Jump to content

Engine vibration/juddering


Featured Posts

Isuzu 35 engine has been firing well for years, runs smoothly at all revs. Just recently at cruising speed, 1000 revs the engine soundis as though it's judering, t does not do this at 800 or 1200 revs. I filled with fuel about 30 hours engine time before the judder started. Have checked engine mounts and they seem fine. Filters changed about a month ago. When I run engine out of gear the judder is far less pronounced, no air filter in this type of engine...any ideas?

Link to comment
Share on other sites

In my experience there are two main reasons that cause engines to judder,  muck or air in the fuel or engine mounts.  The latter tends to be more noticeable at lower revs.  Although you say you have checked the mounts, then can show little symptoms even though the rubber has softened.  One sign is a slightly sticky black residue round the mount, which is caused by the mount overheating due to excessive movement.  Not to be confused with a similar residue that can be caused by a failing alternator belt.

Link to comment
Share on other sites

5 minutes ago, dor said:

In my experience there are two main reasons that cause engines to judder,  muck or air in the fuel or engine mounts.  The latter tends to be more noticeable at lower revs.  Although you say you have checked the mounts, then can show little symptoms even though the rubber has softened.  One sign is a slightly sticky black residue round the mount, which is caused by the mount overheating due to excessive movement.  Not to be confused with a similar residue that can be caused by a failing alternator belt.

Will check the mounts again and come back, there isn't an air filter.

Link to comment
Share on other sites

11 minutes ago, umpire111 said:

Will check the mounts again and come back, there isn't an air filter.

Ok, tested mounts again by putting large screwdriver underneath each and lifting, also checked bottom nuts, seem ok. Also no deposits around rubber mounts. Not sure where air intake is

Link to comment
Share on other sites

3 minutes ago, umpire111 said:

Ok, tested mounts again by putting large screwdriver underneath each and lifting, also checked bottom nuts, seem ok. Also no deposits around rubber mounts. Not sure where air intake is

On our Isuzu 33 it is on the side of the rocker cover next to the header tank. 

Link to comment
Share on other sites

2 hours ago, Tony Brooks said:

Either that or mounts. Check the small bolts that secure the mount to the bed as well as the large nuts.

I suppose it just might be a valve clearance thing so check those a swell to be sure.

Mounts no problem but valve clearance beyond me

Link to comment
Share on other sites

Is this any help?

Adjusting valve clearances

There is only one method that is applicable across all engines whatever the number of cylinders and the valve layouts and although it takes a bit more time it is the one I prefer to tell boaters to use.

You need access to either the front crankshaft pulley (the lowest one the belt is on) or the flywheel but on a Kubota it would be the pulley.
 
Using the big nut on the crankshaft pulley (see later for a tip) turn the engine in its normal direction of rotation until one valve is fully down.
 
Use chalk or a white board marker to put a mark on the pulley.
 
Turn the engine ONE complete turn so the mark is more or less back where it started. You do not have to be exact and I suspect an inch either way will do.

Now adjust the valve that was down, rub out the mark on the pulley and mark that rocker as having been done.

          
Front rocker fully down    Mark on pulley & bolt head    Feeler gauge in gap for adjustment
 
Turn the engine again until the next valve is fully down and repeat the above. The next valve down will appear to be random so that is why you need to mark or note those you have adjusted.
 
The reason this works is because the camshaft turns at half the speed of the crankshaft so if you think of a cam as a slice through a boiled egg when the valve is fully down (open) the pointy end of the cam will be pointing straight up. If you then turn the crankshaft one full turn the cam will have turned half a turn so the pointy end of the cam is now pointing down and the pushrod (in effect) is sitting on the lowest part of the cam. The lowest part of the cam usually is in excess of 30 degrees of rotation so that means absolute accuracy in the "one complete turn" bit is not needed.

If whoever is doing this job is looking back to cars of 60s & 70s (or before) please be aware that in those days the valve springs were very strong so it was hard to pull the feeler out having tightened the adjustment so much a valve would be held open. Nowadays the springs are far weaker and it is all too easy to get a feel on the gauges as was used long ago but now it will have over tightened the adjustment and may even hold a valve open, you need a really delicate feel. Also remember that valve clearances that are too slack will not damage the engine, ones that are too tight can. Slack ones just clatter.

Now the tip but please remember this is considered bad practice and can lead to a failed alternator belt (usually it doesn’t). In most cases it is easier to get a spanner or socket onto an alternator pulley nut so start to turn the alternator and note that one side of the belt run goes tight while the other side goes slack. If/when the belt slips on the pulley simply press in on the slack side to take the slack out of the belt.

 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.