Caterpillar Scraper Apron Link and Pin Holes

[621_Rocker]

Why is there two pin holes on Caterpillar aprons? Which pin hole is the aprolink supposed to be pinned to? Is the apron link supposed to be straight or have a curve in it? I am working on a 621(A) that is pinned in the bottom apron hole. It has a receptacle on the bottom hole for the pin ear. The link is not straight. It has a curve in it and a slight twist. The apron does not fully close with the banana are fully down. I have seen other Caterpillar scrapers pinned in both the bottom and top pin holes and with straight and curved links. I have been planning on trying to straighten the link. I would like to find out what others know about this or their opinions.

621 Rocker

First two pictures are of the machine that I am working on and the other is of a 627G.

 

[Gavin84w]

Rocker,

First up, the 2 pin holes allow for options depending on the material you are working, it can also assist with getting the banana up top lower for transport.

The link to it should be straight, i would say that non factory deflector that has been welded on the front of the apron suffered from all the planets aligning one day when a rock got between things while closing the apron, cut it off and put it back to the way Cat designed it, thousands of others without it dont suffer that problem. The bent link in the bottom hole would be exagerating the full non closure, run it in the top hole unless you need it in the bottom.

Would be good to see some pics of the whole machine, they are a classic motor scraper, does she still have the D336 V8 in her?

 

[621_Rocker]

Gavin,

Pictures in my service manual show the bottom hole being used. I am going to try to straighten the link and then try out the bottom hole. If it does not work then I will go to the top. I was thinking that the deflector is factory but maybe I am wrong. I have seen other links with curves to them. In looking at the apron I don't think that it is too difficult to imagine an operator getting a heaped load and then having a rock fall over the top and getting trapped above the bottom of the link and then the next cycling of the apron the rock becomes wedged as the link is lowered again with the down force causing the link to be bent. If the link is in the upper pin hole there should be a little more down force on the apron.

This machine, a later 23H, has the D336 V8 in it. I will provide some pictures later. The engine was rebuilt and then sat in the shop for 5 or 6 years and has now just been installed. I have replaced about every seal on the machine with the exception of the cylinders. I have another 23H that has been updated to a 3306. Cat put out an update kit for this. I have not been around a D336 before but have been told to avoid them. It must have been quite the engine for there day when they first came out having dual overhead cams and a large number of timing gears on both ends of the engine. My 3306 sure takes up a lot less room than the D336. Did they use it in very many OTR trucks? Must have had a lot under the hood room for it or do you guys in Australia call it a bonnet?

621_Rocker

 

[Gavin84w]

With using the top hole there is less chance to bend the rod as it is further "up" when you have the apron down if you know what i mean. Many of Cats service manuals are developed in an environment that is another building off from the assembly line so the pics are not always the best guide to go by. The downforce is a function of hyd pressure and there is no real mechanical advantage to change that from hole to hole. If you are in real sticky mud you dont need to close the apron all the way to the cutting edge as the mud will hold itself in but you may need a bigger opening to push it out so the lower hole helps there.

The D336 was only used in the 621, no other Cat machine had that little screamer.

Bonnet/hood we use both down here.

 

[StanRAUUS]

Parts are scarce for 23Hs, example Trans drive shaft & gear. V8 336 great example complexity versus simplistic in-line 6cyl 3306
Enjoy your’ Toys!:notworthy

 

[621_Rocker]

Gavin,

I agree with you that the top hole has less of chance of having the link bend. I disagree with you as far as a difference of mechanical advantage. Think of a piston pushing down on to a crankshaft via a connecting rod. The piston wants to push straight down. When the crankshaft throw is at the 3 o'clock position the crankshaft best accepts the downward force from the piston. As the crankshaft approaches the 6 o'clock position it needs more horizontal force so the mechanical advantage of the downward force from the piston is reduced as it is translated more in to horizontal force as the crankshaft throw approaches the 6 o'clock position. Same situation here with these two pin holes although they are a lot closer together than 3 o'clock and 6 o'clock and the difference would not be great.

The D336 was used in the 621, 621J, 980, as well as a marine and industrial version. The D336 was known as a 1676 for a truck engine. I believe the equipment version was rated at 300 hp and the 1676 was rated at 340 hp. Information that I just read says that Caterpillar sold them with a 200,000 mile warranty and that many ended up being replaced with 1693 engine. The replacement kit that they made for replacing the engine with a 3306 in the 621 produced 270 hp I believe. Apparently they made good power but did not have long term reliability and were oil leakers.

For further information you can read the American Truck Historical Society posting at: http://forum.aths.org/PrintTopic143620.aspx
(the next to last post By garymac is the most informitive)
and http://discuss.ibdozing.com/discus/messages/2/164.html?1296444595

StanRAUUS,

After working on two 23Hs I have not had too much difficulty obtaining parts yet.

621 Rocker

 

[Gavin84w]

I don,t think the piston in an engine analogy is an apples for apples comparison, there is a thing called a flywheel and usually other pistons that help balance that show out. The relief valve will be set at a certain psi and when that is sensed via the resistance to move the apron any further down it will stop pushing and it will not discriminate on what position the apron link is in.

The apron is not designed as a guillotine and requiring any mechanical advantage to close down with any more force than the hyd system can supply

Here is the wording from a 657 operation manual on what the holes should be used for:

"Use the lower hole to permit wider apron opening. Use this position for heavy material" and "Use the upper hole to allow the apron to be closed fully. Use this position for hauling sand or other loose material"

Forgot about the old 89P 980 and a J621 to me is the same as a 621, well at least the end where the engine is.

 

[621_Rocker]

Here are some pictures for you Gavin. I will provide more later.

 

[tctractors]

Rocker, years agoI was on a site with some 627's firing about, the muck was an absolute pig to handle going into the scrapers in big hard chunks, this would some times cause the apron to go right up and over centre itself locking itself up, the pin plate on the apron was bolted on?? not welded.

 

[StanRAUUS]

Rocker,
Cleaning desk out, found Special Instruction - Installation of 8N6332 Engine Arrangement From SMHS7551
621 - 23H, 15U / 623 - 52U

 

[621_Rocker]

StanRauus,

Could I get a copy of those installation instructions from you? My parts guy could not find any listing for the my engine serial number on the 3306 of my other rig. He said that he had never ran in to anything like that before and he had been working the Cat parts counter for years. I took him a photo of the serial number plate. The service parts guy who is a bit of a Cat guru came up with a parts listing for the 3306 arrangement for the 621(A).

Thanks,

621 Rocker

Here are some more pics of the 621 I have been working on:

 

[621_Rocker]

More 621 Pictures

 

[621_Rocker]

 

[StanRAUUS]

Rocker,
Be 3wks before i am back in the office, I'll shoot you a PM...you can have the special instructions. Your' 621 sure looks great, clean with paint!

 

[oarwhat]

Didn't the early 980's have the 336 engine? I know it was a V-8. I once asked my Cat service manager didn't Cat ever make anything bad in your opinion? His reply was the V-8 in the 980's. He thought everything Cat made was great. Quite a statement from him. Keep an eye on it and good luck