Merlin Heads

mgbloke · Post by **mgbloke** » Sun Jun 13, 2010 8:47 am

My first trackday with the latest Mods went very well but I have a few issues to sort out.
Car felt really good and I noticed the extra power accelerating from 80mph I could leave black tyre marks.
In a couple of corners the car feels better in 3rd gear and when accelerating out rpm reaches just over 6k when it makes a loudish mettalic noise and the power drops off until I back off. I can only assume that this is valve bounce. can anyone help me out here as I have not experienced it before.
The merlin heads have single valve springs and was told by RS that they would be OK for the Mechanical 238 cam. Now wondering if these springs are man enough.
Also Im back to the old problem of the oil catch tank slowly filling up with oil although I have edelbrock baffled breathers on each rocker cover. This only seems to happen when using very high revs and is a symptom of using the yella terra roller rockers. Im using the 1.5mm oil restrictors from my other heads but the rocker covers dont have internal baffles like the rover ones.
All in all I am very happy with the performance especially as a few spectators mentioned how much faster the car looked than last year.

Cheers

Mark

CastleMGBV8 · Post by **CastleMGBV8** » Sun Jun 13, 2010 8:59 am

Mark,

Those single spring are not recommended for track use and Real Steel say that in their parts list, the quality of the information does depend on who you speak to at RS.

Tony (V8kid) had issues with these springs going soft and had to change to doubles I think.

Kevin.

mgbloke · Post by **mgbloke** » Tue Jun 15, 2010 3:55 pm

The information that I have is that they are Chevrolet valve springs.
Waiting for RS to get back to me with more information re upgrading them.
For now I will limit the rpm.

Considering the flow figures available for the heads are dissapointing I am amazed at the amount of extra power & torque Ive got.
I Wonder if others are getting similar results.

Cheers

Mark
MGB GT V8 4.6
277rwbhp 970kg

CastleMGBV8 · Post by **CastleMGBV8** » Tue Jun 15, 2010 4:20 pm

Mark,

Did you check the installed height of the valve springs?

An alternative single spring is the Beehive type which because of the taper towards the top doesn't suffer the harmonics problem of a single straight spring, you do need smaller retainers which are also lighter.

Loads of info here.

http://www.google.co.uk/#hl=en&source=h ... 7a7970bfae

Re the heads, just shows that flow figures are not all the story.

Kevin

mgbloke · Post by **mgbloke** » Tue Jun 15, 2010 5:07 pm

Kevin
No I didnt check the installed heights of the springs.
I have actually been looking at the Bhive springs but need more info from RS.

Now im thinking if I had the heads professionally ported next winter, and maybe a 248 cam, what would the gains be? On the other hand maybe its fast enough!

Mark

CastleMGBV8 · Post by **CastleMGBV8** » Tue Jun 15, 2010 6:33 pm

Mark,

"On the other hand maybe its fast enough!"

Souds like it and unless you intend to actually compete then a few more BHP is probably not that important.

Personally I would consentrate on reliability, valve bounce is not a good idea and if you regularly experience it then the valves and valve gear will suffer, in extreme cases you can drop a valve with very expensive consequences.

Looking at the RS literature they recommend the DW550 double springs for the 238 or 248 cam so either those, or a set of Beehives with the correct spring rating would do the job, but it is important to set the installed height correctly otherwise they will not work efficiently.

It isn't just the peak RPM that effects the valve springs but sustained high RPM usage that is experienced on track which causes the springs to overheat and lose tension.

I f you look at some of the slowmo videos it is quite frightening to see how much the springs occillate as harmonics build up.

Kevin

SuperV8 · Post by **SuperV8** » Tue Jun 15, 2010 11:23 pm

Wow, very interesting.

http://www.youtube.com/watch?v=_REQ1PUM0rY&NR=1

So much yet to learn

Tom.

CastleMGBV8 · Post by **CastleMGBV8** » Tue Jun 15, 2010 11:42 pm

Tom,

That's a fairly extreme example and you can see that the valve spring has virtually no seat pressure and the very large clearance between the valve tip and the roller rocker is probably not helping either.

However it does indicate what can happen if the valves and springs are not installed correctly.

Kevin.

mgbloke · Post by **mgbloke** » Wed Jun 16, 2010 7:15 am

I did take all the valves out when cleaning up the ports/runners and put them back in exactly the same place with the same shimms so hopefully the heights are OK
Its been a lot of work since November as apart from the heads I had the exhaust issue and fitted Mk1 golf wheelarches to the mg front wings. also had to make some bushes for the steering column. On top of all this I also upgraged the brakes modifying the pedal box and changing master cylinders & all new brake pipes . The whole front suspension was re vamped & powder coated.
Basically Ive had enough of working on the car for now. Going to get a rev limiter and set the limit to avoid the valve bounce/float issue.
Really like the look of the Beehive springs and now I have got some time to sort this out.
This weekend I will make some additional baffles for the rocker covers and hope that solves the oil/breathing issue.

Next track day is 25th at Castle Combe again, its a Porsche day so should be very interesting.

Cheers

Mark

minorv8 · Post by **minorv8** » Wed Jun 16, 2010 9:13 am

I have tried to find beehive springs to replace the springs in Merlin heads. Have not had success since either the spring dimensions are not suitable or the spring rate is way too stiff.

mgbloke · Post by **mgbloke** » Wed Jun 16, 2010 12:50 pm

Jukka
Thats very interesting. What have you found out about the Merlin springs are they in fact Chevrolet items. Would be nice to know which engine they are from.

Cheers

Mark

minorv8 · Post by **minorv8** » Wed Jun 16, 2010 1:08 pm

Wild guess is some basic Small block Chevy springs, could be from a mild 327 cu.in.

The closest beehive one I have found is Compcams 26113, with 1,061" bottom OD, seat load 93@1,570", open load 198@1,020", coil bind 0,952"

These are for Ford modular 2 and 3 valve engines.

There is also a 26123 version for 4 valve modular engines but it is higher rate and limited to ,500 valve lift.

JP. · Post by **JP.** » Wed Jun 16, 2010 4:52 pm

CastleMGBV8 wrote:Mark,

Those single spring are not recommended for track use and Real Steel say that in their parts list.

Real Steel does not say this in the partslists for the heads.
Heads come assembled with valve springs.
Instalation instructions does not say which springs are used.
So till RS is responding nobody is shure which springs are used on de Merlin heads.

Have no problems myself with these heads till 7000rpm (Viper Hurricane cam & Rhoads lifters & stock rockers on a blown engine).

kiwicar · Post by **kiwicar** » Wed Jun 16, 2010 5:28 pm

Hi
If you know the spring diameter, closed pressure, installed height and open pressure at max lift (ie rate) cant you just order the right ones from someone like Isky? from the chart that is here http://www.iskycams.com/ you don't need to know which car they came from!
That is how I ordered mine.
Best regards
Mike

mgbloke · Post by **mgbloke** » Wed Jun 16, 2010 7:12 pm

Mike
Thats just my problem, I dont know the diameter and spring rates without taking it all apart which i dont want to do at the moment. Waiting for information from RS but as usual they are taking their time. Will have to chase them up.

Mark