Hello fellow travelers. Here's one for you. I just rebuilt the B-20E in my '71 1800-E. Nothing fancy, just wanted to get it up to par. I did install a little stronger cam, but other than that, everything is standard. The pre-rebuild engine had never pulled good vacuum and I figured it was time. There was very little wear except for the cam which had a lobe or two worn badly and I figured that to be causing most of the problem. Well I got it running (using the oil pump priming technique I learned on this site THANKS) but it doesn't run well and the vacuum is low and fairly steady at idle, there's a bad hesitation in the acceleration until pushed to about 2000 RPM at which point the vacuum also rises into a normal range (steady). But what really concerns me is the compresssion test I just put on this engine. First test was done with warm engine and screw-in type gage. All cylinders showed 150 PSI + or - 1-2% Fine. So I check the green book and discover that 170-200 PSI is more like it. So I proceed to the wet test and all cylinders show between 185 and 205 PSI. I must assume that all this is related since what I know about auto mechanics says it should be. Where am I going wrong here? Ignition timing is correct. Valve timing and adjustment are correct. Can't find a vacuum leak to save me. Have I made some basic error in the assembly of this engine? What would explain the compression #'s ? Is it typical for a fresh engine to exhibit such disparity from dry to wet comp. test #'s until the rings are fully seated? I know there are some good mechanics out there with alot of Volvo knowledge. What do you think? THANKS Mike

The chances of your compression tester being similar to that quoted in the green manual are remote. So the actual values don't matter, just that they are even, which they are.
Any engine will show higher value with a wet test - the oil seals well at low cranking speeds, AND contributes to compression depending on how much you squirt in. Your values are still even.
The camshaft will reduce the values.
The head gasket thickness will change the values.
Drive it - hard. If there are no symptoms of an internal fault, all is well. What symptoms you do describe make it sound like it's running a bit lean.
I've ringed as many engines as I have put new pistons in. I do my own honing. None have ever burned oil, and they last for thousands of miles. Hastings and Grant make better rings than Mahle, if that's any consolation.

With the dry compression good I would think the valves are ok. The rings are probaly not fully seated yet as indicated by the wet compression. Regarding the lack of vacuum & the hesitation I would check the timing at full advance⎮-37 degrees at 3000 rpm] & the cam timing. If the dots line up on the cam & crank gears, then verify that the cam is not misground. I've heard of this happening on some aftermarket cams. By the way if you are using a newer formulation of oil be sure to find a zinc additive as they have removed most of the high pressure additives from the latest formulations. Oils used for diesel engines still have the zinc in them so use one labeled for diesel engines. Lack of zinc can cause rapid cam wear[especially flat tappet cams],even on a new cam. To check the cam timing you will need the "cam card", which tells you when the intake & exhaust open & close in degrees. Also, what is your vac. reading at idle? Good luck!

Mike M.

As George suggests, rings are the prime suspect if you have different wet/dry compression readings. I've never heard that this would be normal for a fresh rebuild. Of course they do say you need to take it easy on the motor for the first several hundred miles.

Did you just put in stock rings? Was there any machining done? I'm wondering if the rings are too small for some reason - either due to cylinder wear or machining.

I've read that poor vacuum is due to problems with the valves not seating fully or in the right sequence. Did you have a normal valve job performed?

Did you do the work yourself or pay someone to do this?

What cam did you install? Going to a larger cam from the D will lower the dynamic compression. You either increase the compression to match or you now have the opportunity to use low grade fuel.

I'd say your rings are OK given that the compression is the same in all cylinders, just don't baby it in the early stages of it's new life or your risk glazing up the bores.

You DID put in new rings, right? Might be they need to be seated in.
What end gap did you have on your rings?
--
George Downs, Bartlesville, Heart of the USA!

All rings, bearings, anything that wears out was replaced. Don't remember the end gap spec. Could it make enough difference to cause the symptoms I describe? When you say seated in, are you referring to the end gapping of the rings or something else?

Mike

Only if the end gap was very large. Should be about 0.016 to .022" for all B20s according to my green 1972 manual. Seating in refers to mating the surface of the ring to the cylinder.
Did the shop break the glaze on the cylinders or hone them?
--
George Downs, Bartlesville, Heart of the USA!

Hello,

You might just need to break in the rings by driving the car for couple of hundred miles, depending on what type of ring, cast iron or chromemoly.

I will not re-ring any motor until I have my machinist check the bores with a super accurate bore gauge.

The problem most people do not understand is that over time the bores will become oval due to the offset wrist pin in a stock piston and due to the direction of the thrust the piston receives when combustion takes place.

If the bore is oval, you can not expect a ROUND ring to seal on it and there is not such thing as a proper replacement ring to seal an oval bore that used to be round. The only solution is to overbore to the next size piston or resleeve the block.

Also, when I do a re-ring, it is critical to get the bores resurfaced to match the type of ring that is being used. Cast iron rings need a coarser surface than a chromemoly ring. Without the correct surface on the bores, a ring will never break in correctly.

BTW, in the last 20 years, I have only attempted 3 non-race engine re-rings. The first 2 were done very early in my Volvo career back in the early 80's. 1 was for a friend and that re-ring lasted less than 6 months before his 140 wagon was spewing so much smoke, you literaly could not see his car because of all the oil smoke coming from the tailpipe. The second was done to an engine that went into an early restoration on a 122 wagon which is still in the car and running, albiet for a fairly recent new owner and in serious need of a rebuild. The last was done about 5 years ago on an engine that was freshly rebuilt with new Mahle pistons. The engine was re-rung because the customer would not follow our advice to have the engine with dual sidedraft DCOE Webers, dialed in correctly using a rear wheel dyno. The carbs were running rich and the rings and cylinder walls were burned due to the oil being washed off the cylinder walls by too much fuel.
--
Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90501

Greetings, the cylinders were honed very lightly (the original cross checking was still evident on the cylinder walls). Local machine shop did the cyl. head - valve work, inspected the pistons etc. I assembled the engine. The cam is the Isky "street torque" marketed by IPD which should replace the stock cam (which was worn out for some reason) without causing valve train problems. I'm thinking that I goofed the ring install somehow or got the timing slightly off, or the dist. retard/advance is wrong. I can't see how the cylinders could be badly out of round if the original checking was visible on the walls. Thanks for all the input folks. I'll keep on 'til I get it right.
Mike