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PV, 120 (Amazon), 1800 General Forum for the Volvo PV, 120 and 1800 cars |
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Cylinder HeadViews : 750 Replies : 4Users Viewing This Thread : |
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Oct 19th, 2020, 22:37 | #1 |
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Cylinder Head
I have only recently joined the Owner Club so have not seen past questions and issues, so my question may have been answered some time, even some years ago, and I would be glad if someone could direct me to past comments if appropriate.
I have a 1963 Volvo 121, which I bought in 1973 and have therefore owned it for 47 years. I did a lot of work on it in past years (mostly in the 80's) and after a complete engine re-build in 1978, I changed the cylinder head some time in the eighties to a B20 head. It has a Weber 36DCD carburettor without vacuum connected. I have put up with a lumpy tickover for years, blaming the carb for constantly getting dirt into it and I have dismantled, cleaned and re-assembled the carb countless times. I have recently been made aware that a B20 head and B18 engine do not really go together and I should have had some machining done to adjust the head. So can anyone advise me what I should do to the head to improve the engine. I am planning to remove it with a view to having work done on the valve seats for unleaded fuel. Thank you for your help |
Oct 19th, 2020, 23:06 | #2 |
Trader Volvo in my veins
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The compression ratio will be very low due to teh bigger chamber volume of the B20 head.
What I would be doing is boring the B18 to B20 piston size, you could even consider going with a longer stroke if you wanted It is either that or go back to a B18 head |
Oct 20th, 2020, 13:51 | #3 |
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Last Online: Feb 11th, 2022 04:15
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(In addition to the cylinder head information)
If you are constantly getting muck into a carb you need to tackle the problem head on. Think new fuel tank / sealing fuel tank - fuel filters - cleaning out the entire system. Consider also the fuel you are using. For example:- For ages now Euro 95 has essentially been E-5 (5% ethonol) which can cause trouble for vehicles (like classic cars and motorbikes) that don't get used frequently. There are additives out there that will help stop the water content in modern fuels from seperating...
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Oct 21st, 2020, 01:51 | #4 |
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Living in the colonies (and having no experience with Volvo B18 or B20 engines), the diagnostic description of "lumpy tickover" has little meaning for me.
But I have difficulty imagining that use of a B20 head itself would result in a "lumpy tickover". The car may have a lower compression ratio because of an oversized combustion chamber, but it would just be down on power. You describe that the engine was rebuilt, so my question is: what are the characteristics of the camshaft that was utilized. A performance camshaft may result in a loping idle and poor performance in the lower portion of the power band. As you pull away from a standing start, the car may buck and hesitate until you get into the camshaft's power range. Another option is that mice have made a nest in your exhaust system, with the result that you have too much back pressure. That too might cause something that feels like an internal backfire back into the engine. Not exactly the same an a misfire. Perhaps a restrictive exhaust manifold would result in the same or similar symptoms. The third option is that you may have sticking valves. If the valves are sticking because of inadequate clearances, it might feel like fuel starvation or a misfire at higher RPMs (when the engine is hot). Often confused for both ignition and carburetor misfire. Do let us know what you do and how it addresses your issues. Last edited by blueosprey90; Oct 21st, 2020 at 04:01. |
Oct 21st, 2020, 04:56 | #5 |
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I was unable to edit the above post so add the following here.
The issue of sticking valves: This would be a suspect if you installed a rebuilt head with new valves and new valve guides and if the machine shop neglected to provide the correct clearances. With regard to the changes to the head that you are considering, you might peruse this manual as it may provide some clues. Start off by measuring the volume of your combustion chambers so that you can calculate your compression ratio. Cheers! http://volvo1800pictures.com/sweden/...6_5emqDbNoR6z0 Last edited by blueosprey90; Oct 21st, 2020 at 05:00. |
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