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Old 26-08-2017, 12:05   #1
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Volvo penta Md7a reseating valves ,and replacing valve seals only 2? A few questions.

I have a 1977 volvo md7a was smoking badly. I pulled the head off had lapped the valves and I'm gonna replace the seals there was only 2 seals, one on each of the bigger valve stems which are on the intake valves.the is there supposed to be seals on the exhaust side too? I can't imagine the disintegrated but figured I'd ask. Also does any one know where to find these seals the Volvo penta store exploded diagram isn't showing them. The numbers on them are;860 n w 8-12/15.5-9.5 b 60 e 41.
I also lapped the valves I think as best as they will get now the top of the valve will be touching before it seats it's pretty smooth the exhaust valve still have a tiny bit of pitting I'm gonna attach a pic. And hopefully some one can tell me if they are good enough as is or if I have to take a little off the valve to let it seat deeper, thus allowing me to lap a tiny bit more.
And seems pretty hard to find or indentifymy injectors. The exploded diagram is showing 2 diff injector types but I don't think either are mine. I have Bosch Kbal65p 1/4 882 .any one know a source? I'm gonna have them tested, but I'm preparing to buy 2 new ones any way. Thank you. And My Md7a has a serial #12759
Well sorry guys I have a few more questions while we're at it. So I removed the lift pump and since then I have turned the fly wheel a bunch of times. Is that gonna effect my timing or is that lift pump not associated with timing?
And last but not least I'm not sure if my exhaust manifold is the original or if the p.o replaced it with one off a md6 or a variation of one or the othe but in the pic on the head you can clearly see there's a round hole in the middle that is gasketed and nearly clogged I don't see where it even goes to? But on the manifold I can't tell if it's just clogged with carbon or if it's a knock out plug I hit it with a pic seems pretty solid before I get buck wild on it does any one have this port on theirs? I know there's a few diff manifolds made because when I was looking at diagrams for my raw water piping mine was not the set up that was shown for my model. My thoughts were possibly this is a retro fit or perhaps I'm wrong?
That's a lot of questions thanks for your help. I've seen the exploded diagrams at marine parts Europe and Volvo penta shop and seems mine don't match up 100%. For example in the picture with my fingers pointing to the 2 water passages I replaced the head gasket in the past and I can't remember which one( I discarded the old head gasket) but one of them holes didn't match up it was slightly off. And it was a quality gasket from the Volvo penta store made in Sweden?
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Old 26-08-2017, 12:29   #2
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Re: Volvo penta Md7a reseating valves ,and replacing valve seals only 2? A few questi

Here's a better pic of the mystery port to no where I sprayed some we in it and it's actually art of the raw water passages in the head but yet on the exhaust it's just a knock out plug...? Any ideas here's a better pic all the screws and straws are water passages that drain into that hole. Now I've been running the motor with that manifold for 2 yrs with no over heating problems so I'm kinda at a loss here.
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Old 26-08-2017, 12:35   #3
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Re: Volvo penta Md7a reseating valves ,and replacing valve seals only 2? A few questi

You only need a seal on the intake valve. It keeps the oil leak into the engine to a min. The exh goes the other way, so no big deal.
The only test you can do with your valve lapping job, is pour a fluid into the intake port and see how much leaks out past the valve. No leakage is the aim but I really doubt you are going to make that. If you want to cheat use water as it doesn't leak as quickly. Diesel is what you should use. No leakage for 25 sec is the limit. If you get anywhere close, whack the valve with a rubber hammer a bunch of times as that sometimes helps seat the valve.
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Old 26-08-2017, 17:16   #4
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Re: Volvo penta Md7a reseating valves ,and replacing valve seals only 2? A few questi

Ok thanks. So your saying put the springs and all back together pour diesel into the top and at a minimum I should have 25 seconds w not a drop? And your saying it's hard to get them to toatally seal? Is that BC the way the valve is tapered as to where I noticed the top edge of the valve will seat before the bottom wil seat if you keep grinding? What is the remedy for this I saw on the exploded diagram there is a part called a valve seat. valve seat, exhaust 3875346 .thats the part I'm not sure how that is installed have you seen these?
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Old 26-08-2017, 18:00   #5
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Re: Volvo penta Md7a reseating valves ,and replacing valve seals only 2? A few questi

Installing a new valve seat is a big deal. Sorry to say, just lapping valve seats is a half ass deal. It is impossible to get a proper fit by lapping. Valves and seats are ground at different angles. Lapping is only done after grinding to get a perfect seal.
In a proper OVHL, valve height is the big deal. The best way to get it correct is to use new valves, not new seats.
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Old 26-08-2017, 19:51   #6
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Re: Volvo penta Md7a reseating valves ,and replacing valve seals only 2? A few questi

The original valve guide seal, part number # 833347 was an umbrella type that sat on the top of the collet and keepers, and was used only on the inlet valves. This number was replaced by valve guide seal #1306630. In the MD7B this replacement number was used on all four valve guides.

It doesn't matter if you rotate the crankshaft with the fuel lift pump removed from the engine. The lift pump doesn't have anything to do with the injection timing.

Never heard of the holes in the head gasket not matching up correctly, but you have to be sure that you have the gasket right side up....it can be installed upside down.....look at it both ways.

Leave the freeze plug in the manifold alone.

DougR
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Old 26-08-2017, 22:24   #7
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Re: Volvo penta Md7a reseating valves ,and replacing valve seals only 2? A few questi

Ok thanks for the responses..still getting a grasp on the lapping process. I used the suction cup and grinding paste from permeates in the pink tube.do I need to get a finer "lapping" paste to finish them,after using the grinding paste?Only saw grinding compound no lapping compound. Is a perfect finish obtainable if I were to take to a shop, if that's possible is it worth it?
So that's a freeze plug not a mis matched manifold. Good to know thank you
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Old 26-08-2017, 23:10   #8
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Re: Volvo penta Md7a reseating valves ,and replacing valve seals only 2? A few questi

Seems there's 2 diff head gaskets for the md7a
head gasket 840270 is 1.3 mm
The other is 840910 is .8 mm
Any input on which would be the better option?
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Old 27-08-2017, 00:49   #9
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Re: Volvo penta Md7a reseating valves ,and replacing valve seals only 2? A few questi

Those seats are pretty bad. If you don't get them done properly, you'll just be pulling the head again in a few hundred hours. Seat should be smooth. No pits. With the pits you have, you'll end up burning a valve.
Hand lapping was common for gas engines decades ago in road side garages. It was done when head machine shops were far away. Diesels have higher temperatures and pressures.
When closed, the valves need to be at the proper height. If they sit to far into the head from too much grinding it reduces the compression. Sometimes enough to make a hard starting engine.
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Old 27-08-2017, 01:14   #10
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Re: Volvo penta Md7a reseating valves ,and replacing valve seals only 2? A few questi

iT'S NOT AN OPTION, it depends on your engine number as earlier or later model as

1.3 mm is engine numbers up to 35144

and

0.8 engine number from 35145 up

If you dont know your engine number measure your old gasket to get an idea

Cheers Steve
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Old 27-08-2017, 02:02   #11
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Re: Volvo penta Md7a reseating valves ,and replacing valve seals only 2? A few questi

Would like to add some further input as to some comments previously posted for factual information as

1) The faces of most valves are ground at an angle of 45 to the Valve-stem, although angles of 30 have been used for some intake valves. In some engines, that intake valves have 30 face and angles and the exhaust valves have to 45. The valve seats are often ground to the same angle as the valve face, but some manufacturers use an interference angle. With this the valve-face and seat are ground to slightly different angles. This Vary with different engines and the interference angle may be 0.5 or as much as 2. A typical specification is 45 for valve at face and 44 for the valve seat

2) The interference angle is provided by an engine manufacturer to allow for quick bedding in off the valve face to the seat on new engines, and is commonly NOT used when reconditioning valve and seats.

3) The purpose of grinding is to have the valve and valve seat make an air-tight fit. The purpose of lapping is to see if that was done correctly and "fine tuning". If your heads were rebuilt at an engine shop, the valves had a machine put a precise bevel on the valve and seat surfaces, but a good seal is not guaranteed - a good engine builder will always check everything before final assembly. If the valve seat and face were ground correctly, the lapping process should take a minute or less for each valve.

4)It actually takes longer to clean, prepare, and round up the supplies than to actually lap the valves.

5)Once the valve is in the head, the next step is to wet the suction cup on the lapper and stick it on the valve face. Once the lapper is grabbing the valve, you begin the lapping process. Place the lapper in between both hands, and using light pressure, rotate the tool back and forth at a moderate pace. The motion is similar to starting a fire with two sticks.
Lift the valve up periodically and rotate it 180 degrees to ensure the grinding compound is getting evenly spread. You'll want to watch the progress - you're looking for a consistent grey ring on the valve and valve seat with no breaks or high spots.

6)When you can feel and hear the compound losing its cutting ability, wipe off and check. Both faces should be a dull grey when you're done, with an even width across both faces.(this doesn't have to wide) or does not have to be in the middle of the valve, just an even ring around the valve. You will see the same consistent gray line on the valve and the seat.

7)It is not necessary or good to over-lap the valves. It is unlikely, but possible, to remove too much, and doing so will ruin the valve seat. If you are unable to achieve a consistent grey ring, the seats are probably worn out and will require professional cutting.

8)Make sure you remove all the valve-grinding compound, it is highly abrasive and could harm your engine.

Cheers Steve
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Old 27-08-2017, 04:19   #12
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Re: Volvo penta Md7a reseating valves ,and replacing valve seals only 2? A few questi

The seats in your photo look pretty dodgy - it should not cost too much for the local head shop to look at them and suggest a course of action. False economy to try grinding in as you are doing.

Regards,
Richard.
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Old 27-08-2017, 06:19   #13
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Re: Volvo penta Md7a reseating valves ,and replacing valve seals only 2? A few questi

Ok guys thanks for the input. I guess. Will take the to a diesel shop have them tell me best cours of action to take.....is it ever easy? Or cheap? Haha wishful thinking. I have found my serial number is 12759 so I will be using the 1.3 mm gasket. Any clues on the injector identification? The numbers Bosch numbers kbal 65p 1/4 882 060 aren't coming up on google searches I've made no progress with the injector identification..
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Old 27-08-2017, 08:48   #14
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Re: Volvo penta Md7a reseating valves ,and replacing valve seals only 2? A few questi

OK- here you go Injector cross reference news,

As yours is an early MD7A the original Volvo part number was 838153 this was replaced by the new and still valid part number as 838289 available at Marine Parts Express for the lovely price of around $400 each !!!!,

The Bosch part number for that injector IS 0 432 191 861 and the web link to that is 838289,VOLVO 838289; Injector where you need to email them for the price,

Cheers Steve
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Old 27-08-2017, 08:53   #15
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Re: Volvo penta Md7a reseating valves ,and replacing valve seals only 2? A few questi

Also another link to cross reference and company selling spare parts for bosch injectors that i find useful at times
nozzle holdes,diesel fuel injection,fuel injection pumps,diesel pump,plunger,nozzle

Cheers Steve
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