pub!

I really would buy Des Hammills book, it was a huge help when I did my engine, view it as a tool to help just like a spanner!

Pete

[Sidecarbod]

Oh I forgot, I also made up some shims that are fitted under a couple of the valve springs, this was to get the on-seat pressure right.

I bet that you can buy them from somewhere!