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pr2501 28-12-2018 16:44

Resembling of Perkins 4.108
1.New intake valve guide longer than previous.

I have bought rebuilding kit for my Perkins 4.108 from USA. I am now in Panama.
When I have puled out old intake valve guides, I could then compare them to the one from kit. The difference is 3 mm. The dimension in manual is 54,1 mm.
My new are circa 57.

The guide protrusion above of cylinder has to be 20.3 to 20.7 mm.

Can the longer guide protrude for 3 mm in the combustion area?

What could I do?

Lepke 28-12-2018 21:19

Re: Resembling of Perkins 4.108
2 Attachment(s)
While the 4108 is a great engine, British engines of the time had many hand fitted parts. So some things are oversize, planning on being filed/machined. Like the pistons.

The guide isn't extending into the combustion chamber, but into the area above the mushroom end of the valve. I would file/grind to length. Making sure the area where the valve stem rubs is smooth. If you don't, I would be damm sure the valve can close all the way.
While I know how to do head work, I usually take the new valves and guides that come in most kits to a shop specializing diesel heads, so the seats can be ground to fit the new valves. And let them do the assembly of the head.

If you freeze the new guides, they shrink and go into the head easier.

pr2501 30-12-2018 11:54

Re: Resembling of Perkins 4.108
2 Attachment(s)
Is it posible to save valves beds only by grinding by heands? Check my situation on attached images. I was grinding for one hour.

And from where valves are lubrificated inside guides, from mixture of diesel and gas or from oil from top of the engine?

rbk 30-12-2018 12:18

Re: Resembling of Perkins 4.108
Did you get brand new valves? If so you should have the seats cut (by a shop) then a light lapping to seat the valves. Don’t forget to check the clearance from the head to the valve face. If you’re reusing the old valves, make sure each valve is matched to its cylinder (they cannot be interchanged). Lap until there are no more pots in both the seat and the valve. Valve stems are lubricated from above as oil is pumped through the rocker assembly and bathes the springs and valves and flows back down through the galleries eventually to the sump. Also the combustion gases help lubricate to some extent from below.

pr2501 30-12-2018 13:11

Re: Resembling of Perkins 4.108
I have new valves. I have checked and valve beds can be grinded, there is more clarance.

GRIT 30-12-2018 16:27

Re: Resembling of Perkins 4.108
There is such a thing as too much lapping, if that's what you're doing. If you've been at it that long, then I'd probably say, you'd better consider going to a machine shop and getting the seats done. And as was previously posted, it's usually best to have the machine shop take care of the head as a whole. Guides and seats, if not done properly, will cause you a lot of grief.

You're half way there, if you can manage the money, and I hear panama has very affordable tradesmen available, I'd take it to a shop.

Just my two cents.

Edit: I see you have new valves, then get the seats cut, don't just keep lapping. If you've been at it that long, you've now also changed the shape/angle of the valve itself. Bring it to a shop, or it'll just get worse.

Good luck.


pr2501 30-12-2018 17:37

Re: Resembling of Perkins 4.108
Intake are ok. But exsaust are realy got some damage.
I could not image that seats would be so bad. I could see the damage only after some lapping.
I am doing this first time.

And I dit stop once I had got to conclusion that thete is no sense to deform valves to get out good seats.

pr2501 30-12-2018 17:49

Re: Resembling of Perkins 4.108
I have to tell some words here about central America.
Reparing your boat in Cuba, Mexico , Guatemala .... its big difference conparing to Usa- Florida - Jacksonille -Green cove springs marina for exsample. There was a grinding machine shop in entrance of marina ( he does not have machines to grind cylinders ). Here in Cacique at Atlantic coast of Panama I am realy having hard time to get to Good shop in Panama city which is closed alreday from 21 of december.
Also in Usa i had friens and for them was not hard to find some time and help me.
Here I am alone. And if I want some one to get me to Panama city is like asking him to lose half of day + expenses.
I was thinkig that I have forgot my driving license here in Panama, but it is not on the boat.

DougR 01-01-2019 06:52

Re: Resembling of Perkins 4.108
If At all possible you should have the seats cut or ground by an automotive machine shop. There is significant pitting in the seat and from the picture it looks like the seat width is getting too wide and needs to be narrowed.

Also it appears there is a crack in the head between the intake and exhaust seats on #3 cylinder. This might not be serious, but at the minimum the head should be pressure checked.


pr2501 04-01-2019 04:13

Re: Resembling of Perkins 4.108
2 Attachment(s)
I was in the shop. All done. Check Free On Blue Water | Sailing on Tereza

Is the piston direction right one? Check the attached image where "front" label is on the rod also piston mark is (marked with arrow). And the label on second image on top of piston is also on side where front mark on rod is.

I just want to be sure.

pr2501 05-01-2019 14:13

Re: Resembling of Perkins 4.108
I am not sure about next:
Recommended torque tension

- main bearings setscrews : 85 lb/ft
- rod bearings setscrews : 42 lb/ft

Can you confirm?

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