37 Cadillac engine rings

[Eric 21241]

Greetings,
I had a slight miss in my engine, one cylinder was out of wack. I put compressed air in the cylinder to find the compression loss which turned out to be the crankcase pointing to rings.
I discovered the bore was 40 at the top and 30 at the bottom of the cylinder, the piston was only 20 over and the rings gap (supposed to be .oo7} was 1/8".
I want to rebuild the engine but not now, later in the winter perhaps.
My question is Can I get away with a 30 over piston and rings.
will it work as a temporary fix? Anyone ever done anything like this before with success?
Best regards to all

[Dug Houston]

Boy, that sounds like engine wear with a capital"W"!. I would guess that in order to clean up your cylinder bores, your machinist will recommend an .060" rebore. It might be possible to rebore out to the .040" and get away with it, but in order to be sure that the cylinders are clean, a 60 thou rebore will be the best.

When I got my 41 convertible sedan a few years ago, the block had rust in the bores, and we were able to clean it up with a .060 rebore. It does raise the displacement appreciably, and I have to say that its the spunkiest 41 engine Ive ever driven! Youll notice the difference.

[Bruce Reynolds # 18992]

Gday Eric,

I second Dug, but Doug is his real name, on the .060" overbore.

Even though your bore might "clean up" to .030", it might actually be worn a fraction off-centre so that when bored to .030", at 90 degrees to the crankshaft, you still might have sone wear marks on one side of the bore.

When selecting the size of pistons to get, the Machinist will be the best person to listen to, as he will be the one doing the job, and will want you to be a very satisfied customer.

Dont forget to get the whole recipricating mess balanced before assembly.   You will be truly surprised at the difference a good balance job does to engine smoothness and power.

Bruce,
The Tassie Devil(le),
60 CDV

[John Tozer # 7946]

Dug, Doug and Bruce,

I have  flathead military engine that has some rust damage to the bore of one cylinder ("Someone took the plug out in the rain...."). I have been told by a reputable engine rebuilding Co. that they can over-bore the cylinder in these flatheads, fit a sleeve and bore it to 20 thou over to match the other cylinders. Do you have any experience of this "fix" and do you have any thoughts on it?

Regards,


John Tozer

[Bruce Reynolds # 18992]

Gday John,

Installing sleeves in Cylinders is not a problem at all, as long as it is done correctly.

I once had a 427 Chev and all the cylinders were overbored and sleeved out to allow .060" oversize pistons, and never had a problem with it, even redlining the emgine to 7,500 rpm.

If one cylinder is a problem, then there is no reason why that single cylinder cant be reconditioned.

Bruce,
The Tassie Devil(le),
60 CDV

[Harry Scott]

I had to put sleeves in two of the cylinders of my 41. The sleeves the machinist used were for a Ford 300ci 6 cylinder. The block was then bored .040. While the rebuild is still fairly new there have been no problems so far. I would not try to average the taper and use a piston in between. The taper may not be consistant and then you would have a more serious problem. Good Luck.