MGB & GT Forum
Early 18G engine block questions?
Posted by riley1489
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Mar 1, 2015 09:41 AM
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I am in process of building a 18G 3 main engine. I notice three curiosities that perhaps someone can enlighten me.
#1; there is a boss on the oil filter side of the block. This is tapped & plugged, (slot head plug in 2nd photo). The tapped thread matches that of the oil dipstick tube. My guess is another vehicle used this style block and the dipstick was installed in this position? If so I assume the MG place dipstick would be plugged? Confirmation?
Lower boss, front of engine to right side of oil dipstick boss;
#2; there is a machined boss just below the oil pressure relief valve. This is a blanked hole, is 5/16" fine thread tap and a bolt is in it. The bolt has no apparent use. Again another engine/car application?
Lower hex head in photo;
#3;
Markings on the block deck adjacent to the cylinder bores. In this case a diamond shape with 2 enclosed.
Ideas?
Thanks,
Bruce
Life's most persistent and urgent question is, "What are you doing for others?"
#1; there is a boss on the oil filter side of the block. This is tapped & plugged, (slot head plug in 2nd photo). The tapped thread matches that of the oil dipstick tube. My guess is another vehicle used this style block and the dipstick was installed in this position? If so I assume the MG place dipstick would be plugged? Confirmation?
Lower boss, front of engine to right side of oil dipstick boss;
#2; there is a machined boss just below the oil pressure relief valve. This is a blanked hole, is 5/16" fine thread tap and a bolt is in it. The bolt has no apparent use. Again another engine/car application?
Lower hex head in photo;
#3;
Markings on the block deck adjacent to the cylinder bores. In this case a diamond shape with 2 enclosed.
Ideas?
Thanks,
Bruce
Life's most persistent and urgent question is, "What are you doing for others?"
Mar 1, 2015 11:21 AM
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Bruce:
I can answer your first question. Yes, it is for the dipstick on different models. The ZA/ZB Magnette used the same block. On the Magnette the deep part of the oil sump is forward to clear the suspension crossmember. The dipstick location is moved forward to match, right below the generator.
Lann
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I can answer your first question. Yes, it is for the dipstick on different models. The ZA/ZB Magnette used the same block. On the Magnette the deep part of the oil sump is forward to clear the suspension crossmember. The dipstick location is moved forward to match, right below the generator.
Lann
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Dave Headley
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Mar 1, 2015 11:30 AM
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balloonfoot
Lloyd Faust
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Mar 1, 2015 11:56 AM
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#2 is not the attachment point for road draft tube. It is the attachment point for the rear carb overflow pipe.
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Law of Logical Argument - Anything is possible if you don't know what you are talking about.
"Anyone with an intense emotional interest in a subject loses the ability to observe it objectively: You selectively perceive events. You ignore data and facts that disagree with your main philosophy. Even your memory works to fool you, as you selectively retain what you believe in, and subtly mask any memories that might conflict."
Mar 1, 2015 11:58 AM
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Well actually, no other car ever used the 3 main MGB block, but it would be correct to say that the block from which is was developed (the generic 1622 block) was used in various cars and the different holes needed for them were left in the patterns when the engine block was expanded to 1798. Probably just easier and cheaper not to bother eliminating them.
Bill
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Bill
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Current: 1958 MGA Twincam (race car (170 bhp)),1962 MGA Deluxe Coupe (98 bhp)
1957 Jamaican MGA (200 bhp)1965 1971 Jensen Interceptor (350 bhp)
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Recent: 1969 MGC roadster (175 bhp),Jensen CV8 (375 bhp),
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dipstick
Kenny Snyder (RIP)
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Mar 1, 2015 12:11 PM
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Picture #1 & #2, that engine was supplied for many applications including stationary fire and irrigation pumps with front sump oil pans, thus the forward dipstick.
Picture #3. "Bore size code or sleeved bore designation for the corresponding cylinder.Many of the early 3-mains had factory sleeves."
I have seen (and have one) several original MG Magnette blocks that are factory sleeved.
Be safe out there.
Kenny
Picture #3. "Bore size code or sleeved bore designation for the corresponding cylinder.Many of the early 3-mains had factory sleeves."
I have seen (and have one) several original MG Magnette blocks that are factory sleeved.
Be safe out there.
Kenny
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Dave Headley
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Mar 1, 2015 12:31 PM
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Topic Creator (OP)
Mar 1, 2015 01:10 PM
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In reply to # 2930363 by fast-MG.com
#3. bore size code or sleaved bore designation for the corresponding cylinder. Many of the early 3-mains had factory sleaves. Why? I don't know.
I neglected to mention that the corresponding pistons are also carrying the 'size code' stamping.
If I understand well, this bore size code was established at the machining of the block? I can imagine a job lot of pistons also were also measured and size coded? At the final assembly of the engine the technician then only needed to match a #2 bore with a # 2 piston? No measuring required. If so I think this a rather clever way of accommodating upper and lower tolerances between pistons & bores from early days machining process.
Thanks
Bruce
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Ray Marloff
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Mar 1, 2015 02:37 PM
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Many of the B series engines left the foundry with sleeves. These blocks barely failed the test for proper thickness around the cylinder bores and a liner was fitted to rectify the problem. When a different marking is stamped next to a cylinder, this indicated that the cylinder is slightly larger than the rest and required a bit larger piston. It is very common to see this on motorcylce engines. When I send off the cylinders to be relined, they come back with a custom machined piston to match the newly installed and sized liner. RAY
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Mar 1, 2015 02:48 PM
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Dave....see picture..........
Law of Logical Argument - Anything is possible if you don't know what you are talking about.
"Anyone with an intense emotional interest in a subject loses the ability to observe it objectively: You selectively perceive events. You ignore data and facts that disagree with your main philosophy. Even your memory works to fool you, as you selectively retain what you believe in, and subtly mask any memories that might conflict."
Law of Logical Argument - Anything is possible if you don't know what you are talking about.
"Anyone with an intense emotional interest in a subject loses the ability to observe it objectively: You selectively perceive events. You ignore data and facts that disagree with your main philosophy. Even your memory works to fool you, as you selectively retain what you believe in, and subtly mask any memories that might conflict."
Speedracer
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Mar 2, 2015 07:29 PM
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In reply to # 2931549 by riley1489
Thanks chaps.
FWIW the block I show is not sleeved.
Bruce
FWIW the block I show is not sleeved.
Bruce
If it was, you would know it real quick, factory sleeves are cheap POS that hang out the bottom bores.
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