cylinder head design

[bis13]

there are two different designs of combustion chamber on the 650cc head. why? when was this changed? and which head is best to modify?
 also have a look at the class workmanship on this head, the valve guides have been driven in by a lunatic and i dont think this head has been worked on before so the factory have done this?!
 should i drive out these guides and refit some new ones or should i leave as it is i do believe it might be possible that the holes have not been bored out equally and to be honest this head was working just fine before i opened it up! your views would be nice thankyou.

[bis13]

more pics

[bis13]

and again..

[bis13]

valve guides ooer...

[Rusty's Uncle]

The head at the botton of the first picture looks like the later design and is probably the best one to go with, The top one looks like it might have had a skim but difficult to tell from the pictures. The valve guides are a bit of a mystery but it could be that the engine may have been run at some time under extreme heat / conditions and allowing them to shift. If they are still a good stiff press fit then they could just be drifted back into position. If they are slack then that would be a problem but do not bin it just yet. Are you planning to modify a head or just a clean up & polish  [-/

[bis13]

the valve guides are solid and will not budge so i can only assume i need to heat the head up to get movement the guides are knackered so they need to come out. as for the head i dont know what way to go as i am in two minds as to what i want reliability or more hamsters...i have new guides and valves already that are sitting around doing nothing so i might just give it all a bit of a polish up and bung them in as i have the second head so could go to town with that one and mate it up with the spare bottom half i have plus i have whats in the car so i can rotate them around and see what runs best...

[Pete126]

The second head has the same combustion chamber shape as the Bis with the large squish area, Could be a higher compression head

 

[Rusty's Uncle]

No you do not heat the head when removing or fitting valve guides. You just need a suitable drift / punch & a hammer  [-/

[GTMaster]

Yes, it looks like the bottom head (in the first picture) is of the later series 650 engines (650E, A1076E) as that has a higher compression ratio ( 1: 8 ), the one above it might be off an earlier 650 (A1) or 600 (A000) comp. ratio 1:7.5, don't know as i haven't seen heads off earlier engines... the valve guides were probably changed at some stage and weren't pushed properly into place.

[DEYAN IYI]

The best way to fit the guides is to cool them in liquid nitrogen and then leave them in the wanted position.

The Panda 30's head 8:1 has also the new type of chamber:

[smallcox]

Hi Bis 13,

I agree with all above,  Ifound early engine had the head in your top picture, and later 650 head has the head with more shrouding and squish area.

Moding the later head is the one to go for as the sqish area is important for quicker/fuller burn when ignited. I have modified both and found build quality about the same, but the head without the squish area is prone to pre ignition when moded( this may be due to slower burn rate?) as for removing the guides you may require a formed tool that applies to the press and push them out from the port side.

The later head be aware that as valve lift increases so does valve shrouding due to the angle off travel that the valve moves through, but unless you increase valve size this I believe would almost be un-notible.

Ps I used both heads to the same spec on my turbo and beleive the later is better

[bis13]

the liquid nitrogen technique is the opposite of the heating so theres another way to go about it but i prefer to keep my fingers albeit burnt from heating the head up.... i have seen the heated method a few times and makes it easier to remove and insert guides. i have now either got to fabricate a guide tool or buy one so thats my next mission the last option is getting someone else to do them but to be honest i want to play with it its my toy! thanks for the feedback on the two head designs i had kind of already deemed the second head the better of the two to modify (by flipping a coin .. joke) .