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Collection, Preservation and Display of Old Lawn Mowers

Valve Timing on Suffolk 75G14,Model 25A

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I am reassembling this engine (from a rotovator!)after reconditioning the valve seats and need to get the crankshaft in correct relationship to the camshaft.There is a punch mark on the camshaft cog,but not on the crankshaft cog.There is however a slight indentation on the flange near the crankshaft cog;is this significant?

The engine number is 880294.Does anyone know when it was manufactured?

And can I use unleaded petrol in this engine?

Any help would be most welcome 

Forums

wristpin Sat, 02/11/2013

Bit surprised that you took the cam and crank out to do the valve seats but there you are you've done it!

Easy bit first!  Yes, you can run on unleaded but as the valve seats are cut directly into the cast iron block it may be wise to use a lead substitute, particularly if the engine is going to be heavily loaded. I've got several machines with cast iron valve seats and I occasionally dose the fuel with a bit of Redex or even 2-stroke mixing oil but more often than not don't bother and they don't seem to come to any harm.

It's yonks since I've been that deep into a SIF cast iron lump but cannot recall ever having a problem finding timing marks. Have a really good look for that centre pop mark or possibly a slight chamfer on one tooth. 

Failing that try reassembling with both cam followers on the backs of the their lobes and the piston at TDC and then have a look at what on the crank is opposite the mark on the cam  - if there's something obvious in line you've cracked it but if not look a little to each side. You may (and I'm guessing here) find that either the flywheel or pto side keyway lines up with where you think the mark should be .

Failing all of that you may persuade me to pull a spare engine apart and have a look!

 

arnk Sun, 03/11/2013

In reply to by wristpin

There are timing marks, but they are rather hard to see.  Here are the marks picked out with toothpicks!  This is actually a 98cc crank and camshaft, but the 75cc has similar marks.

Since you have had the gears apart - how do you set the valve tappet gaps?

Al

 

 

PTR48 Mon, 04/11/2013

In reply to by arnk

Thanks wristpin and arnk for your comments and help.

I left the camshaft in place,and removed the crankshaft to see the condition of the bearing surfaces.,which appear to be OK.

The barely visible mark on the flange was indeed one of the lining-up marks,and the crankshaft is now back in place.

I was given this rotovator a short while ago,and know nothing of its previous life,but the exhaust valve seat was badly pitted,and after I'd lapped the valve in,I'd removed enough metal from the valve seat for the tappet clearance to sink to almost nothing.

It should be 15 thou,and as there's no way of adjusting the clearance,I've had to remove the valve and take away some metal from the tip of the valve stem using an oil stone.

PTR48

hillsider Mon, 04/11/2013

In reply to by PTR48

The method you have used to set the valve clearance is the same one that I would use so no worries there.
Back in the good old days of vehicles needing regular decokes garages and workshops would have a machine called a Valvemaster that was made by Black and Decker that would have an attachment that was designed for just this task, sadly I think many of these machines have now been scrapped

greensleaves Tue, 05/11/2013

Hi there  look at the crankshaft side nearest to the camshaft  on the counter weight you will find horizontal   slot cut into the cast metal ,line this up with camshaft dot , does this answer your problem.    timing ( 22-24 deg before topdead centre).rob

hillsider Tue, 05/11/2013

In reply to by wristpin

That's the one, do you have the Vibro Centric valve seat grinding kit to go with it?
If you have look after them carefully, the one that we had at work fell foul of elf and safety so was put up for disposal I was trying to get it officially re homed until the stores mysteriously lost it!

wristpin Tue, 05/11/2013

In reply to by hillsider

Yes, I did but it's a sad story.

I lent it to a friend to do the valve seats on his old British motorbike and he thought that I had given it to him and by the time I got round to asking if he had finished with it he had given it to someone else. In truth I didn't use it much as the set of Nuway cutters is far more civilised but it was complete with about 20 assorted stones and the stone dressing jig.

Put it down to a misunderstanding - still friends!

As you say, every garage had them together with  a Champion spark plug and blaster / pressure spark tester!