Hurley engine out. My engine in...Help??

[Jonathan_F]

Hi I\'ve been busily rebuilding my Hurley engine. I shall be posting a full report when I\'m done explaining the problems and errors that caused the premature failure of this engine (3k miles for a £3.3k engine).

I\'m at the point where I have a collection of shiny clean ported engine components and a large hole in my engine bay. I want to ensure I have included all the little tweaks I can.

I haven\'t balanced the rotor/crank assembly. It would be nice to be able to raise the rev limit to 8.5k (car pulled stringly to 8k prior to failure) and I believe that by improving the balance that this can be achieved. I was going to balance the rotors as a pair but i\'ve realised that as its a 90° crank this will not make a scrap of difference. My question is: has anyone come up with a static balance method i can do at home that will improve the balance of my engine?
I have read in the mazda competition manual the nominal bob weight balance mass (used for balancing operation in place of rotor assembly) and the nominal rotor mass required for balancing. Can I correct the bob weight mass for the difference from nominal of my rotor mass\'s and statically balance.
I have nothing but some V-blocks and an electric drill. I was going to mass load the rotors to achieve the calculated balance bob weight mass and then spin the assembly and remove mass from the lowest point until I achieve a balance.
Has anyone tried this and can it improve matters? I am using different rotors to the originals and I\'m worried there may be a balance issue.

I wanted to increase the oil pressure also. To do this I was going to shim the oil pressure release valve spring. Has anybody done this and how much should I shim it by?

Thanks for any help given,

Jonathan

[Brett]

What model of engine is this?  And which rotors have you swapped to?

:wave

[MikeLMR]

Have you swapped the front counterweight and the flywheel and or rear counterweight to match the new rotors ? or are they the same type of rotors but "new" to this engine ?

[Jonathan_F]

Right. Sorry. Its a 13B twin turbo. I am using the rotors from another engine that had oil supply failure so can\'t use the crank. I do have the flywheel and pulley and can use these.
I have read that rotors cancel each other out but i\'m not sure about my 90° crank angle now (from memory this morning). If it is 180° then the counterweighs are there purely to remove the dynamic couple. I can then do a static balance with reasonable confidence. It is a shame I cannot afford to have a full balance. Many thanks. Jonathan

[Brett]

IIRC they are 180 on 2 rotor.

[Jonathan_F]

IIRC they are 180 on 2 rotor.

Right then. So if I balance the rotors as a pair then that WILL improve the balance of the engine and is a worthwhile exercise.
Looks like I shall be building a simple pair of balance scales.

Now. About the oil pressure...

[Archbish]

but surely it is the difference in moment around the centres of gravity???

[igy]

No need for any type of balancing if you ae using FD rotors with FD counterbalances and the rotors have the same letter marking.  You could spin that motor to 10k on a regular basis with the right porting and turbo, and it would last a long time.  With a couple of oil mods and some clearancing, you could do 11-12k easy.  If you are not getting paid to race, don\'t waste your money/time for the extra 500rpms of rev you are looking for.

[Jonathan_F]

Thanks for your input igy, I think that I should be deciding how much balance I require in my engine. No disrespect intended but I like to reduce all forces and losses in an engine as a matter of course. Its good practice and will help with longevity.

Archbish, as I understand it the rotors balance each other but because of their offset along the axis of the crank there is a secondary couple that is balanced by the couterbalances. By balancing the rotor pair I can remove the primary imbalance. The couterbalance/crank/pulley assy should be in balance also.
When I have completed this exercise I shall post my results.

For the oil pressure increase. Has anybody done a modification in this area?I am struggling to get the roll pin out of the release valve. Its welded in so i\'m drilling it out. I won\'t be able to measure the blow off pressure until the engine is asssembled so i\'d like to know the shim size commonly used. If at all.
Many thanks.
Jon

[banned advertiser]

Igy is right about the lettering on the rotors, make sure they are the same, they are balanced and marked by Mazda for that reason.

[antnicuk]

As igy says, make sure the rotors have the same letters or are only one out and thats all you really need to do,  each rotor is filled with oil any way which affects the weight while in rotation so you wont be able to mimick it on a test bed very easily.  

As for more revs,  with a little bit of clearance on the rotors the engine will physically be able to rev more but if you have stock twins, you wont neccessarily have more power at the higher revs as you will find that depending on porting, your power probably drops off at about 8k or even less anyway, so there is no benefit reving higher.

Mine was on the rollers yesterday and the power starts to die off a little at 7500 rpm but on the road it feels like it just keeps on pulling but it isnt actually the case.

 If you have a high flowing turbo (T51 etc) and the inlet porting is right then you can raise the power band.

[mullins]

Looks like I shall be building a simple pair of balance scales.

It more like balancing a tyre isn\'t it? Scales will only measure the weight!

Is it just be or are Hurley engines cr@p?!

[deanflowers]

My brand new hurley engine struggle to get to 13,000 before i\'d had enough and went to rebuild it,

strange that the brand new engine had second hand housings i think

[sadgoth]

My brand new hurley engine struggle to get to 13,000 before i\'d had enough and went to rebuild it,

strange that the brand new engine had second hand housings i think

I\'d raise that as an issue if I were you, if an engine is sold as new it should have new housings, unless it is specified that the housings are 2nd hand. (I had good second hand housings in my engine, but I requested that from RX motors)

[stuart wizy]

when you say race clearenced rotors do you mean the clearence of rotor housing width dimesion minus rotor width dimension?
Or do you mean on the sides of the rotor at the corners?
Ive cleareced my rotors .015" deep across the sides where the bore is for the corner seals not breaking in to the side seal groove so it doesent burr it up.
A tuner told me to do this for high revs as the shaft can distort slightly and make your corners rub your side housings.
Also ive found on 2 diferent 13bs that ive stripped,the corner seal bore is a big weak spot and the apex seal groove is always wider here than in the middle of the groove due to the corner seal  bore.
on 2 rotors ive seen, these weakened corners have flared outwards due to pressure on the side of the apex seal by .008" .
this is enough to rub your side housings almost.
as for balancing, ive got a crank built up with rotors and weights on, in correct possitions and i put it between centres and it does move slightly on its own weight, but like antnik said this will change when rotors are full of oil.