Hello. I have a blown head gasket for starts. Am wanting to check for markings on finding TDC on the engine. Where do I start to look while trying to see under all the paint. I have searched the questions and understand some boats are not marked....... And that you can get close by using valves and the squit of fuel from the injector.... Just want to try this before starting.Thanks for all your help.Dale
Finding TDC on MD6A
- Thread starter semi.retired
- Start date
First I would say it's almost impossible for the engine to get out
of time. The gears driving the high pressure fuel pump would have
to break a tooth or the they would have to be very badly worn or
maybe the gear bearings. I would suggest that the head bolts needed
to be re torqued down before the head gasket was blown. I guess if
there is damage to the gears the timing could be off. I have never
seen that happen and I have worked on some diesels. If I had worn
the engine out rebuilt it and wore it out a second time I misuspect
a problem with the timing gears,
--
Doug Pollard
Albin Vega Sea Legs 2225
KK4YGO
On 05/22/2014 12:28 PM,
semi.retired@... [AlbinVega] wrote:
of time. The gears driving the high pressure fuel pump would have
to break a tooth or the they would have to be very badly worn or
maybe the gear bearings. I would suggest that the head bolts needed
to be re torqued down before the head gasket was blown. I guess if
there is damage to the gears the timing could be off. I have never
seen that happen and I have worked on some diesels. If I had worn
the engine out rebuilt it and wore it out a second time I misuspect
a problem with the timing gears,
--
Doug Pollard
Albin Vega Sea Legs 2225
KK4YGO
On 05/22/2014 12:28 PM,
semi.retired@... [AlbinVega] wrote:
Douglas thanks for the reply. More info.... This all started because the #2 cylinder is not firing... Then we noticed the blown head gasket. Also there is excessive fuel in the exhaust when the motor is started up. There are also pic of the gears with some teeth missing... These pics are from the second previous owner. We are assuming that the gears were fixed. Also notes in the repair manual where the injector pump timing is talked about.The mechanic working on this assumes the same as you.... That the head was never retorqued and the gasket blew. The fuel is from possibly excessive cranking before motor starts. After the motor is warmed up the problem stops. Also when I motored her here after buying her she could do 6 knots. There were no oil leaks... Did not seem like a loss of power was involved.THIS. LEADS ME TO ALSO ASK CAN A VEGA DO OVER 5 KNOTS ON 1 cyclinder. I don't remember if after warming up if both cylinders were firing. The plan is to pull the head replace the gasket. Since we are not sure if the injector timing is right we need to find TDC. To check the injector timing. If the injector is the problem can get it rebuilt for about 300$ US plus parts. Also both injectors were tested and both worked.When we pulled the back injector it looked very dry. Yet it tested good.Everyone's help is appreciated.Thank youDaleHull 1877Laughing Gull
Douglas thank you for the reply. More info. Yes my mechanic agrees with you that he thinks the gasket blew because the head was never retorqued after the install.This all started because of the 2nd cylinder was not firing upon startup. Also there is excessive fuel in the exhaust upon starting up. We also have pics taken back in 2000 that show damaged gears. We are assuming they were fixed. We are also making the assumption that the excess fuel is from excessive cranking because of blown head gasket.Also have note in maintenance manual that shows they were working on the injector timing. So maybe it was installed a tooth off. We just don't know yet.Also on her initial,voyage here about 25 miles Laughing Gull did achieve a speed of over 5 knots. This was during slack tide and then about 6.9 with tide. So my second question is can a MD6A achieve this speed on only one cylinder. I just don't remember if the second cyclinder fired up after warming up.Our plan is to pull the head Friday then we can look at the internals. We have already had the injectors checked and they tested fine. We did think that the #2 injector was dry and not firing. After getting the head gasket fixed we can move on to the next step.The injector shop said they can rebuild the injector pump for about 300$ US plus parts if we need to go there just won't know until the head is pulled and looked at. Also thermal imaging showed no problems in either cylinder no damage or overheating on the internals. To the best of the surveyors knowledge. All help and thoughts on this problem is appreciated.Thanks,DaleLaughing Gull Hull 1877
I would say this if there were a slight leak in the head gasket it
may well be she would be slow starting and could pump fuel into the
exhaust and only run on one cylinder, It is also possible at higher
or near or at Maximum Rpm the piston might be coming up fast enough
to generate nearly full compression and she may well be able to run
six knots. If the engine compression , fuel and air mixture is
right you should be able to open the compression release crank her
over about two or three times winding up the flywheel fairly fast
throw the compression release shut and she should fir an run the
first time the cylinder goes over top dead center. When starting
with the starter she should start the first time the starter pulls
her over top dead center. IF you had a broken ring pull the hose
off that goes from the valve cover to the air filter, She would
likely be blowing smoke rings out of that 3/4 inch diameter hole.
If you had taken the engine completely apart the timing might need
to be set by loosening and rotating the high pressure pump. Once set
it should be correct from then on. I would replace the head gasket
and maybe lap the valves with lapping compound. Your mechanic will
have no trouble doing that. If She had been running on one cylinder
she was likely blowing black smoke from that cylinder. Lapping
should take care of any minor damage done to the valve seats bu
carbon smoke. I really would think that if you replace the gasket
and start her up and she should run well. Even if the timing were
off a little it is likely she would just smoke some then you might
worry about timing her. I can't imagine you have been running her
with a broken tooth I would think the timing would be so far off she
would not run at all. I have never seen this, so if someone knows
about this please correct me.
--
Doug Pollard
Albin Vega Sea Legs 2225
KK4YGO
On 05/22/2014 05:41 PM,
semi.retired@... [AlbinVega] wrote:
may well be she would be slow starting and could pump fuel into the
exhaust and only run on one cylinder, It is also possible at higher
or near or at Maximum Rpm the piston might be coming up fast enough
to generate nearly full compression and she may well be able to run
six knots. If the engine compression , fuel and air mixture is
right you should be able to open the compression release crank her
over about two or three times winding up the flywheel fairly fast
throw the compression release shut and she should fir an run the
first time the cylinder goes over top dead center. When starting
with the starter she should start the first time the starter pulls
her over top dead center. IF you had a broken ring pull the hose
off that goes from the valve cover to the air filter, She would
likely be blowing smoke rings out of that 3/4 inch diameter hole.
If you had taken the engine completely apart the timing might need
to be set by loosening and rotating the high pressure pump. Once set
it should be correct from then on. I would replace the head gasket
and maybe lap the valves with lapping compound. Your mechanic will
have no trouble doing that. If She had been running on one cylinder
she was likely blowing black smoke from that cylinder. Lapping
should take care of any minor damage done to the valve seats bu
carbon smoke. I really would think that if you replace the gasket
and start her up and she should run well. Even if the timing were
off a little it is likely she would just smoke some then you might
worry about timing her. I can't imagine you have been running her
with a broken tooth I would think the timing would be so far off she
would not run at all. I have never seen this, so if someone knows
about this please correct me.
--
Doug Pollard
Albin Vega Sea Legs 2225
KK4YGO
On 05/22/2014 05:41 PM,
semi.retired@... [AlbinVega] wrote:
Also do you have engine manual? I think it shows a timing mark in a
window on the flywheel housing where the pump connects to the
housing. I think you can download a manual as a PDF file on Line??
--
Doug Pollard
Albin Vega Sea Legs 2225
KK4YGO
On 05/22/2014 05:41 PM,
semi.retired@... [AlbinVega] wrote:
window on the flywheel housing where the pump connects to the
housing. I think you can download a manual as a PDF file on Line??
--
Doug Pollard
Albin Vega Sea Legs 2225
KK4YGO
On 05/22/2014 05:41 PM,
semi.retired@... [AlbinVega] wrote:
I must have read your post too fast as I did not catch that the
injector was dry. That seems to fly in the face that there is fuel
puddling in exhaust. The fact that the injector is dry would seem
to indicate that it is fireing. If it wasn't injecting fuel you
would not have excess fuel in the exhaust. I can't help but suspect
that the cylinder is not fireing at slow start up or idle speeds but
then starts firing at higher speeds and so dries the injector
out??? It is possible that the pump is worn on that cylinder and
so does not reach the 2800 lbs pressure needed to inject fuel. ( not
sure that is the correct pressure as I am writing from memeory)
Running at higher speed it does supply enough pressure to fire the
cylinder. This could account fore the boats speed which seems to me
too high for the engine to be running on a single cylinder. There is
certainly some mystery involve there.
--
Doug Pollard
Albin Vega Sea Legs 2225
KK4YGO
On 05/22/2014 06:14 PM,
semi.retired@... [AlbinVega] wrote:
injector was dry. That seems to fly in the face that there is fuel
puddling in exhaust. The fact that the injector is dry would seem
to indicate that it is fireing. If it wasn't injecting fuel you
would not have excess fuel in the exhaust. I can't help but suspect
that the cylinder is not fireing at slow start up or idle speeds but
then starts firing at higher speeds and so dries the injector
out??? It is possible that the pump is worn on that cylinder and
so does not reach the 2800 lbs pressure needed to inject fuel. ( not
sure that is the correct pressure as I am writing from memeory)
Running at higher speed it does supply enough pressure to fire the
cylinder. This could account fore the boats speed which seems to me
too high for the engine to be running on a single cylinder. There is
certainly some mystery involve there.
--
Doug Pollard
Albin Vega Sea Legs 2225
KK4YGO
On 05/22/2014 06:14 PM,
semi.retired@... [AlbinVega] wrote:
When I would start the Volvo it would start on one cylinder, especially after winter layup. The problem was air in the injector fuel lines and the injectors would have to be bled individually as well as the lines leading to the injector pump. The fuel tank is below the and there is a propensity for the fuel to pull air into the system as gravity is pulling on the fuel. There is info on this subject in the old messages where some people went as far as moving the tank to a higher position to eliminate this problem. The tank being higher than the rest of the fuel system makes the fuel positive pressure and air is not sucked into the fuel lines. JimVegabond 1870Wickford, RI