SC/912 Cylinder heights question

[Wm Webster]

In the factory B/C manual on page SE25 It mentions cylinders ...But does not address the SC Al finned cylinders. Page SE 52 gives the tolerences and wear limits of the SC engine but does not address the cylinder heights. The cylinder for the SC (i Assume) is the same as the 912. If you look on page E61 of the Factory 912 motor manual it states there are four cylinder height groups 5,6,7 and 8. My question is what height distance does each of these groups represent? You see I have three really good group 6 cylinders and two really good group 5 cylinders... What is the difference in these heights? Do any of you have a good group 6 cylinder you could sell me? I am trying to make a good usable set of cylinders for the motor I am about to build. Any help would be appreciated.

Wm. Bill Webster
#1534

[C J Murray]

Forget the book. Measure all of the cylinders that you are using and make sure that they are all the same from sealing surface to sealing surface. A variance of even .006" will result in a compression leak. This should be checked on all new cylinders since they are sometimes not right. A machinist can trim them to be equal.

[Wm Webster]

CJ... and your choice of machinist is?


Wm Bill Webster

[C J Murray]

Almost anybody can do it. Use a local guy.

[Mike Horton]

Bill, Cliff deftly skipped over the other determinates for cylinder, & piston reuse. Find the out of round limits, and have them checked with a dial bore ga., or other measuring device, to still be in limits. The other, more important clearance to measure, is the top ring, to ring land, the edge of the ring groove, in which the ring fits, and to determine if it is still in limits. If the top ring/land clearance is in limits, the others will likely be, as well. If either of these are not in limits, you will be disappointed in the results, and your resources might be better invested in new P/C, in my opinion, that is. If all are well in limits, you can use the two matched pairs, one pair under each side head, and if needed, machine the tall ones to match the short ones...

[C J Murray]

So, by the time you measure everything and trim the cylinders even you could have bought(almost) a brand new cheap set of pistons and cylinders(being careful to check that they didn't come with the grenade wrist pins). In the old days a rebuilder would search through his "good"(looking, not measured) used stash and find 4 that match and slap them in for a cheap rebuild that would last longer than the remaining life of the floors. Today people buy new.

[Martin Benade]

Cliff, that's an excellent description of how long a rebuild needed to last in the old days.

[C J Murray]

Martin, we made due with what we had and what we could afford, right? No sense throwing good money after bad when you already had the princely sum of $1400 invested in a rust bucket with "Speedster" written on the side. Today the car is too valuable to drive but is full of the highest quality expensive mechanical parts so it will drive perfectly! Joe Walsh wrote a song about things like this...." my Maserati does 185, lost my license, now I can't drive....life's been good to me so far"

[Jacques Lefriant]

Hi Wm
page 30 of the info please list the Birals from engine nos 820641/811362(earlier engines had Ferrals like S-90) heights 5-8 100.950-101.050 in .025 steps they also list the repair from 100.70-100.80. I can supply new forged pistons German made in 83.0 or 83.5mm stock compression if your cylinders will clean up. if you can not find a vendor who can bore them we can have that done also.
cheers
j
CJ if he has to use a 16 cam this is the way to go.

[Wm Webster]

Thank you all for your replies.... I have already checked the cylinders (measurement wise) I have three good ones ...with NO ridge at all where the rings stop on their outward journey...really great looking specimens... BUT the fourth cylinder has two long scratches that are .030 in. in depth.... a.little deep for me to use. All the pistons are in great shape... measured them also... I do have a really good group 5 cylinder (same condition as the 6's I have)... and yes I can send them to Ollies... and for $30.00 per cylinder they will machine them to all the same height and I will have a set to use. CJ... You see I try really hard not to use the cheaper brands of P/C's (overbores) because they tend to sink into the head. I prefer the original thickness of the cylinder wall... I think they give a longer service life.. And yes I can go buy a new set of Mahle's... but you gotta remember..... where I'm from even the doctors and lawyers are poor.lol Again thanks for your input... but I'm still really curious as to the actual factory measurements (height wise) for each designated group 5 thru 8. I've always wondered what it was..... And for what ever it's worth... that's forty years of my life.

Regards, Wm Bill Webster
#1534

[Ron LaDow]

Bill,
While the cylinders should be checked for consistent heights, it's also a good idea to place them on the case and check the fitted tops to make sure they are parallel and normal to a plane.
Over the years, some cases have 'mutated' to irregular forms and dimensions.