Advice about rebuilding a 3.9 engine

[Vulture]

Hm, I see. Is the following info on specs detailed enough?

- Measured and polished crankshaft, "equalised" con rods and pistons, crank pulley and (lightened) flywheel also balanced
- Honed cylinders
- New piston rings, standard pistons
- RPi Engineering Stage 3 Heads
- Piper 285 camshaft
- Weber/Edelbrock 500 carb
- Standard lifters, preload set according to manual

If I forgot anything, enquire. My brother nailed it all together; it's not the first time he does that, only the first non-standard RV8. The engine block and heads are going to my machine shop tomorrow for disassembly and inspection. With a bit of luck I will know further details on Thursday.

One thing I'm sure about, though, is that I want to replace all the valve springs. If one can break, so can the others. Can anyone give me recommendations for "uprated" springs suitable for my setup? I thought the ones RPi are using are already uprated, but it seems like I was wrong. OR, of course, there is a reason why the spring broke, e.g. a piston ramming a valve. Which shouldn't happen at 2000 rpm, should it?

[john 215]

Hi Vulture,
Sorry to see your horror pics,i would guess that the valve spring broke,valve dropped and took a hit from the up commimg piston ouch!!Is there any marks on that piston?
Bit concerned as going to be running the same heads Will be running Real Steel springs part no DW550.
Look forward to more pics and news hopefully not all bad.
Cheers John.

[Boosted LS1]

Hi Vulture,
i would guess that the valve spring broke,valve dropped and took a hit from the up commimg piston ouch!!Is there any marks on that piston?Cheers John.

That's a likely scenario as it would be unusual for an inlet valve to kiss a piston under normal circumstances.

If the valve's bent then it must have hit the piston. Easy to check for a bent valve.

Oh, are the valve springs coil bound?

Boosted.

[sidecar]

OR, of course, there is a reason why the spring broke, e.g. a piston ramming a valve. Which shouldn't happen at 2000 rpm, should it?

If the cam timing was wrong the piston could hit the valve even when you turn the engine over by hand so it could at 2000 rpm. The only reason that higher revs make it more likely to happen is that the valve can float if the springs are not of the correct rating. Also conrod stretch and bearing clearances can play a part in this. (if the cam is still fitted you can still check this).

Having said all that if the timing was wrong I'd expect other valves and pistons to show at least some evidence of contact.

I agree with "Boosted" it could well be that the spring went coil-bound.

You should talk to RPI before you get your machine shop to dismantle the heads, They may want them back and if the problem was at their end they should give you a new set.

I hope you get it sorted.

Regards,

Pete

[Vulture]

Hi @ all.

One thing I forgot to mention earlier I think is, thank you so much for all the advice you're giving.

I contacted RPi via email, and I got an answer soon after my last post here. It says that they can't tell why the spring broke without seeing the engine, but they will repair the heads and provide me with all I need to re-install them... free of charge! Chris also says that it's most likely not a fault of the spring because thousands are made from the same batch of wire.

If this is true (almost sounds too good to me), I still have to work out why it broke in the first place. The pistons don't have marks from any valves hitting them as far as I can remember (I'm over 150 miles away from the engine atm).

@John: I would only start being concerned about the heads when they start causing you problems.

Again I have to ask: What does "coil bound" mean?

[sidecar]

Hi @ all.

One thing I forgot to mention earlier I think is, thank you so much for all the advice you're giving.

I contacted RPi via email, and I got an answer soon after my last post here. It says that they can't tell why the spring broke without seeing the engine, but they will repair the heads and provide me with all I need to re-install them... free of charge! Chris also says that it's most likely not a fault of the spring because thousands are made from the same batch of wire.

If this is true (almost sounds too good to me), I still have to work out why it broke in the first place. The pistons don't have marks from any valves hitting them as far as I can remember (I'm over 150 miles away from the engine atm).

@John: I would only start being concerned about the heads when they start causing you problems.

Again I have to ask: What does "coil bound" mean?

Good news from RPI!

Coil bound is when the spring is compressed so far that all the coils of the spring touch each other, the spring can not be compressed any futher.

If the lift of the cam still has some way to go then something has to break, either the spring, the push rod, or the rocker. As you have a higher lift cam than standard not only do your springs have to be stiffer to avoid valve float, they have usually have less turns wound onto them than standard so that there is more space between each coil. The other method is to machine the head where the valve sits but this reduces the pre-load on the spring so it all has to be worked out before hand. Each spring manufacturer will give a minimum clearance between each coil at full lift.

With stage 3 heads they have probably taken this into account but its worth telling RPI what cam you are running.

Regards,

Pete

[Vulture]

Well I bought all my stuff at their place, all in one go, and told them what I wanted when I ordered via phone. I believe them to be professional enough to know that I will probably install all those items in the same engine. Valve lift, cam timing and, again, preload are in my Top 5 of not having caused the problem.

One thought I had this morning: can heat cause a spring to break? I used to have heat issues on another engine with the same carb and manifold. When I reinstalled the standard twin carb installation, temperature stayed at normal level. Now the 3.9 didn't exactly overheat, but the temperature usually was at a bit higher level than my old 3.5. Can this have caused just about the right amount of additional stress to cause a spring break?

[sidecar]

Well I bought all my stuff at their place, all in one go, and told them what I wanted when I ordered via phone. I believe them to be professional enough to know that I will probably install all those items in the same engine. Valve lift, cam timing and, again, preload are in my Top 5 of not having caused the problem.

One thought I had this morning: can heat cause a spring to break? I used to have heat issues on another engine with the same carb and manifold. When I reinstalled the standard twin carb installation, temperature stayed at normal level. Now the 3.9 didn't exactly overheat, but the temperature usually was at a bit higher level than my old 3.5. Can this have caused just about the right amount of additional stress to cause a spring break?

I doubt that you could get enough heat into a spring to actually change the temper of the steel and thus cause it to break. The motor would burn off the oil or seize up long before then.

Regards,

Pete

[ihatesissycars]

It could just have been a defective spring, even though its new it doesn't mean its going to be completely fine as if everything new never went wrong you'd never need a warranty.

What have Rpi said?

[Vulture]

It could just have been a defective spring, even though its new it doesn't mean its going to be completely fine as if everything new never went wrong you'd never need a warranty.

What have Rpi said?

I am aware of that, but according to RPi, the possibility of a faulty spring is diminutive.

There are many reasons that can cause spring failure, but without sight
of the installation I cannot guess with complete assurance

I can though offer to repair your head and provide gaskets bolts etc
free of charge

I may be simple just to say we supplied it so it must be our fault, but
we supply so many hundreds of heads without fault over 22 years
No matter how slight there is always other possibilities and I will
mention if only for the sake of mentioning them

Installation preload
Rocker and shaft condition
Camshaft end float
Lubrication to valve guides
Over revving especially on downshift and mostly unintentional
Engine head temperatures
Contanimates or small debris in the engine

I agree that it should not happen but it did, its very unlikely to be a
fault of the spring as they are wound from massive lengths of wire in
batches of many thousands
I will though be happy to take the sting out of the problem if you would
like

Kindest regards
Chris

That is the email I got from them. The only possibilities Chris stated that I can't rule out are the temperatures and the contaminates or small debris in the engine, though both seem unlikely. Ah well, I'll probably send the heads back to them for inspection, it's what they do after all!

The block has gone to the machine shop today, but they don't have time to inspect it yet as one of their engine specialists is sick. I'll hopefully get an answer from them concerning the state of the block, crank etc. in the next two weeks. All I can do until then is wait. *sigh* But at least the car is on the street again with an old 3.5 SD1 carb engine my brother had lying around.

[Boosted LS1]

I think that's a good reply from Chris at RPI.

Boosted.

[HairbearTE]

I must say its nice to see good customer service. RPI sometimes take some stick for their prices but their attitude and customer service is great in my experience. I once had to pick up a spare bonnet for the datsun and the guy I was getting it from was in norwich. On the way back I had some time so I thought i'd pop in to RPI and have a look around. Never been before, didn't know them, didn't call to say I was coming. When I got there I said hello and that I was just in the area from london and could I look around. I was introduced to Holly who builds the engines there and he showed me a few engines he was working on at the time and some customer vehicles. He showed me the laminated spec sheets that they produce for every engine they sell and keep for reference. I must have been there an hour chatting and never was I made to feel like I was a hinderance! I didn't spend a penny with them that day but I was made to feel welcome nonetheless.

[Vulture]

Hello, it's me again. I just got news from my machine shop. They told me that 6 of the valve springs of RPi's Stage 3 heads were about 5 mm shorter than the rest. This does not sound very good to me and it does shake my trust in RPi Engineering quite a bit. If they used different types of springs on my head, maybe they build all their engines with a certain amount of neglect? Or are different length valve springs normal on an RV8?

[sidecar]

Hello, it's me again. I just got news from my machine shop. They told me that 6 of the valve springs of RPi's Stage 3 heads were about 5 mm shorter than the rest. This does not sound very good to me and it does shake my trust in RPi Engineering quite a bit. If they used different types of springs on my head, maybe they build all their engines with a certain amount of neglect? Or are different length valve springs normal on an RV8?

That sounds bad!

What does RPI have to say about the springs?

[Vulture]

Hello, it's me again. I just got news from my machine shop. They told me that 6 of the valve springs of RPi's Stage 3 heads were about 5 mm shorter than the rest. This does not sound very good to me and it does shake my trust in RPi Engineering quite a bit. If they used different types of springs on my head, maybe they build all their engines with a certain amount of neglect? Or are different length valve springs normal on an RV8?

That sounds bad!

What does RPI have to say about the springs?

Nothing yet. I wrote them an email this morning, but I'm still waiting for a reply.