low on power and hard to start help

[grizly]

oh hell , need some expertise..

i suspect valve spring weakness is causing the lack of power .
But i am usually wrong at times..
I have a DU 4U ,it was going great except it threw a fan belt ,by the time i noticed dam thing was boiling ..Then i also noticed the inlet manifold bolts had unscrewed and the thing was sucking dust and all..
Any how that is fixed now and i plus have orderd a new thermostat .Like i said it started well before ,the next day it was difficult to start .It is now difficult to start and is down on power.
I put my hand over the exhaust pipe when i crank it and it sucks and then blows..so i suspected a burnt valve obviously.
I pulled the head but the valves seem ok,even with diesel poured into the throats of the valves they dont really leak.But i can easily, or quite easily rock the valve springs across their base with my fingers ,with a little effort it isnt really hard ?? they seem too loose to me .Shouldnt they have a high seating pressure ?i think there is something wrong right there.
I also suspected a tight valve but i am really just guessing now as i should have checked that before i pulled the head.The head gasket seems fine,there is no coolant in the sump and it doesnt blow and oil out the exhaust ..

post edit..i just realised that i may have had to decompression lever on when i had my hand over the exhaust manifold,which would make it suck air ?


An help appreciated..
Thanks

 

[OldandWorn]

Check the compression. How long was it sucking dust?

 

[grizly]

hi
about a day ...

I didnt notice the raised manifold earlier because the bonnet hides it quite well...it was basically the next morning when she was cold ,that i kept cranking to get it up..Cranking more trhan usual...now i use ether ,a quick hit as it goes...but i have noticed less power..
There is a fine film of dust in the intake manifold ports,i am pissed off i hadnt tightened these bolts enough..
There is no ridge on the liner ,maybe the rings are on theyre way out...

 

[OldandWorn]

Well, I would check the compression as the next step. I don't have the expertise to comment on the valve spring tension but it shouldn't take much to hold the valves closed on a slow reving engine. If the decompression holds the exhaust valve open, than yes, the exhaust wouldn't feel normal.

 

[Wick]

How many hours has the engine done? how much blowby does it have ? When you say boiling how hot did it actually get ? did it blow all the water out ? if it got hot enough it may have taken some tension out of the rings, having been dusted as well the combination of these will severely shorten piston ring and an engines life, valve spring tension won't be your issue. You will obviously need the head back on to do a comp test so I would suggest that if you plan to use the machine on a regular basis and since you have the head off, may as well drop the sump, pull a couple of pistons & check the rings.
Alternatively if you don't use it much and can't justify a rebuild whack the head back on and put up with the lack of power and giving it a sniff when you cold start it and keep drivin' her.
hope this helps

 

[ben46a]

Sounds like low ring tension and wear. Check the compression. Is there any visible crosshatch on the cylinder walls? Or scoring?. I'm thinking a hone and re reing is in order. Or you could try the old bonami trick to re seat the rings, but that won't help if they've lost they're tension. Valve springs wouldn't cause this issue unless they're majorly out of adjustment.

 

[Old Magnet]

One more thing to check....
Do the hand over the exhaust check again (under compression). If it still alternately sucks and blows, check the exhaust heat exchanger in the intake manifold.....they are known to rot out resulting in a big vacuum leak.

My memory's a little off. Check should be done by holding a piece of paper over the pony exhaust when the main is running. Would also show up while cranking the main (main exhaust).

 

[grizly]

the head is off so i cant test it..
It was pissing wtaer out the radiator, i was in a bulldust situation and i didnt see it till it was done ...the temp gauge went to over 100c dg but luckily there are no coolant leaks internally...it had lost some water probably 1 --2 litres the hour
meter shows 8259 H ,i bought this dozer 5 months ago and dont know the hsitory of it.the other thing is after all this happened you can see a presure of air mixed with a dusty pre cleaner jetting out of the plastic pre cleaner bowl of the intake.Because it is right in my face when i am driving you can notice it but it isnt severe ,but with the dust you can see it..a light puff kindof a jet of dust..

 

[grizly]

i work this thing and need the power so i may re ring it with new pistons .the liners have some minor distortion .

 

[grizly]

so today i pulled the sump off (a job eh) and ripped the pistons..All looks good ,the oil rings area bit pitted so i sourced a set of rings for 200 bucks..I noticed something scary ...no i can move the crank (slightly)by forcing it upwards with my arm..it has a slight squishing sound of the oil coming out of the main bearings.So i flexi gauged it ,trun out it has 8 thou which surprised me...I was thinking way more if i can physically see it move with a keen eye...Good news is ,There are no scores on the crank journals at all ,it looks smooth and i am happy about that .The main bearings have no sizes on them ...The oil pressure cold was around 29 psi and hot it fell to 22 psi .I had a 50% mix of oil stabiliser in there just for insurance which is allowable accrdin to moreys (brand) So 6 litres of moreys and 6 of the normal stuff.
I was lucky to get these bearing as they weer avilaible only from the USA ,thats what everyone said i contacted ,except one bloke who is relentless and finally got a tip off down QLD way ...should be here Saturrday hopefully or tomorrow..

 

[grizly]

One more thing to check....
Do the hand over the exhaust check again (under compression). If it still alternately sucks and blows, check the exhaust heat exchanger in the intake manifold.....they are known to rot out resulting in a big vacuum leak.

My memory's a little off. Check should be done by holding a piece of paper over the pony exhaust when the main is running. Would also show up while cranking the main (main exhaust).

will do ...