CAT 3126

[Renegade_Master]

I have vibration caused I believe by a miss fire. There is some black smoke, as you would expect, but more worryingly a bit of blue. So my friend says do a compression test.

Well as the injectors are to be found under the rocker cover, mechanically operated as per the valves, this means one cannot do a cmpression test, as you would on an older volvo, where you simply remove an injector.

If you cant do a compression then how does one find out the cause of the miss fire,I am at a loss.

 

[Latestarter1]

Neither CAT or Cummins recognise compression test a a valid trobleshooting proceedure. Which is why niether manufacturer publish any compression numbers.

Does not sound good. Something has happened and now you probably have one cylinder misfiring. You may be lucky and find something minor like an injector.

First thing I would do is pull the crankcase vent hose off the big canister behind the fuel pump. Crank up engine and see if blowby flow is puffing in sync with the misfire. Can also do this by simply removing oil fill plug. If so, likely piston/cylinder problem.

Next would be to take the rocker cover off and look at each valve, injector, rocker, and pushrods. Look for injector that is stuck down, pushrod out of position. If it looks ok, engine can be started with cover off. Look for equal motion of all rockers. Each injector can be manually fueled by pushing on rack. Misfiring injector will not change engine sound when rack is moved. Normal injector gives a hearty clank when firing extra fuel.

3126 is not a particularly DIY motor, it requires a number of special tools so even if the above does take you further you will probably need the CAT authorised service guy any way.

When were the charge air coolers serviced?

Good luck

 

[Renegade_Master]

Took head off one valve seat disintegrated, went to workshop spotted some hairline cracks, so heads useless. Just aquired a pre-owned one, now the fun starts to put it back together, valve clerances injectors to set up etc. Boats a working boat in the height of the season and been out of commission so far for 10 days : (

 

[Latestarter1]

CAT 3126 has a very colorful history.You will find many happy owners out there that have no issues what so ever, others owners have been plagued. Motor is especially sensitive to the installation. For example unless you are at least 10 Degrees front up, likely water will get back into the motor.

Two distinct reasons for valve failure on 3126. Inlet valves fail due to incorrect clearances. To set up the top end requires special tools about $2,500 last time we purchased the set, this price prevents many but the most specialised techs from purchasing the kit. Invariably proper top set does not get done. The goofy couch engineer who did the mid mount turbo arrangement must have been the same one who came up with the set up which required removal of the crank damper to change serpentine belt!

Exhaust valves fail across friction weld due to high exhaust temperatures. Unless motor can reach rated WOT plus at least 50 rpm. Overloading is never good, when you sea trial following repair make sure to pop a pyro in and record exhaust temperature. Anything over 510C at WOT and exhaust valves are working on the edge.

Modine charge air cooler must be overhauled every five years, three is better. and safer.

Do the job 100% right, which you no doubt will and you will have CYA!

 

[Renegade_Master]

thanks so much for that, will follow the instructions on valve clearance set up. Any tips on reinstallation of the injector/pumps ?

"required removal of the crank damper to change serpentine belt!"

you are right to change and adjust the rear belt is a bitch, just to get it over the flywheel. What do I have to remove (crank damper?) to aid this operation?

 

[Latestarter1]

thanks so much for that, will follow the instructions on valve clearance set up. Any tips on reinstallation of the injector/pumps ?

"required removal of the crank damper to change serpentine belt!"

you are right to change and adjust the rear belt is a bitch, just to get it over the flywheel. What do I have to remove (crank damper?) to aid this operation?

My internet access is poor at the moment, due to being hospital bed.

I do have 3116/3126 shop manual in pdf, however in Spanish, PM me next week if it is any use to you.

Simple reason crank damper has to come off is that damper is larger in diameter than serpentine alternator belt. I know of many installs where damper is nice and close to bulkhead, getting a bar on the cap-screws, makes for real fun.