Just purchased 44mm BBK for Spree - Question

[gfisher99]

Hey guys,

I just purchased a 44mm BBK for an 86 Spree from Taz. I tested compression on my original cylinder yesterday and found 80psi cold, and 90psi with a little oil in the cylinder. I knew this was going to be an issue at some point, as the day I bought it, I took the cylinder off and noticed a pretty big, odd shaped scratch on the cylinder wall, along with cracks all the way around one of the side intake ports. Something has previously blown up inside, as there are a few nicks in the head itself.

My question is about the head modification. I have read a few posts that say the BBK requires you to take some material out of the head to give more clearance. What Dremel bit do you use to do this? How difficult is it?

Any help is appreciated..

Greg

[Trafficjamz]

Hey guys,

I just purchased a 44mm BBK for an 86 Spree from Taz. I tested compression on my original cylinder yesterday and found 80psi cold, and 90psi with a little oil in the cylinder. I knew this was going to be an issue at some point, as the day I bought it, I took the cylinder off and noticed a pretty big, odd shaped scratch on the cylinder wall, along with cracks all the way around one of the side intake ports. Something has previously blown up inside, as there are a few nicks in the head itself.

My question is about the head modification. I have read a few posts that say the BBK requires you to take some material out of the head to give more clearance. What Dremel bit do you use to do this? How difficult is it?

Any help is appreciated..

Greg

I used a solid carbide tile cutter bit in my dremel. I am also very very good at using it.
You might just wanna have a local machine shop do it. Or there are members on this forum who do it for cheap. (not me)

[Wheelman-111]

Greetings:

The complex calculation of ideal combustion chamber volume for a given bore/stroke and port timing exceeds simple-minded Wheelman Math "skills". Even people with those skills have to fine-tune through trial-and-error, and they usually have more than one engine to sacrifice to that purpose. To achieve surface uniformity and a perfect circle, the task should be performed on a machinist's lathe. Scooterwerx did a Magnificent job on my Malossi Machining and also cut a groove for an o-ring, eliminating the head gasket.

Toboggan online here has experience performing this Spree-cific job. I suggest you contact him. I would discourage you from attacking your head with a Dremel. Also the Scooter's.

[skeeter2]

I brought mine to a local machine shop. He cleaned up the minor head damage i had, and bored it to the size i needed, all for $20 bucks.

[gfisher99]

Cool, I would rather have it done by someone else too. What do you look for to find a local machine shop, and what do you tell them to "do"?

[Wheelman-111]

Greetings:

As a ballpark, the cylinder volume increases by 58cc/49.~cc, or around 15 percent. In order to keep the compression ratio about the same as stock, the cavity of the head's dome needs to increase in volume by that factor. Perhaps a bit less if you're planning for maximum performance with decent longevity.

The machinist probably knows a thing or two about engines and compression ratios, since he modifies cylinder heads for a living. So you can just explain your plans, ("I'm inceasing my bore diameter from 41mm to 44mm...") and ask for his advice. He should give you an explanation something like mine above. Depending on how much faith you put in his judgement, you must then decide whether or not to have the deed done. Most experienced machinists have numerous faded tattoos, and a filterless Camel super-glued to their lower lips.

Another option might be to stack head gaskets and measure static compression until you have a workable value. 1 or 3 added gaskets might be enough, but again, measure.