3 replies to this topic

[Drobb1985]

I’m looking to learn about engines so have bought a pre A+ 1275 which was partially stripped and I’m now at the stage where I want to start the rebuild. I currently have a 1380 in my circuit racer so I’d like to build this new engine as a back-up to a similar spec using the spare components I already have (pistons/rods, lightened flywheel, race cam etc). First off is getting the block and head reworked where necessary. The problem I have however is what instructions I’d be giving to the machine shop. The bores will need to be increased and presumably offset for the 73.5mm pistons but how do I determine how much needs to be skimmed off of the block/head to gain a given CR? All of the literature I find on Google/YouTube has a “starting point” CR where they calculate the current volume and can then determine how much needs to machined to gain a desired CR. Is there any way of doing this when the engine is in bits?

[Spider]

To work out your final deck heights the best way is to do a dry build and measure it.

 

By 'dry' build, I mean normal in every way, only you don't fit rings and while not relevant here, you would fit gaskets, but without sealant.

 

You'd probably want to go much further with the dry build than just fitting the crank, rods and pistons, as you'll likely find other items needing machining and / or rectification.

[DeadSquare]

I know that tis is not the answer you want, but as this might become a full race engine, this sort of work needs to be done by someone who is not only a good machinist, but knows about race engines.

 

Much more money is wasted by people trying to save money, getting bits of the work done by different workshops, than the expense of having the complete job done by an expert.

[nicklouse]

I would never give a machine shop any instructions on how to do anything. I would only tell them what I would like them to do.

 

they should know how to do what they do.

so tell them what CR you want for the cam choice and they should be more than able to do the rest if you have supplied all the parts needed.

 

or read the yellow Bible and work it all out yourself and hope you got it right.