Volvo Diesel Question

[GeorgeH]

Should I be able to hand turn my MD7B?

Today when winterizing I noticed I can turn the flywheel by hand through several turns and it never feels like the compression stroke will stop my hand turn.

I've had some problems with overheaing this past season (the engine slowly goes to into the red zone then drops into green and then starts creeping up again). But the engine starts up quickly, it doesn't burn oil or use excessive fuel.

Seems to me that the compression stroke should stop the hand turn.
GH

[Steve D]

Does not sound good to me. Diesels usually have a compression of 10:1 at a minimum.

[Jerry Hammernik]

I can turn my MD7B by hand. I feel a resistance at the compression stroke but I can still turn it. It runs fine and has always been this way in the years I have had it.

[vandyman4]

I have a '64 Land Rover that I put a 200TDI from a discovery in and I can use a wrench and bar the engine over so I would say yes you should be able to turn it over.

[Maine_Buzzard]

The compression is 17:1. You should hit a compression stroke and have the flywheel bounce back because of the high compression. I have a hand start handle and even when cranking a spare engine with the compression lever up, getting it to speed, and tossing it down, I don't get it through TDC. No way I could.start a 7 with the handle.

Do you hear air leaking as you turn it over? At least two out of eight half revolutions should be very hard.

[Neil Gordon]

George,

I had the same issue with my MD7A... temp would rise to the red, then there would be a puff of steam from the exhaust and the temp would drop down. The cure was removal of the manifold and thermostat housings and cleaning/reaming as much gunk and other buildup as possible.

[Klem]

Do you have the compression release activated? Are you doing this extremely slowly? If not, something doesn't sound right. Spinning the engine over by hand, you are essentially hand cranking an air compressor and you should be able to feel the high pressure air resisting as you get near TDC. The only reason that you would not be able to feel resistance is if there is no high pressure air due to either really poor sealing or waiting long enough so that your good seal will leak. Sealing occurs on the piston rings and the valves.

If the engine starts well and runs well without any blue smoke, I would tend to just ignore it. How good of an air compressor the engine is at really low speed is not what is important, what matters is how it works as an engine.

[Kevin Kaldenbach]

I would not worry about being able to turn the engine over by hand. I have turned large diesels over relatively easily. This is why: a diesel engine requires that it turns over rather fast when you are starting it. One reason for this is that if it turns over slow some compression will be lost past the rings before the piston gets to the top of the stroke. Imagine how much compression gets lost as you roll the engine over by hand. Most of it. Your engine most likely is no spring chicken so is a little looser then when it was new, but if it starts relatively easy and runs like it should then leave it alone.