Difference between 172 and 197 bare engines?

[AshfordNimbus]

Having a nightmare day. Driving into work this morning I heard a lovely tappety tap from the engine. Pulled over and sounds like top end. Nursed it 1/4 mile to work and confirmed this. I've yet to take anything apart, but have a few questions, hopefully someone knowledgeable with these engines can answer them.

If memory serves me right, doesn't the rocker cover hold the cams?

what differences are there between 172 and 197 bare engines? I've a very good 172 engine at home incase there's further damage to my current engine. Swapping them over isn't a problem, just unsure if mounting points/inlet/exhaust stud patterns match etc?

Cheers all, please try and brighten up my day!

 

[Chrisgti6]

From memory the manifolds won't bolt up as teh mounting points are differnet. Internally they are different also. Cams are different, pistons, the 197 is higher compression.

 

[AshfordNimbus]

Ahh bugger. It's definitely top end. I'm trying a flush and oil change first as I feared the worst earlier, but compressions are good, no swarf in oil, no noticeable misfire and no drop in power when it happened. I'm hoping its just a sticky tappet.

 

[Fernandez]

The 197 has a different head. Also bear in mind that the rocker cover and head are machined together so are a match.

Sorry to hear of the bad luck though, hope you get it sorted soon.

 

[AshfordNimbus]

Thanks, knew it was bit of a long shot! Belts are due now, so no real extra work in taking the cams out and inspecting if a flush doesn't cure it.

 

[Ryan197cup]

Did you find out what it was making the ticky noise then I'm interested as it could be usefull to know ?

 

[Foxspeed]

engine blocks are different...197 has water pump housing built in to engine block...172 doesn't....

 

[AshfordNimbus]

Ryan, I'm unsure yet. It sounds very much like a stuck tappet. Pretty certain it's not bottom end as if I use a screwdriver on the engine, the noise gets louder as I move up the engine. It's either #3 or #4 cylinder. Fingers crossed its nothing more terminal!

 

[AshfordNimbus]

Carried out a flush after work, still no good. Started stripping the top down this evening, hopefully nothing major.

 

[AshfordNimbus]

Stripped down the engine last week. Good news was the belts were done 3k ago. Bad news is I found a rocker arm on its side floating around in the head. No damage done, so fitted a new rocket and tappet. Refitted it all with a new belt and started it up. Tap tap tap, still there! Seems I may of just knocked the rocker arm on removing the rocker cover.

Stripped it down again, all rockers were good. Good compression still. Leak down test was good. Grabbed a bore scope to find part of my old spark plug being mashed into the head by the piston. Off came the head, valves all good, bores perfect, just some marks in the head and piston. All cleaned up and being refitted this week.

Best advice I can give is change your plugs if your unsure of the history. I'm very lucky being a mechanic and having all the special tools, procedures and know-how. I'd dread to think what our garage would charge a customer! This could of easily got wedged in a valve seat causing major damage.