K90 / K91 What Not To Blast?

[71_Bronco 1,072]

I have access to a pretty good sized sand blaster at work, and have been doing parts here and there.

I am rebuilding a K90 / K91 for an RJ-58. I have already sand-blasted the sheet-metal parts for it.

What SHOULDN'T I sand-blast & paint? I don't know if the block will fit in the cabinet.

Obviously, I shouldn't do like the piston & rod etc, but was wondering if there are some parts that shouldn't get blasted & painted. I have seen head's that are painted, but wasn't sure if that would restrict the amount of heat they can disperse.

One part I am concerned with is the aluminum bearing plate. Is this okay to blast & paint? Obviously I would have to mask off the parts for the bearing & oil seal, so that they don't get filled with paint and then not be able to seat them in correctly.

Thanks in advance!

Oh, and yes, I am degreasing & priming them so that no rust can build up on them.

[SousaKerry 502]

I sand blast my heads all the time, Make sure to mask the spark plug hole well. I use an old spark plug as the sand tends to get into the threads and is difficult to remove. Or you can run a tap through the hole afterwards if you have one. I find that as long as I mask off precision machined area's with Duct tape (masking tape won't last) I can sand blast most anything, however cleaning afterward especially engine components must be very thorough.

I actually sand blasted a cast iron carburetor the other day and it came out very nice but I had to spend a couple of hours picking out the grit.

[Don1977 604]

I think a chemical stripper and then use a pressure washer to finish up would be a lot better. I have a engine builder friend that has a stripper tank. He cleaned the paint and rust from a 24" JD wheel for $25. It sure beat a couple of days with a wire brush and sand paper.

[VinsRJ 723]

Nick, I soak my engine blocks in laquer thinner, it removes all the gease and poo. It will also pull all of the paint off. Next I like to glass bead everything; the block, oil pan, bearing plate, head, ect. I find it works better, gets into the pores of the cast iron better and cleans the aluminium without harm. Make sure you do not hit the bore or valve seat areas and soak it down with brake clean and shoot it with a blow gun, ALOT!

[rwilson 128]

I blasted my k91 block with salt. Regular old table salt. After I was dont into the kitchen sink we went for a hot water bath and imediatly taped it off and primed it once dry.

[sorekiwi 761]

I dont blast any internal engine or gearbox stuff at all. I used to blast cylinder heads but have recently decided not to anymore.

I do a fair amount of blasting at work, and I'm put off by the amount of grit that turns up even after several thorough cleanings. I dont believe that every spec of glass bead (or sand etc) can be removed from a gearbox casing or engine block afterwards, so I dont do it on my stuff.

[71_Bronco 1,072]

So for stuff like the sheetmetal that's all done, blasting seems to be king, but for the block and head, it seems there are better ways.

What would be the best way to clean and prep parts for fresh primer and paint?

Should I soak the block and parts in some kind of paint thinner to thouroghly clean and strip the old paint?

Thanks for the help thus far guys, I'm glad I asked.

[TT-(Moderator) 1,145]

This stuff works great for stripping paint and can be found in quite a few stores: http://erisautomotivetools.com/kle-ear322.aspx

A wire wheel on a drill, die grinder, Dremel, etc comes in handy too.

The head could be soaked in your new can of carb cleaner - if you scrape as much carbon off as possible. (it'll dirty up the cleaner real fast)

Any radiator shops in your area? You could get the block "cooked". (soaked in cleaning solution in a "hot tank")

[wheelhorse656 20]

I blast my block but i clean it off with good and then duct tape off all of the the opening cylander and valve seats valve where the bearing plate goes everthing and i make sure it is dry blast it and blow it off really good and then put it in the parts cleaning tank get all the dust off of it then spray it off with paint thinner really good let it dry and then paint it. It takes a while though making sure you get all of the grit out of places they dont belong. I think the next one i might try that stuff TT posted a link to looks like it will work great. Thanks for the link TT.

[71_Bronco 1,072]

TT, great ideas. You never seize to amaze me.

I will be soaking my carb for said motor tomorrow, so I will soak the head to. I got the bulk of the carbon off already, but I will do a better job tomorrow.

[SousaKerry 502]

One more Idea but this one may be tough to find a few years ago we had a company come in to demo a Dry Ice blaster. The idea is that once the dry ice has done it's job it simply evaporates and nothing is left but the dirt and a clean part, no disposal, no media in bad places, and best of all you can blast machinery in place with no diss-assembly. The machine was not too expensive but the dry ice that it used was and not that readily available

http://www.coldjet.com/en/information/what-is-dry-ice-blasting.php

[wheelhorse656 20]

One more Idea but this one may be tough to find a few years ago we had a company come in to demo a Dry Ice blaster. The idea is that once the dry ice has done it's job it simply evaporates and nothing is left but the dirt and a clean part, no disposal, no media in bad places, and best of all you can blast machinery in place with no diss-assembly. The machine was not too expensive but the dry ice that it used was and not that readily available

http://www.coldjet.c...ce-blasting.php

HUH, never heard of this before but sounds really intereasting!! Definally somthing im going to look into!!!

[71_Bronco 1,072]

Let the head & carb soak for 48 hours over the weekend (put in Friday morning, taken out Sunday morning). The carb came out clean as a whistle. The paint that was left on the carb, about 10%, came off with a few strokes of a nylon bristled brush. Now I have to rebuild it with new gaskets and such.

The head though, was a little more problematic. The carbon came off for the most part. Where the carbon was, its almost like it stained the metal. The paint that was on the head would not budge though. Almost like the head of the motor running baked the paint onto the head. The paint looks like over-spray, so there isn't allot of paint on it, but the paint that is there wouldn't come off.

Should I sand-blast the head now? To get that stuff off?

[SousaKerry 502]

I'd blast it

[wheelhorse656 20]

sand blast the whole thing but where the gasket goes on. I do the underide just get off the carbon and stuff that gets built up on the head.

[71_Bronco 1,072]

sand blast the whole thing but where the gasket goes on. I do the underide just get off the carbon and stuff that gets built up on the head.

Was planning on wet-sanding / lapping the head where the gasket sits to get a better seal, so that part I am not too concerned about. I do have a old spark plug to use as a plug while I do the head so I don't hurt the threads.

[shorts 182]

Are you sure that you want to wet sand/lap/polish the gasket surfaces? the factory finish/machine marks give tooth to the surface that helps to grip the gaskets and prevent leaks/blowouts.

Look into different blasting media like slag, walnut shells, corn cobs, or baking soda that are less agressive to the metal alloys

[SousaKerry 502]

I have no problem getting my blasted heads to seal, I will usually stone them once I am done blasting and they seal right up

[71_Bronco 1,072]

Are you sure that you want to wet sand/lap/polish the gasket surfaces? the factory finish/machine marks give tooth to the surface that helps to grip the gaskets and prevent leaks/blowouts.

Look into different blasting media like slag, walnut shells, corn cobs, or baking soda that are less agressive to the metal alloys

This is the link that made me think of wet-sanding / lapping the head:

http://mgonitzke.net16.net/tools/headgasket.pdf

Also, the media I am using is a very very fine sand, not corn cob etc. It is very fine, almost like the stuff in pool filters.